University of Southern California Dissertations and Theses

Applications of advanced electrochemical techniques in the study of microbial fuel cells and corrosion protection by polymer coatings

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Applications of advanced electrochemical techniques in the study of microbial fuel cells and corrosion protection by polymer coatings

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Content APPLICATIONS OF ADVANCED ELECTROCHEMICAL TECHNIQUES IN
THE STUDY OF MICROBIAL FUEL CELLS AND CORROSION
PROTECTION BY POLYMER COATINGS

by

Aswin Karthik Manohar

A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(MATERIALS SCIENCE)

December 2010

Copyright 2010 Aswin Karthik Manohar

ii
Dedication

To my parents

iii
Acknowledgements

I would like to immensely thank my advisor Prof. Florian Mansfeld for his guidance and
encouragement over the years. It has been a great learning experience and I have grown
as a student working under his supervision. I would also like to thank Prof. Edward Goo,
Prof. Michael Kassner and Prof. Steve Nutt for being on my qualifying examination and
dissertation committees and for guiding me in my research work.

I would like to thank Prof. Ken Nealson for being on qualifying examination and
dissertation committees, and for valuable discussions and guidance during our work on
the microbial fuel cell project.

Dr. Peter Zarras at NAVAIR, China Lake is gratefully acknowledged for valuable
technical discussions and for providing the samples for the coatings project. The
microscopy of the scribed samples was performed at Prof. Andrea Armani’s lab. I would
like to thank Prof. Armani and Ashley Maker for their help with the imaging studies.

I would like to thank all the members of the Mansfeld and Nealson groups for their help
and assistance in various forms.

iv
Table of Contents

Dedication ii

Acknowledgements iii

List of Tables vi

List of Figures vii

Abstract xiii

Chapter 1: Applications of Electrochemical Techniques in the Evaluation of
Microbial Fuel Cells (MFCs) 1
1.1 Introduction 1
1.2 Literature Review 3
1.2.1 Background 3
1.2.2 The Use of Electrochemical Techniques in the Study of MFCs 8
1.2.3 The Use of EIS in the Study of the Properties and Performance of
MFCs 11
1.2.4 The Internal Resistance of MFCs 17
1.3 Experimental Approach 19
1.3.1 MFC Design 20
1.3.2 Bacterial Growth Conditions 22
1.3.3 Electrochemical Methods 23
1.4 Experimental Results and Discussion 27
1.4.1 Characterization of the Graphite Felt Anode and the Cathode 27
1.4.2 Cell Voltage – Current and Power - Time Characteristics of the MFC 40
1.4.3 Performance of the MFC over Extended Periods of Operation 47
1.4.4 Characterization of the Stainless Steel Ball Packed Bed Anode 52
1.4.5 Cell Voltage – Current Characteristics of the MFC with SS Ball
Packed Bed Anode 57

v
1.4.6 Analysis of the Internal Resistance of the MFC 59
1.5 Conclusions 74
1.6 Suggestions for Future Work 77
1.7 Chapter 1 References 78

Chapter 2: Effect of Different Chromium Pretreatments and Primers on the
Corrosion Behavior of Polymer Coated Aluminum 2024 86
2.1 Introduction 86
2.2 Literature Review 88
2.2.1 Corrosion Behavior of Aluminum and its Alloys 88
2.2.2. Corrosion Protection of Al Alloys Using Chromate Conversion
Coatings 88
2.2.3 Trivalent Chromium Pretreatment (TCP) 93
2.3 Experimental Approach 94
2.3.1 Sample Preparation 94
2.3.2 Experimental Methods 96
2.4 Results and Discussion 97
2.4.1 Samples with Pretreatment, Primer and Topcoat 97
2.4.2 Analysis of Impedance Spectra of Scribed Samples (With Topcoat) 111
2.4.3 Samples with Pretreatment and Primer, but without Top Coat 118
2.4.4 Analysis of Impedance Spectra of Scribed Samples (Without Topcoat) 127
2.5 Conclusions 130
2.6. Suggestions for Future Work 132
2.7 Chapter 2 References 133

Bibliography 137

vi
List of Tables

Table 1. 1: Fit parameters for the impedance spectra of the anode and cathode
shown in Fig. 1.4 for anolytes A1 and A2. 30

Table 1. 2: Comparison of the fit parameters of the impedance spectra of the anode
at an applied potential and at its OCP with different anolytes. 35

Table 1. 3: Results of analysis of polarization curves with the POLFIT program. 38

Table 1. 4: Comparison of electrode properties before and after the potential sweep
experiment shown. 43

Table 1. 5: Fit parameters for the impedance spectra of the graphite/SS ball anode
for anolytes A1 and A2. 56

Table 1. 6: Fit parameters for EIS data obtained at different applied cell voltages
(anolyte: buffer and lactate). 63

Table 1. 7: Fit parameters for EIS data obtained at different applied cell voltages
(anolyte: buffer, lactate and MR-1). 63

Table 1. 8: Variation of Rm + R
Ω
' with applied cell voltage. 65

Table 2. 1: Formulation of the coatings tested 95

Table 2. 2: E
corr
of scribed samples after 1 day of exposure 113

vii
List of Figures

Fig 1. 1: Schematic diagram of a Proton Exchange Membrane (PEM) Fuel Cell 2

Fig 1.2: Schematic of the construction and principle of operation of a MFC 5

Fig 1.3: Schematic of the glass MFC used in this study (Adapted from (Bretschger
2008) 22

Fig 1.4: Impedance spectra of the anode and cathode with different anolytes in the
graphite felt MFC. 28

Fig 1.5: Equivalent circuit of the impedance response of the anode and cathode in
the graphite felt MFC. 28

Fig 1.6: Comparison of experimental and fitted impedance spectra for the anode (a)
and cathode (b) (data of Fig. 1.4). 31

Fig 1.7: Time dependence of the OCP of the anode before and after adding MR-1 to
the anode compartment. 32

Fig 1.8: Impedance spectra of the graphite felt anode with buffer and lactate as the
anolyte and the cathode at different applied potentials. 33

Fig 1.9: Impedance spectra of the anode with buffer, lactate and MR-1 and the
cathode at different applied potentials 34

Fig 1.10: Cyclic voltammograms for the anode for tests with buffer only and with
buffer and lactate (a) and for test with buffer, lactate and MR-1 (b). 36

Fig 1.11: Polarization curves of the MFC anode with buffer, lactate and MR-1 as
the anolyte (a), and of the cathode (b). 37

viii
Fig 1.12: Polarization curves for the anode in three different anolytes and for the
cathode in buffer solution. 39

Fig 1.13: V-I (a) and P-V (b) curves for the MFC with graphite felt anode with
buffer and lactate as the anolyte. 40

Fig 1.14: V- I (a) and P-V (b) curves of the MFC with graphite felt anode with
buffer, lactate and MR-1 as the anolyte. 42

Fig 1.15: EIS data for the anode and the cathode for tests with buffer, lactate and
MR-1 before and after measurement of V-I curve 44

Fig 1.16: P-t curves for the graphite felt MFC with buffer and lactate as the anolyte
using an applied cell voltage or an external resistor. 45

Fig 1.17: P-t curves for the graphite felt MFC with buffer, lactate and MR-1 as the
anolyte using an applied cell voltage and a constant external resistor. 46

Fig 1.18: Time dependence of the OCP of the anode with different anolytes (arrow
marks indicate tests at an applied potential). 48

Fig 1.19: Time dependence of R
p
of anode with different anolytes (arrow marks
indicate tests at an applied potential). 49

Fig 1.20: V-I (a) and P-V curves (b) for tests with buffer, lactate and MR-1 over a
16 day period 50

Fig 1.21: P-t curves for tests with buffer, lactate and MR-1 at constant cell voltage
V
max
. 51

Fig 1.22: P-t curves for tests with buffer, lactate and MR-1 with resistor connected 52

ix
Fig 1.23: Bode-plots for the SS ball packed bed anode with buffer and lactate as the
anolyte. 53

Fig 1.24: Bode plots of the SS ball packed bed anode with buffer, lactate and MR-1
as the anolyte. 54

Fig 1.25: Equivalent circuit corresponding to the impedance response of the SS ball
packed bed anode with different anolytes. 55

Fig 1.26: V- I (a) and P-V (b) curves of the MFC with a SS ball packed bed anode
with buffer and lactate as the anolyte. 58

Fig 1.27: V- I and P-V curves of the MFC with SS ball packed bed anode with
buffer, lactate and MR-1 as the anolyte. 59

Fig 1.28: Bode plots for the MFC with graphite felt anode at different cell voltages
with buffer and lactate as the anolyte. 60

Fig 1.29: Bode plots for the MFC with graphite felt anode at different cell voltages
with buffer, lactate and MR-1 as the anolyte. 61

Fig 1.30: .E – t (a) and I-t (b) curves at three different cell voltages with buffer,
lactate and MR-1 as the anolyte. 65

Fig 1.31: Bode plots for the MFC with SS ball packed bed anode at different cell
voltages with buffer and lactate as the anolyte. 67

Fig 1.32: Bode plots for of the MFC with SS ball packed bed anode at different cell
voltages with buffer, lactate and MR-1 as the anolyte. 68

Fig 1.33: (a) R
1
and R
2
and (b) C
1
and C
2
for MFC with SS balls at four different
applied cell voltages and two different anolytes. 69

x
Fig 1.34: Dependence of (a) R
int
on cell voltage and (b) P
max
on R
int
for the four
cases studied. 70

Fig 1.35: Impedance spectra of the anode and the cathode at their OCP and for the
MFC with graphite felt anode at V
o
with different anolytes. 72

Fig 1.36: Impedance spectra of the anode and the cathode at their OCP and for the
MFC with SS balls at V
o
with different anolytes. 73

Fig. 2.1: Impedance spectra for sample # 28 at different exposure times. 98

Fig. 2.2: One-time-constant model (OTCM) corresponding to the impedance spectra
shown in Fig. 2.1 99

Fig. 2.3: Impedance spectra for sample # 30 at different exposure times. 100

Fig. 2.4: Impedance spectra for sample # 46 at different exposure times. 101

Fig. 2.5: Equivalent circuit for the coating model 102

Fig. 2.6: Comparison of the impedance spectra of a polymer coated metal with an
intact coating (curve 1) and a deteriorated coating (curve 2) (From
(Mansfeld 2006)) 103

Fig. 2.7: Comparison of the impedance spectra of samples # 28, 30 and 46 after 1
(a), 14 (b) and 31 (c) days of exposure. 104

Fig. 2.8: Time dependence of E
corr
of samples # 28, 30 and 46 during exposure to
0.5N NaCl. 106

Fig. 2.9: Time dependence of C
c
of samples # 28, 30 and 46 during exposure to
0.5N NaCl. 107

xi

Fig. 2.10: Time dependence of R
po
of samples # 28, 30 and 46 during exposure to
0.5N NaCl 108

Fig. 2.11: Time dependence of C
d
of samples # 28, 30 and 46 during exposure to
0.5N NaCl 109

Fig. 2.12: Time dependence of R
p
of samples # 28, 30 and 46 during exposure to
0.5N NaCl. 109

Fig. 2.13: Time dependence of D of samples # 28, 30 and 46 during exposure to
0.5N NaCl. 111

Fig. 2.14: Impedance spectra for scribed sample # 28 at different exposure times. 112

Fig. 2.15 : Impedance spectra for scribed sample # 30 at different exposure times. 113

Fig. 2.16: Impedance spectra for scribed sample # 30 at different exposure times. 114

Fig. 2.17: Optical micrograph of scribed sample # 28 after 3 days of exposure to
0.5N NaCl. 116

Fig. 2.18: Optical micrograph of scribed sample # 30 after 3 days of exposure to
0.5N NaCl. 117

Fig. 2.19: Optical micrograph of scribed sample # 46 after 3 days of exposure to
0.5N NaCl. 117

Fig. 2.20: Impedance spectra of sample # 3 for different exposure times 119

Fig. 2.21: Impedance spectra of sample # 4 for different exposure times 120

xii
Fig. 2.22: Comparison of impedance spectra of samples # 3 and 4 for (a) 1, (b) 14
and (c) 31 days of exposure. 121

Fig. 2.23: Time dependence of E
corr
of samples # 3 and 4 during exposure to 0.5N
NaCl. 122

Fig. 2.24: Time dependence of C
c
of samples # 3 and 4 during exposure to 0.5N
NaCl. 123

Fig. 2.25: Time dependence of R
po
of samples # 3 and 4 during exposure to 0.5N
NaCl. 124

Fig. 2.26: Time dependence of C
dl
(a) and R
p
(b) of samples # 3 and 4 during
exposure to 0.5N NaCl. 125

Fig. 2.27: Time dependence of D of samples # 3 and 4 during exposure to 0.5N
NaCl 126

Fig. 2.28: Time dependence of f
b
of samples # and 3 and 4 127

Fig. 2.29: Impedance spectra of scribed samples # 3 (a) and # 4 (b). 128

Fig. 2. 30: Optical micrograph of scribed sample # 3 after 3 days of exposure 129

Fig. 2. 31: Optical micrograph of scribed sample # 4 after 3 days of exposure 129

xiii
Abstract

The results of a detailed evaluation of the properties of the anode and the cathode of a
mediator-less microbial fuel cell (MFC) and the factors determining the power output of
the MFC using different electrochemical techniques are presented in Chapter 1. In the
MFC under investigation, the biocatalyst - Shewanella oneidensis MR-1 - oxidizes the
fuel and transfers the electrons directly into the anode which consists of graphite felt.
Oxygen is reduced at the cathode which consists of Pt-plated graphite felt. A proton
exchange membrane separates the anode and the cathode compartments. The electrolyte
was a PIPES buffer solution and lactate was used as the fuel. Separate tests were
performed with the buffer solution containing lactate and with the buffer solution with
lactate and MR-1 as anolytes.

Electrochemical Impedance Spectroscopy (EIS) carried out at the open-circuit potential
(OCP) has been used to determine the electrochemical properties of the anode and the
cathode at different anolyte conditions. Cell voltage (V) – current (I) curves were
recorded using a potentiodynamic sweep between the open-circuit cell voltage and the
short- circuit cell voltage. Power (P)-V curves were constructed from the recorded V-I
data and the cell voltage, V
max
, at which the maximum power could be obtained, was
determined. P- time (t) curves were obtained by applying V
max
or using a resistor between
the anode and the cathode that would result in a similar cell voltage. Cyclic

xiv
voltammograms (CV) were recorded for the anode for the different anolytes. Finally,
anodic polarization curves were obtained for the anode with different anolytes and a
cathodic polarization curve was recorded for the cathode.
The internal resistance (R
int
) of the MFC has been determined as a function of the cell
voltage V using EIS for the MFC described above and a MFC in which stainless steel (SS)
balls had been added to the anode compartment. The experimental values of R
int
of the
MFCs studied here are determined by the sum of the polarization resistance of the anode
(R
a
p
) and the cathode (R
c
p
), and therefore R
int
depends on V. The ohmic contribution to
the R
int
was very small. It has been found that R
int
decreased with decreasing cell voltage
as the increasing current flow decreased R
a
p
and R
c
p
. In the presence of MR-1, R
int
was
lower by a factor of about 100 than R
int
of the MFC with buffer and lactate as anolyte.
Additions of SS balls to the anode compartment produced a very large decrease of R
int
.
For the MFC containing SS balls in the anode compartment no significant further
decrease of R
int
could be observed when MR-1 was added to the anolyte.

In Chapter 2, EIS has been used to determine the properties and stability of polymer
coatings based on different chromate or chromate-free pretreatments and primers. Five
sets of coated aluminum 2024 samples were exposed to 0.5N NaCl for a period of 31
days. Impedance spectra of the samples were measured during this period and the
changes of the properties of the different coatings were studied as a function of time.
From the analysis of the fit parameters of the impedance spectra, it was found that the

xv
corrosion protection of the coated samples depended on the type of primer used. The
coating with the chromate based primer provided better corrosion protection than the
coating with the chromate free primer.

After 31 days of exposure, one sample from each set was scribed and exposed to 0.5N
NaCl. The corrosion behavior of the scribed coatings was found to be dependent upon the
type of pretreatment employed. The samples with the chromate conversion coating
pretreatment showed better corrosion resistance in the scribed area than the samples that
were treated by the trivalent chromium based method.

1
Chapter 1: Applications of Electrochemical Techniques in the
Evaluation of Microbial Fuel Cells (MFCs)

1.1 Introduction

Research in alternative energy technologies has been very intense in recent years due to
the dramatically increasing demand for energy, its limited availability and the harmful
effects of fossil fuel use on the environment. Electrochemical power sources including
batteries and fuel cells form a very significant component of the few technologies that
have shown promise as alternate sources of energy. A fuel cell is an electrochemical
device that converts the chemical energy of a fuel and an oxidant into electrical energy.
Methanol and hydrogen are two of the most commonly used fuels as they have extremely
fast electrode kinetics (Hamman et al. 2007). The oxidant that is typically used in fuel
cells is air or oxygen. A schematic diagram of the construction and operation of a Proton
Exchange Membrane (PEM) fuel cell is shown in Fig. 1.1. In a PEM fuel cell, hydrogen,
(the fuel) is oxidized at the anode producing electrons and protons.
− +
+ → e H H 2 2
2
(1)
The electrons produced at the anode pass through the external circuit and reach the
cathode. The protons from the anode pass through the proton exchange membrane to the
cathode and combine with the electrons and oxygen to form water.

O H e H O
2 2
2 4 4 → + +
− +
(2)

2

Fig 1. 1: Schematic diagram of a Proton Exchange Membrane (PEM) Fuel Cell

Fuel cells can be classified into different types based on the design, temperature of
operation and type of fuel used. Proton exchange Membrane fuel cells (PEMFC), direct
methanol fuel cells (DMFC), alkaline fuel cells (AFC), molten carbonate fuel cells
(MCFC) and solid oxide fuel cells (SOFC) are some of the most extensively studied fuel
cells today.

Microbial Fuel Cells (MFCs) are a unique type of fuel cell as they use complex organic
substrates as fuel sources and microorganisms as catalysts for energy production. MFCs
are low power generating devices which are most suitable for application in wastewater
and sewage treatment, microbial community enrichment (Kim et al. 2004), biosensors
(Kim et al. 2003), generation of electricity from aquatic sediments (He et al. 2007).

The application of a MFC generating electric current from wastewater as a biological
Air
Inlet
O
2
H
2
O
Water
H
2
H
+
e
-
e
-
Hydrogen
Hydrogen
Load
Anode Cathode
Proton
Exchange
Membrane
Air
Inlet
O
2
H
2
O
Water
H
2
H
+
e
-
e
-
Hydrogen
Hydrogen
Load
Anode Cathode
Proton
Exchange
Membrane

3
oxygen demand (BOD) sensor has been reported by Kim et al (Kim et al. 2003) who
supplied a MFC with different concentrations of wastewater and observed a direct
relationship between the biological oxygen demand (BOD) of the wastewater and the
current generation from the MFC.

In order to improve the performance of existing MFCs, a better understanding of the
principles of operation and identification of the factors affecting the performance of
MFCs is important. A combination of several advanced electrochemical, analytical and
biological tools is necessary to understand and optimize the performance of MFCs

Traditional electrochemical techniques such as cyclic voltammetry and potentiodynamic
polarization have been used extensively in the study of chemical fuel cell systems. Their
application in MFC studies has not been significantly explored as is evident from a
review of the recent literature on the subject. The aim of this work was therefore to
demonstrate the use of several advanced electrochemical techniques in the study of MFCs
focusing particularly on the application of Electrochemical Impedance Spectroscopy (EIS)
as a key tool in understanding MFC systems.

1.2 Literature Review
1.2.1 Background

A MFC is a device in which bacteria are used to catalyze the oxidation of various organic

4
and inorganic substrates (Logan et al. 2006). A typical MFC consists of an anode and a
cathode compartment which are separated by a proton exchange membrane. The bacteria
which act as the biocatalyst are present in the anode compartment and oxidize the
substrate (fuel) to produce electrons. These electrons pass from the anode through the
external circuit to the cathode where they combine with oxygen present in air and the
protons that reach the cathode compartment through the proton exchange membrane. The
bacteria present in the anode compartment can oxidize complex substrates such as
glucose, lactate, starch and proteins. A schematic of the construction and operation of a
MFC is given in Fig. 1.2.

The electrons produced upon the oxidation of the fuel by the bacteria are transferred to
the anode either by the bacteria themselves or by various external electron transfer
mediators that are added to the anolyte (Logan et al. 2006). The mechanism adopted by
the bacteria in transferring electrons to the anode is a subject of current research. This
transfer can happen through the direct contact of the outer membrane of the bacteria with
the electrode or through soluble mediators secreted by the bacteria that act as electron
shuttles (Bennetto et al. 1983; Bond and Lovley 2003; Chaudhuri and Lovley 2003). This
direct electron transfer can also happen through the formation of conductive bacterial
nanowires (El-Naggar et al. 2008; Gorby et al. 2006). In MFCs, where the bacteria cannot
transfer the electrons to the anode themselves, soluble mediators like thionine, humic acid,
neutral red and anthraquinone-2,6-disulfonate can be added to facilitate the electron
transport from the bacteria to the anode (Sibel et al. 1984; Park et al. 2000). MFCs that

5
use bacteria capable of oxidizing the fuel and transferring the produced electrons to the
anode are generally called ‘mediator-less MFCs’.

Fig 1.2: Schematic of the construction and principle of operation of a MFC

Members of the Shewanella (Bretschger et al. 2007; Bretschger et al. 2010), Geobacter
(Bond and Lovley 2003), Clostridium (Park et al. 2001), Rhodoferax (Chaudhuri and
Lovley 2003), Aeromonas (Pham et al. 2003) and Pesudomonas (Rabaey et al. 2004)
families have been used as bacterial catalysts in MFCs. A detailed analysis of the
metabolic processes and electron transfer characteristics of various Shewanella species in
an MFC has been presented recently (Bretschger 2008; Bretschger et al. 2010).
Fuel
OxidizedFuel
Air
Water
Anode
Cathode
Proton Exchange Membrane
Load
e
-
e
-
Fuel
OxidizedFuel
Air
Water
Anode
Cathode
Proton Exchange Membrane
Load
e
-
e
-
Oxidation
Reduction
Fuel
OxidizedFuel
Air
Water
Anode
Cathode
Proton Exchange Membrane
Load
e
-
e
-
Fuel
OxidizedFuel
Air
Water
Anode
Cathode
Proton Exchange Membrane
Load
e
-
e
-
Oxidation
Reduction

6
In addition to MFCs using only pure cultures of bacteria like Shewanella, MFCs
employing bacterial cultures from domestic waste water (Min and Logan 2004), river and
ocean sediments (Bond et al. 2002; He et al. 2007) and animal wastes (Min et al. 2005;
Yokoyama et al. 2006) have also been developed.
The cathode in an MFC typically consists of a catalyst such as platinum to increase the
rate of the oxygen reduction reaction. Platinum is very expensive and is sometimes
poisoned by the cross over of micro-organisms or organic compounds from the anode
compartment. The possible decrease in the performance of a platinum catalyst at neutral
pH has been mentioned in the literature (Zhao et al. 2006). Several authors have
discussed the replacement of a platinum catalyst at the cathode by less expensive and
stable catalysts. MFCs using ferricyanide as an electron mediator in the cathode reaction
have been reported to show comparable performance characteristics as MFCs using
platinum catalysts (Aelterman et al. 2006). Park and Zeikus used a cathode modified with
compounds containing Fe
3+
which was reduced to Fe
2+
during the cathodic reaction. The
Fe
3+
ions were then regenerated by using the oxygen supplied (Park and Zeikus 2002;
Park and Zeikus 2003). The iron compounds in this case acted as an electron mediator
between the cathode and the reductant (oxygen). You et al (You et al. 2006) have used
permanganate as the electron acceptor and have compared the performance of their MFC
with cells employing oxygen and ferricyanide (You et al. 2006). In addition to using
bacteria as the catalyst to oxidize the fuel in the anode compartment, MFCs with bacteria
as a catalyst for the cathodic reaction have also been developed (He and Angenent 2006;
Clauwaert et al. 2007b). A MFC using a bipolar membrane, where the cathodic reaction

7
is the reduction of ferric ions to ferrous ions, has been demonstrated by Ter Heijne et al
(Ter Heijne et al. 2006). The ferric ions are reduced to form ferrous ions at the cathode
and the regeneration of the ferric ion has been accomplished by using, Acidithiobacillus
ferrooxidans (Ter Heijne et al. 2006). Manganese dioxide was used as an electron
transfer mediator in a biocathode based MFC by Rhoads et al (Rhoads et al. 2005). In this
study, Mn
4+
ions from manganese dioxide were reduced to Mn
2+
ions at the cathode. The
Mn
2+
ions were then oxidized by manganese oxidizing bacteria such as Leptothrix
discophra resulting in the regeneration of Mn
4+
ions. The authors observed that the
manganese reduction cathode increased the current output considerably (Rhoads et al.
2005).

In addition to the production of electric current and treatment of organic waste matter in
waste water treatment plants, other major areas where MFCs have shown promise are the
production of bio-hydrogen, denitrification and in the bioremediation of various heavy
metals. Clostridium butyricium immobilized in polyacrlamide gel has been used in the
production of hydrogen gas from glucose. The effect of temperature, pH and long term
storage on the rate of hydrogen production was evaluated by Karube et al (Karube et al.
1976). Cai et al have published a study where biohydrogen production was achieved by
using sewage sludge without the addition of any hydrogen generating seed bacteria
present in the medium (Cai et al. 2004). Liu et al demonstrated the generation of
hydrogen gas in the cathode compartment of a mediator-less microbial fuel cell (Liu et al.
2005). The authors used completely anaerobic anode and cathode compartments and

8
acetate was used as the fuel in the anode compartment. When a cell voltage greater than
250mV was applied on the MFC, the protons and electrons that were produced upon the
oxidation of acetate by the bacteria in the anode compartment reached the cathode and
formed hydrogen gas. (Liu et al. 2005). Clauwert et al have demonstrated that biological
denitrification can be achieved in a MFC by using a bacterial cathode (Clauwaert et al.
2007a). Gregory and Lovley have showed that bioremediation of uranium (VI) present in
ground water to uranium (IV) could be accomplished using Geobacter Sulfurreducens
which can use electrodes polarized at -500mV (vs Ag/AgCl reference electrode) as
electron donors to reduce U(VI) to U(IV) (Gregory and Lovley 2005). The removal of the
U(IV) formed is very convenient as it was found to stick to the surface of the electrode
and was stable in the absence of oxygen. The remediation and removal of U(VI) from
contaminated waters and sediments carried out using Geobacter Sulfurreducens was
considered to be very economical and complete compared to other remediation
techniques (Gregory and Lovley 2005).

1.2.2 The Use of Electrochemical Techniques in the Study of MFCs

Despite the extensive literature available on the general principles and on various
improved designs of MFCs, few publications have discussed the applicability and the
effectiveness of advanced electrochemical techniques in studying MFC systems. In a
review paper (Logan et al. 2006), the different types of electrochemical instrumentation
for the measurement of cell voltages and electrode potential as well as the use of cyclic

9
voltammetry (CV) and polarization curves have been discussed. Some of these
techniques require the placement of a reference electrode in one or both compartments of
the MFC.

In most studies of MFCs cell voltage – current (V-I) curves are obtained by measuring
the stable voltage generated across various external resistors connected between the
anode and the cathode. From these V-I curves, power – current (P-I) and power-cell
voltage (P-V) curves and the maximum power P
max
can be calculated. This step resistor
method is highly time consuming and one cannot easily obtain the complete V-I
characteristic from the open-circuit cell voltage V
o
to the short-circuit cell voltage V
sc
of
the MFC. The number of data points that are typically measured using this method is
quite low. Another method to obtain the V-I curve of a MFC uses a potentiostat to scan
the voltage from V
o
to V
sc
and measure the current as a function of cell voltage. The scan
rates used for these measurements should be very low so that the system can be treated to
be in a quasi-steady state at each applied cell voltage. This method not only offers good
control over the experiment, but also results in a reduction of the time of the
measurement while a large number of data points can be obtained.

Potentiodynamic polarization curves of the anode and cathode allow to determine the
polarization behavior of these electrodes. Using this type of measurement, the electrode
that limits the overall performance of the MFC can be identified (Mansfeld 2007a). It has
been suggested that galvanodynamic polarization measurements could be used to

10
determine electrode performance (Zhao et al. 2006; Zhao et al. 2009). Zhao et al also
used galvanodynamic polarization curves to explore the kinetics of oxygen reduction at
the cathode (Zhao et al. 2005). Performing potentiodynamic polarization measurements
in a large potential range for the anode and cathode, while providing a wealth of
information, might lead to irreversible changes of the electrode surface. Oldham and
Mansfeld have discussed the concept of the polarization resistance technique, where the
current-potential behavior of an electrode can be measured within the vicinity of its open-
circuit potential (OCP) (Oldham and Mansfeld 1973; Mansfeld 2005). A perspective on
the historical development of this technique and its application in the analysis of
corrosion systems has been provided recently (Mansfeld 2009). Using this method one
can determine the Tafel slopes and the exchange current density, i
o
of an electrode
reaction from data obtained in the pre-Tafel region without significantly changing the
properties of the electrode (Mansfeld 2005).

Cyclic Voltammetry (CV) has been used quite extensively in the study of MFCs. Prasad
et al used CV to demonstrate the electrochemical activity of H anomola in phosphate
buffer with successive additions of lactate (Prasad et al. 2007). Rabaey et al used CV to
demonstrate the effect of metabolites excreted by the bacteria on their electrochemical
activity (Rabaey et al. 2004). In their study, while some bacteria showed no
electrochemical activity in the absence of metabolites, some bacteria showed no decrease
in their electrochemical activity when their metabolites were removed. The authors
attributed these results to be due to the difference of the electron transfer mechanism

11
adopted by various bacteria. Fricke et al have employed CV to study the electron transfer
processes taking place in an MFC (Fricke et al. 2008). They have studied a MFC utilizing
Geobacter Sulfurreducens as the biocatalyst and have performed CV on the anode at
different stages during biofilm formation. They concluded that the data from CV alone
cannot be used to conclusively elucidate the mechanism of electron transfer adopted by
the bacteria (Fricke et al. 2008). CV has also been used to demonstrate the catalytic
activity of cobalt tetramethoxyphenylporphyrin (CoTMPP) catalyst modified graphite
electrodes as cathodes in MFCs. It was reported that the oxygen reduction current
increased in the presence of the catalyst (Zhao et al. 2005). CV has been used to study the
catalytic activity of polyanilene modified platinum anodes in a MFC at different growth
and fermentation phases of E. coli K12 bacteria present in the anode compartment
(Niessen et al. 2004). The authors found that the catalytic activity of the bacteria was
very high during fermentative conditions. Similar measurements at different growth
phases of the bacterial consortia in an MFC were carried out by Rabaey et al (Rabaey et
al. 2004).

1.2.3 The Use of EIS in the Study of the Properties and Performance of MFCs

EIS is one of the most powerful and extensively used techniques for the study of
electrochemical systems. Its use in the study of localized corrosion, corrosion protection
using polymer coatings, corrosion inhibition, batteries and fuel cells has been well
documented (Mansfeld and Kendig 1985; Mansfeld 1990; Mansfeld 1995; Hjelm and

12
Lindbergh 2002; Taberna et al. 2003; Gomadam and Weidner 2005; Mansfeld 2006b).
The advantage that EIS possesses over most other electrochemical techniques is that
using EIS one can make accurate measurements on the system at an operating potential
(E) without significantly perturbing the steady-state existing at the electrode/electrolyte
interface. This feature makes it particularly useful in corrosion research, where
measurement of system parameters such as the corrosion rate at the equilibrium state of
the system is necessary. Mansfeld and Kendig (Mansfeld and Kendig 1985) were the first
to use the term “Electrochemical Impedance Spectroscopy” in a paper entitled
“Electrochemical Impedance Spectroscopy of Protective Coatings”, published in
Materials and Corrosion in 1985 (Mansfeld 2006b).

In EIS, the properties of an electrode/electrolyte interface are determined as a function of
the frequency of a small amplitude ac signal at a fixed operating point (E, I) of the system.
Since only a small amplitude ac signal that is applied, for example 10mV, EIS is in
principle a non-destructive electrochemical technique. The impedance of a system can be
represented by Z = Z’+jZ” where Z’ and Z” are the real and imaginary parts of the
complex number Z respectively. The impedance, ‘Z’ is associated with a phase angle φ
which is calculated as:
φ = tan
-1
(-Z”/Z’) (3)
The experimentally measured impedance values, Z(jω) = Z’+jZ’’ are usually plotted in
one of the two different ways:
1. Complex-plane plots.

13
2. Bode plots.
In the complex plane plot, the real part of the impedance, Z’ is plotted against the
imaginary part, Z”. Usually, the negative values of Z” are plotted on the positive Y-axis.
In the Bode plot, the logarithm of the impedance modulus |Z| and the phase angle φ are
plotted against the logarithm of the frequency f of the applied ac signal.

In order to obtain electrochemical parameters from the measured impedance spectra, they
are fitted to appropriate equivalent circuits (ECs). These ECs contain electrical
components such as resistors, capacitors and inductors in series and parallel combinations.
Each of these components correlate to a particular electrochemical process or property of
the system. Data fitting and determination of the fit parameters from impedance spectra
are usually performed with software developed for impedance data analysis. All
impedance data presented in this study have been fitted using the ANALEIS software
developed by Shih and Mansfeld (Mansfeld et al. 1992; Mansfeld et al. 1993; Mansfeld
2006b).

In the study of MFCs, EIS can be used to determine the electrochemical properties of the
anode and cathode at their open-circuit potentials (OCPs) or at an applied potential. It can
also be used to measure the internal resistance of the MFC as a function of cell voltage. A
review of the application of EIS in the study of MFCs has been provided by He and
Mansfeld (He and Mansfeld 2009; Manohar et al. 2009).

14
In a study conducted with Geobacter sulfurreducens, the impedance response of a bare
graphite paper anode has been compared with the impedance response after the
entrapment of bacteria on these electrodes (Srikanth et al. 2008). The study revealed a
significant reduction of the polarization resistance and an increase of the capacitance of
the anode in the presence of bacteria. The authors concluded that these observations
indicate an increase in the rate of the redox process at the anode due to the presence of a
conductive biofilm on the anode surface (Srikanth et al. 2008)

A comparison of the impedance response of different electrodes has been reported by
Ouitrakul et al (Ouitrakul et al. 2007). In this study, the authors have tested various
electrode materials like silver, aluminum, nickel, stainless steel and carbon cloth. It was
observed that most of these metal electrodes had high impedance and that carbon cloth
electrodes and silver electodes exhibited low polarization resistance.

Ramasamy et al. 2008 have employed EIS to study the progress of biofilm formation on
an electrode surface. The impedance spectra of the anode were measured at different time
periods in a MFC. The polarization resistance of the anode decreased considerably within
three weeks, suggesting improved kinetics of the oxidation reaction occurring on the
anode. The authors have also observed that even with a very mature biofilm, the
polarization resistance of the anode was significantly higher than the polarization
resistance of the cathode (Ramasamy et al. 2008).

15
EIS has been used by Qiao et al in studying carbon nanotube/ polyaniline composite
coated on nickel foam electrodes. They have observed that the polarization resistance
decreased with increased loading of the carbon nanotubes on the electrode. An
improvement in the cell performance has also been reported (Qiao et al. 2007).

Borole et al (Borole et al. 2010) have reported the effect of biofilm enrichment at the
anode in a MFC over a period of two months. In their study it was observed that the
impedance of the anode and cathode decreased considerably during the first 43 days of
operation. They also found an increase of the capacitance of the anode during the
operation of the MFC (Borole et al. 2010).

EIS has been used in identifying and studying the electrochemical behavior of
endogenously secreted mediators in MFCs (Ramasamy et al. 2009). In this study, the
authors added riboflavin in a large concentration to an MFC and observed a change in the
impedance spectra in the low-frequency region. When comparing this impedance
spectrum with the one measured without any external mediator, a significant increase of
the rate of electron transfer from the substrate to the electrode in the presence of
riboflavin was observed. The soluble mediators that are secreted by Shewanella were
found to yield distinct time constants in the impedance spectra. In all these cases, the
redox reactions involving the mediators were 10-15 times faster than the oxidation of the
substrate (Ramasamy et al. 2009).

16
Aaron et al have used EIS to investigate the effect of ionic strength and fluid flow rate on
the performance of an air-cathode MFC (Aaron et al. 2010). The analysis of the
impedance spectra showed that upon increasing the circulation rate of the fluid and the
ionic strength of the electrolyte, the impedance of the cathode was reduced which
resulted in an increased power output from the MFC. It was also observed that the
impedance of the anode was not affected by changes in ionic strength indicating that no
charged species present in the electrolyte were involved in the anodic reaction. A change
in the properties of the cathode upon changing the anode fluid flow rate has also been
reported. The authors stated that this result could be due to a very stable biofilm on the
anode and an increase in the rate of proton transport to the cathode from the anode
(Aaron et al. 2010).

EIS has been used to investigate the effect of different experimental conditions on an
MFC with a rotating cathode configuration. The polarization resistance of the anode was
higher with a rotating cathode compared with cathode which was stationary. The rotation
of the cathode increased the concentration of dissolved oxygen which decreased the rate
of the anodic reaction (He et al. 2007). The cathode rotation resulted in better ion
transport which caused a slight decrease in the ohmic resistance of the MFC (He et al.
2007).

He et al have employed EIS to study the effect of electrolyte pH in an air-cathode MFC
(He et al. 2008). The authors found that the polarization resistance of the anode was the

17
lowest when the pH of the electrolyte was 7, and the polarization resistance of the
cathode decreased continuously as the electrolyte pH was increased from 5 to 10. The
authors concluded that the at neutral pH values the anode performed optimally and that
the rate of the oxygen reduction reaction on the cathode increased with an increase in the
pH of the electrolyte (He et al. 2008, He and Mansfeld 2009).

1.2.4 The Internal Resistance of MFCs

The performance of a MFC system is dependent upon several factors which can be
broadly classified as kinetic and transport limitations. Kinetic limitations arise from the
polarization resistance of the anode and the cathode and transport limitations arise from
diffusion related processes in the MFC (He et al. 2006). The performance of MFCs may
be limited by the rate at which the fuel is oxidized by the bacteria, the efficiency of
electron transport from the bacteria to the anode, the rate at which oxygen reduction takes
place at the cathode, the ohmic resistance of the proton exchange membrane, the solution
resistance between the anode an the cathode and the temperature of operation of the MFC.
The rate at which the fuel is oxidized at the anode and the rate of oxygen reduction at the
cathode are related to the polarization resistance of the anode and cathode, respectively.
The polarization resistance of the anode and cathode, together with the resistance of the
membrane and the other ohmic contributions constitute a parameter known as the internal
resistance, R
int
. In addition to the resistance of the membrane, the other ohmic
contributions to R
int
arise from the resistance of the anolyte, catholyte and the resistance

18
of the electrodes and the electrode leads.

R
int
is directly related to the maximum power that can be generated by the MFC. Very
little information can be found concerning experimental data for R
int
of MFCs. There
seem to be two different interpretations for R
int
in the existing literature for MFCs. Logan
et al (Logan et al. 2006) state that R
int
contains contributions from the polarization
behavior of the anode and cathode in addition to contributions from ohmic components.
Aelterman et al (Aelterman et al. 2006) seem to define R
int
as a parameter that contains
only the ohmic components as indicated by the statement that R
int
values were determined
using the current interrupt method which can be used to measure the ohmic component of
R
int
, but not the contributions from the polarization behavior of the anode and the cathode.

The current interrupt method is a frequently used method in the analysis of proton
exchange membrane (PEM) fuel cells, where the ohmic resistance is one of the key
factors determining the performance of the system (Cooper and Smith 2006). The
technique is based on the principle that when the electrical circuit of a fuel cell that is
operating at steady state is opened, there will be an instantaneous drop in the voltage
before it reaches the open-circuit cell voltage. This instantaneous drop occurs as a result
of the sudden disappearance of the ohmic resistances in the fuel cell. The resistance value
determined using this technique yields only the ohmic component of R
int
. However,
MFCs are bio-electrochemical systems in which microbial activities play an important
role and are associated with activation and concentration resistances (He and Mansfeld

19
2009). Under such conditions, the charge transfer resistance of the electrodes becomes
significant and R
int
cannot be determined from the current interrupt method.

EIS provides a more precise evaluation of R
int
than the current interrupt technique or
calculation from the slope of the cell voltage - current curve of the MFC (He et al. 2006;
Fan et al. 2007; Mansfeld 2007b; You et al. 2007; You et al. 2008). EIS also provides a
complete evaluation of the various components of R
int
and allows to determine the
variations of R
int
with increasing current flow through the cell. This can be accomplished
by measuring the impedance spectra of the cell at various applied cell voltages.
1.3 Experimental Approach

In the present study the electrochemical properties of the anode and the cathode in a
mediator-less MFC have been characterized using several advanced electrochemical
techniques. Measurements were performed in PIPES buffer solutions with and without
Shewanella oneidensis MR-1. Cell voltage–current (V-I) curves and the power produced
by the MFC were monitored for extended time periods. The electrochemical techniques
used in this study included EIS, potential sweeps, current-time (I-t) curves at a fixed cell
voltage or with a resistor connected between the anode and the cathode, CVs and
potentiodynamic polarization curves. These measurements were made possible by
placing Ag/AgCl reference electrodes in both the anode and the cathode compartments of
a laboratory model MFC. The results of these tests discussed in the following sections
indicate that utilizing a combination of different electrochemical techniques to evaluate

20
MFC performance yields a much more complete understanding of how MFCs work.

Two different configurations of the anode have been used in this study. In the first
configuration, a graphite felt electrode served as the anode and in the second
configuration, stainless steel (SS) balls served as a packed bed electrode with a graphite
felt serving as the feeder electrode. A packed bed electrode is one of the most extensively
used designs in electrochemical engineering as it increases the effective surface area of
the electrode while maintaining good mass transport (Heitz and Kreysa 1986). SS balls
were chosen as they do not corrode upon polarization.

A comprehensive analysis of R
int
of the MFC with different anolytes and two different
anode configurations and the dependence of R
int
on cell voltage has also been performed.

1.3.1 MFC Design

Experiments were conducted with a dual compartment glass MFC assembled with a
proton-exchange membrane (Nafion® 424, DuPont) separating the anode and cathode
compartments (Fig. 1.3) (Design adapted from (Bretschger 2008)). Two different anode
configurations, one with a conventional graphite felt anode and another with a stainless
steel packed bed structure and a graphite felt feeder electrode were investigated.

21
MFC with porous graphite felt as the anode: Bare graphite felt (Electrolytica) was used
as the anode and the cathode. The cathode was electroplated with platinum at a loading
of 0.15 mg/cm
2
. Each electrode had an apparent surface area of 20 cm
2
and was
connected to Pt-wire leads by a conductive carbon epoxy (EPOX-4, Electrolytica). The
anode and cathode compartments had a working liquid volume of 25 mL.

MFC with packed bed of stainless steel balls as the anode: In this type of cell
construction, stainless steel (SS) balls of 2mm diameter each were used as a packed bed
anode filling the entire anode compartment. The total surface area of the SS balls was
about 130cm
2
. The graphite felt electrode with a platinum lead acted as the feeder
electrode. The cathode was platinum plated graphite felt identical to the electrode used in
the other configuration. The same glass cell arrangement as that shown in Fig. 1.3 was
used.

22

Fig 1.3: Schematic of the glass MFC used in this study (Adapted from (Bretschger 2008)

The assembled MFC was autoclaved at 121
o
C for fifteen minutes prior to the addition of
any liquid media. Sterile Ag/AgCl reference electrodes (Bioanalytical Systems) were
inserted into both the anode and cathode compartments. Anaerobic conditions were
maintained in the MFC anode by continuously passing filtered nitrogen gas through the
compartment at a rate of 20 mL/min. Aerobic conditions were maintained in the cathode
compartment by continuously passing air at a rate of 40 mL/min (Fig. 1.3).
1.3.2 Bacterial Growth Conditions

Shewanella oneidensis MR-1 was grown in a PIPES-buffered minimal media (pH 7.0)
containing 18 mM lactate as the sole electron donor, 50 mM PIPES, 7.5 mM NaOH, 28
Clamp holding ion
exchange membrane
Graphite felt
anode
Pt coated graphite
felt cathode

Fuel

V
Nitrogen
gas
Air
40 mL/min

23
mM NH
4
Cl, 1.3 mM KCl, 4.3 mM NaH
2
PO
4
·H
2
O and 10 mL/L each of vitamin, amino
acid and trace mineral stock solutions. Batch cultures were grown at 30°C and agitated at
a rate of 140 rpm until the late stationary phase was achieved. The cells were then
harvested and injected into the MFC such that an optical density (OD
600
) of 0.4 was
achieved in the anode compartment. The buffer served as the diluting medium.

The buffer solution contained 50 mM PIPES (C
8
H
18
N
2
O
6
S
2
) and 7.5 mM NaOH (pH 7.0).
The same buffer solution was used in the anode and the cathode compartments. Lactate
served as the sole electron donor for the bacteria in the anode compartment.

Experiments were performed with graphite felt as the anode and with a SS ball packed
bed anode with two different anolytes:

(A1) With buffer and lactate as the anolyte.
(A2) With buffer, lactate and MR-1 as the anolyte.

1.3.3 Electrochemical Methods

Electrochemical Impedance Spectroscopy (EIS): EIS measurements were performed for
the anode, the cathode and the MFC in a frequency range of 100 kHz to 1 mHz. In some
cases a lower limit of 5mHz was used. For the tests with the graphite felt electrodes, an
ac signal of 10mV was used as the input signal, whereas for the tests with packed bed

24
electrodes, an ac signal of 20mV was applied. Impedance spectra of the anode were
recorded using the anode as the working electrode and the cathode as the counter
electrode while impedance spectra of the cathode were recorded using the cathode as the
working and the anode as the counter electrode. During these measurements, a Ag/AgCl
electrode placed in the compartment of the working electrode was used as the reference
electrode. Impedance measurement of the anode and cathode were conducted either at
their corresponding open-circuit potentials (OCP) or at an applied potential (E
app
).

EIS measurements were also performed for the MFC at several applied cell voltages. For
these measurements, the anode was used as the working electrode and the cathode was
used as the reference as well as the counter electrode. Measurements were taken at four
different applied cell voltages, i.e. the open-circuit cell voltage (V
o
), the cell voltage at
which the maximum power is obtained, (V
max
), the cell voltage at which half the
maximum power is obtained, (V
1
) and the short-circuit cell voltage (V
sc
). All impedance
spectra presented in this study were analyzed using the ANALEIS software developed by
Mansfeld and co-workers (Mansfeld et al. 1992; Mansfeld et al. 1993; Mansfeld 2006b).

Potential Sweep: Potential sweep experiments were carried out at a scan rate of 0.1 mV/s
from V
o
, where the current I = 0, to V
sc
= 0, where I = I
max
. The working electrode lead
of the potentiostat was connected to the anode and the counter and reference electrode
leads were connected to the cathode of the MFC. Power (P)-V curves were calculated
using the data obtained from the V-I curves. From these P-V curves, the cell voltage

25
(V
max
) at which the maximum power was obtained was determined. The cell voltage at
which half the maximum power was obtained (V
1
) was determined in such a way that
V
max
>V
1
>V
sc
.
Current - time curves: Two different methods were used to measure I-t curves of the
MFC: 1) a potentiostat was used to maintain the cell voltage at V
max
and the current, (I)
was measured as a function of time (t); and 2) an external resistor (R
ext
) was applied
between the anode and cathode and I was measured as the voltage drop across the
resistor.

The value of V
max
that needs to be applied was determined from the power- cell voltage
curve. R
ext
was calculated based on the V-I and P-I curves to produce a cell voltage close
to V
max
. The first method allows more precise control of the experiment, while the
second method is closer to practical applications. Measurements of I-t curves were
carried out for 12 hour periods. P-t curves were constructed using the I-t data. Power as
a function of time, P(t), was calculated as P(t) = I(t)·V
max
for method 1 (applying V
max
),
and P(t) = V(t)
2
/R
ext
for method 2 (using an external resistor).

Cyclic Voltammetry (CV): CV was carried out for the anode for each anolyte using a
potential range of –700 mV to +750 mV (vs. Ag/AgCl) at a scan rate of 25 mV/s. For
these measurements, a Ag/AgCl electrode placed in the anode compartment was used as
the reference electrode.

26
Polarization curves: Potentiodynamic polarization curves were recorded for each test
condition at a scan rate of 0.167 mV/s. Anodic polarization curves were recorded for the
anode between E = OCP
a
– 30 mV and E = + 1V (vs. Ag/AgCl). Cathodic polarization
curves of the anode were recorded between E = OCP
a
+ 30 mV and E = -1V (vs.
Ag/AgCl). Cathodic polarization curves of the cathode were measured between E = OCP
c
+ 30 mV and E = -1V (vs. Ag/AgCl) where OCP
a
and OCP
c
are the OCP for the anode
and the cathode, respectively. Polarization experiments were also performed for the
anode and the cathode in the potential region -30mV < OCP < +30mV.

Prior to each type of electrochemical measurement, the MFC was allowed to remain at
the open-circuit voltage (OCV) for several hours, such that a stable OCP of the anode and
the cathode could be observed before measurements were taken.

A Gamry PCI4/300 potentiostat was used for the electrochemical measurements. Gamry
EIS300 software was used for recording of impedance spectra, DC105 software was used
for recording of polarization curves and PHE200 software was used for carrying out the
CV experiments. The analysis of impedance data was perfomed with appropriate modules
of the ANALEIS software (Mansfeld et al. 1992; Mansfeld et al. 1993; Mansfeld 2006b).
Data from polarization curves in the vicinity of the OCP of the anode and cathode were
analyzed using the POLFIT program (Shih and Mansfeld 1992).

27
1.4 Experimental Results and Discussion

Electrochemical measurements were performed in buffer and lactate (A1) and with buffer,
lactate and MR-1 (A2) as anolyte using MFCs with a graphite felt anode and with SS
balls as a packed bed type anode.

1.4.1 Characterization of the Graphite Felt Anode and the Cathode

EIS Data
The impedance spectra for the graphite felt anode and the platinum plated graphite felt
cathode at their corresponding OCPs are shown in Fig. 1.4 for both anolytes. The EIS
data are displayed as Bode plots, where the logarithm of the impedance modulus |Z| and
the phase angle are plotted vs. the logarithm of the frequency, f of the applied ac signal.

The impedance spectra of both the anode and the cathode follow a one-time constant
model (OTCM), in which the solution resistance (R
s
) is in series with a parallel
combination of the capacitance of the electrode (C) and its polarization resistance (R
p
) as
shown in Fig. 1.5. The impedance modulus, |Z| for the OTC model is given by:
|Z| = R
s
+ R
p
/(1 + (jωCRp)
α
) (4)
where ω = 2πf and 0 ≤ α ≤ 1 . Τhe parameter α is used to account for the non-ideality in
the capacitive behavior of the electrodes (Mansfeld 2006b).

28
-3 -2 -1 0 1 2 3 4 5
0
1
2
3
4
5
6
Anode (A1), OCP= 0.197V
Cathode (A1), OCP=0.360V
Anode. (A2). OCP= -0.481V
Cathode (A2). OCP= 0.305V
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0

Fig 1.4: Impedance spectra of the anode and cathode with different anolytes in the
graphite felt MFC.

Fig 1.5: Equivalent circuit of the impedance response of the anode and cathode in the
graphite felt MFC.

29
The impedance spectrum of the anode in A1 was capacitive in the entire frequency region
except in the high-frequency region, which is dominated by R
s
. The frequency
dependence of the impedance and the phase angle φ at low frequencies demonstrates that
polarization resistance of the anode R
a
p
had decreased considerably after MR-1 was
added to the anolyte (anolyte A2). A dc limit can be observed in the low-frequency
region of the impedance spectra where φ reached values close to 0
o
. This decrease was
accompanied by a sharp decrease of the OCP of the anode (OCP
a
) from 0.197V to -
0.481V in the presence of MR-1 in the anolyte. According to mixed potential theory, this
decrease of R
a
p
and OCP
a
in the presence of MR-1 suggests that the rate of the redox
reaction that takes place at the anode is considerably increased (Mansfeld 2006a).

The polarization resistance of an electrode R
p
, is inversely proportional to the exchange
current density of the reaction i
o
. The frequency dependence of φ in the low-frequency
region of the spectra indicates that the polarization resistance of the cathode R
c
p
is much
lower than R
a
p
, i.e. the i
o
for oxygen reduction reaction at the cathode is much larger than
i
o
for the lactate oxidation reaction taking place at the anode. The much higher
capacitance value for the cathode (C
c
) is due to the higher active surface area of the Pt-
plated graphite cathode (Fig. 1.4). The cathode/anode active surface area ratio was about
24:1 based on the ratio of the capacitance values.

The EIS data shown in Fig. 1.4 were analyzed using the one-time constant model shown
in Fig. 1.5. The fit-parameters for the impedance spectra of the anode and the cathode

30
shown in Fig. 1.4 are summarized in Table 1.1 for both anolytes. The most significant
result of this analysis is the large decrease of R
a
p
in the presence of MR-1 (Table 1.1). C
a

did not change when MR-1 was present in the anolyte. The fact that C
c
remained more or
less constant during the various tests discussed here suggests that contamination of the
cathode due to possible cross-over of the anolyte did not occur.

Table 1. 1: Fit parameters for the impedance spectra of the anode and cathode shown in
Fig. 1.4 for anolytes A1 and A2.

Anode Cathode
Fit Parameter A1 A2 A1 A2
R
p
(Ohm) 7.79X10
6
1.02X10
4
8.32X10
3
8.51X10
3

C (F) 9.22X10
-4
9.70X10
-4
6.22X10
-2
6.62X10
-2

R
s
(Ohm) 1.5 1.1 5.5 5.3

The slightly lower solution resistance in the anode compartment (R
s
a
) is probably due to
the presence of sodium lactate in the anolyte which increases its ionic conductivity.

Fig. 1.6 shows a comparison of the experimental and the fitted impedance spectra for the
impedance data presented in Fig. 1.4. Very good agreement between the two data sets
was obtained for the EIS data obtained with and without MR-1 which shows that the
equivalent circuit shown in Fig. 1.5 can be used to represent the impedance response of
the anode and cathode of the MFC.

31
1.00E+00
1.00E+03
1.00E-04 1.00E-02 1.00E+00 1.00E+02 1.00E+04 1.00E+06
Log f (Hz)
Log Z (Z in Ohms)
-90
-60
-30
0
Phase angle (degrees)
Fit data Experimental data
a)
0
3
5
-4 -2 0 2 4 6

1.00E+00
1.00E+02
1.00E+04
1.00E-04 1.00E-02 1.00E+00 1.00E+02 1.00E+04 1.00E+06
Log f (Hz)
Log Z (Z in Ohms)
-90
-60
-30
0 Phase angle (degrees)
Fit data Experimental data
-4 -2 0 2 4 6
b)
0
2
4

Fig 1.6: Comparison of experimental and fitted impedance spectra for the anode (a) and
cathode (b) (data of Fig. 1.4).

Potential-time data:
In order to obtain a more detailed understanding of the change in the OCP of the anode
upon addition of MR-1 to the anode compartment, the OCP of the anode was monitored

32
when MR-1 was added to the anode compartment. The monitoring of the OCP
a
was
started about 2 hours prior to the addition of MR-1 culture to the anode compartment.
The change of OCP
a
during MR-1 addition to the anode compartment is shown in Fig.
1.7. A very stable OCP
a
was observed before the addition of MR-1. After the addition of
MR-1 to the anode compartment, the OCP
a
decreased rapidly which is probably due to
the immediate attachment of the bacterial cells to the graphite felt electrode. The OCP

values attained a stable value within 2 hours after the inoculation with MR-1.

Fig 1.7: Time dependence of the OCP of the anode before and after adding MR-1 to the
anode compartment.

EIS at an applied potential:
In addition to the measurement of the impedance spectra of the anode and cathode at their
corresponding OCPs (Fig. 1.4), impedance measurements were also performed at
different applied potentials, E
app
for the anode and the cathode with two different anolytes.

33
The impedance spectra collected at E
app
for the anode and the cathode with buffer and
lactate and with buffer, lactate and MR-1 as anolytes are shown in Fig. 1.8 and Fig. 1.9
respectively. The fit parameters of these spectra are shown in the Table 1.2 along with the
fit parameters of the impedance spectra of the anode and cathode measured at their
corresponding OCPs. With buffer and lactate as the anolyte, there was very little change
of R
p
of the anode as the electrode was polarized. However, in the presence of MR-1 in
the anode compartment, R
p
a
at an applied potential is significantly lower than the R
p
of
the anode at is OCP.

Fig 1.8: Impedance spectra of the graphite felt anode with buffer and lactate as the
anolyte and the cathode at different applied potentials.

-3 -2 -1 0 1 2 3 4 5
-1
0
1
2
3
4
5
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
EIS of MFC with Electrolyte and Lactate at an applied Potential
Anode Ecorr=0.059
Cathode Ecorr=0.381

-3 -2 -1 0 1 2 3 4 5
-1
0
1
2
3
4
5
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
EIS of MFC with Electrolyte and Lactate at an applied Potential
Anode Ecorr=0.059
Cathode Ecorr=0.381
Anode
Cathode

-3 -2 -1 0 1 2 3 4 5
-1
0
1
2
3
4
5
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
EIS of MFC with Electrolyte and Lactate at an applied Potential
Anode Ecorr=0.059
Cathode Ecorr=0.381

-3 -2 -1 0 1 2 3 4 5
-1
0
1
2
3
4
5
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
EIS of MFC with Electrolyte and Lactate at an applied Potential
Anode Ecorr=0.059
Cathode Ecorr=0.381
Anode
Cathode

34
R
p
of the anode in the MFC is inversely proportional to the rate of the lactate oxidation
reaction talking place on the anode. The results in Table 1.2 indicate that the rate of
oxidation of lactate was much higher when MR-1 was present in the anolyte.
-3 -2 -1 0 1 2 3 4 5
-1
0
1
2
3
4
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
Anode at Eapplied=-0.383V
Cathode at Eapplied=33mV

Fig 1.9: Impedance spectra of the anode with buffer, lactate and MR-1 and the cathode at
different applied potentials

The impedance spectra shown in Fig. 1.4 provide an understanding of the properties of

35
the electrodes at their equilibrium state. The data in Fig. 1.8 and 1.9 provide information
about the kinetics of lactate oxidation reaction in the two different anolytes.
Table 1. 2: Comparison of the fit parameters of the impedance spectra of the anode at an
applied potential and at its OCP with different anolytes.

A1 A2 Electrode
Parameter OCP E
app
OCP E
app

R
p
(Ohms) 5.69 X10
4
6.73 X10
4
3.63 X 10
3
2.1X10
3

C (F) 2.21 X10
-3
2.4 X10
-3
2.42 X10
-3
2.2 X10
-3

Cyclic Voltammetry of the anode in different anolytes:
The cyclic voltammograms generated for the anolyte containing buffer only in Fig. 1.10a
showed no significant peaks. However, a reduction peak at about – 0.25 V and an
oxidation peak at about 0.20 V were observed when the test was performed with buffer
and lactate as the anolyte (Fig. 1.10a).

The CV obtained when the anolyte contained buffer, lactate and MR-1 (Fig. 1.10b) was
significantly different from the CVs obtained for the other two anolytes. The current
passing through the anode was much higher, and a reduction peak was observed at about
–0.50 V, while the oxidation peak was observed to be at the same potential of about 0.20
V as observed in Fig. 1.10a. The peaks observed in Fig. 1.10b are assumed to be due to
several electrochemically active outer membrane cytochromes that are present in MR-1.

36
-400
-300
-200
-100
0
100
200
300
-1000 -500 0 500 1000
E (mV)
I (
μ μ μ μA)
Buffer only Buffer and lactate
a)

-2000
-1500
-1000
-500
0
500
1000
1500
2000
-1000 -500 0 500 1000
E (mV)
I (μ μ μ μA)
b)

Fig 1.10: Cyclic voltammograms for the anode for tests with buffer only and with buffer
and lactate (a) and for test with buffer, lactate and MR-1 (b).

Polarization behavior of the anode and cathode in a MFC:
The polarization curves for the anode containing buffer, lactate and MR-1 as the
electrolyte and for the cathode in the potential region -30mV < OCP <+30mV are shown

37
in Fig. 1.11 a and b, respectively. As discussed by Mansfeld (Mansfeld 2005) an
accurate determination of R
p
and Tafel slopes can be performed by computer analysis of
polarization curves obtained in the vicinity of E
corr
. The polarization curves were
analyzed by fitting the experimental data to the eq.:
I = I
o
(exp(E-E
o
/b
a
) – exp(E
o
-E/b
c
)) (5)

Fig 1.11: Polarization curves of the MFC anode with buffer, lactate and MR-1 as the
anolyte (a), and of the cathode (b).

-1.5
-1
-0.5
0
0.5
1
1.5
2
-30 -20 -10 0 10 20 30 40 50
E-Ecorr (mV)
I (
μ μ μ μA)
a)
- Measured
- Fit
-1.5
-1
-0.5
0
0.5
1
1.5
2
-30 -20 -10 0 10 20 30 40 50
E-Ecorr (mV)
I (
μ μ μ μA)
a)
- Measured
- Fit
-60
-40
-20
0
20
40
60
-40 -30 -20 -10 0 10 20 30 40
E-Ecorr (mV)
I (
μ μ μ μA)
b)
- Measured
- Fit
-60
-40
-20
0
20
40
60
-40 -30 -20 -10 0 10 20 30 40
E-Ecorr (mV)
I (
μ μ μ μA)
b)
- Measured
- Fit

38
These polarization curves were analyzed using the POLFIT program developed by Shih
and Mansfeld (Shih and Mansfeld 1992). From this analysis, the exchange current density
(i
0
), the anodic Tafel slope (b
a
) and the cathodic Tafel slope (b
c
) can be determined. R
p

and i
o
are related by i
o
= B/ R
p
, where B = b
a
b
c
/2.303(b
a
+ b
c
).

A comparison of the experimental and fitted polarization data is also shown in Fig. 1.11.

Experiments were also performed for the anode with buffer only and with buffer and
lactate as the anolytes. The results of the analysis using POLFIT are given in Table 1.3.
The presence of MR-1 in the anolyte increased the value of i
o
by a factor of about 10,
whereas i
o
had similar values in anolytes not containing MR-1.

Table 1. 3: Results of analysis of polarization curves with the POLFIT program.
Test condition I
0
(μA) b
a
(mV) b
c
(mV)
Anode- With
buffer only
0.024 75 44
Anode- With
buffer and
lactate
0.021 106 25
Anode with
buffer, lactate
and MR-1
0.185 43 30
Cathode 19.4 91 61

The results of the polarization experiments performed in a larger potential range shown in
Fig. 1.12 indicate that OCP
a
became much more negative after the addition of MR-1 to

39
the anode compartment as indicated previously in the results obtained in the recording of
EIS data (Fig. 1.4). The polarization curves for tests with the anolyte containing buffer
only and buffer and lactate did not show much difference, however the oxidation currents
that were observed when the anode compartment contained MR-1 were much higher
compared to the other conditions. The cathodic polarization curves for the anode were
similar for the different anolytes.

-1.5
-1
-0.5
0
0.5
1
1.5
-3 -2 -1 0 1 2 3 4 5
Log I (I in μA)
E (V)
1) Anodic and cathodic polarization of the anode
(buffer only)
2) Anodic and cathodic polarization of the
anode (buffer and lactate)
3) Anodic and cathodic polarization of the
anode (buffer, lactate and MR1)
4) Cathodic polarization of the cathode
(buffer only)
1 2 3
4
-1.5
-1
-0.5
0
0.5
1
1.5
-3 -2 -1 0 1 2 3 4 5
Log I (I in μA)
E (V)
1) Anodic and cathodic polarization of the anode
(buffer only)
2) Anodic and cathodic polarization of the
anode (buffer and lactate)
3) Anodic and cathodic polarization of the
anode (buffer, lactate and MR1)
4) Cathodic polarization of the cathode
(buffer only)
1 2 3
4

Fig 1.12: Polarization curves for the anode in three different anolytes and for the cathode
in buffer solution.

Τhe cathodic polarization curve for the cathode intersects the anodic polarization curve
for the anode with anolyte containing buffer, lactate and MR-1 at about 100 μA, as

40
compared to an intersection at less than 1 μA for the other two conditions (Fig. 1.12).
From these data it is apparent that 100 μA is the maximum current that can be drawn
from the MFC used in this study.
1.4.2 Cell Voltage – Current and Power - Time Characteristics of the MFC

Fig. 1.13a shows the cell voltage – current (V-I) curve for the graphite felt anode MFC
with buffer and lactate as the anolyte.
0
50
100
150
200
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18
Current (μ μ μ μA)
Cell Voltage (mV)
a)

0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0 20 40 60 80 100 120 140 160 180
Cell voltage (mV)
Power ( μ μ μ μW)
b)
V
o
V
max
V
1
V
sc

Fig 1.13: V-I (a) and P-V (b) curves for the MFC with graphite felt anode with buffer and
lactate as the anolyte.

41
The open-circuit cell voltage (V
o
) was found to be 0.156V. A maximum current, I
max
of
0.17μA was measured at the short- circuit cell voltage, V
sc
.

The power – cell voltage curve calculated from the V - I curve is shown in Fig. 1.13b. It
is observed that the cell voltage V
max
at which maximum power was obtained was 80 mV.
The maximum power that was obtained from this cell was found to be 6nW. From this P-
V curve, the cell voltage V
1
at which half the maximum power is obtained was found to
be 0.045V. The cell voltages V
0
, V
max
, V
1
and V
sc
are indicated in the Fig. 1.13b.

The V-I curve for the graphite felt MFC with buffer, lactate and MR-1 as the anolyte is
shown in the Fig. 1.14a. V
o
had increased from 0.156V to 0.844V after the addition of
MR-1 to the anolyte which is mostly due to the large decrease of the OCP of the anode.

The maximum current that passed through the cell was 104μA which was much higher
than the maximum current that was obtained in the absence of MR-1 in the anolyte (Fig.
1.13). The value of I
max
obtained from this method agrees well with the intersection of the
polarization curves of the anode and the cathode shown in Fig. 1.12.

42
0
200
400
600
800
1000
0 20 40 60 80 100 120
Current (μ μ μ μA)
Cell Voltage (mV)
a)

0
5
10
15
20
25
0 200 400 600 800 1000
Cell Voltage (mV)
Power (
μ μ μ μW)
b)

Fig 1.14: V- I (a) and P-V (b) curves of the MFC with graphite felt anode with buffer,
lactate and MR-1 as the anolyte.

The P-V curve in Fig. 1.14b shows that in the presence of MR-1, P
max
had increased to
23μW at V
max
= 0.430V. From this P-V curve, the cell voltage V
1
at which half the
maximum power is obtained was found to be 0.130V.

43
An impedance spectrum of the anode and cathode was measured before and after the
measurement of the V-I curves to ensure that polarization of the electrodes in a wide
range of potentials did not result in deterioration of the properties of the electrodes. The
impedance spectra of the anode and cathode measured at their corresponding OCPs
before and after the polarization experiment are shown in Fig. 1.15. The fit parameters of
the spectra are shown in Table 1.4. No significant changes in the properties of the
electrode as a result of polarization during the measurement of the V-I curves were
observed.

Table 1. 4: Comparison of electrode properties before and after the potential sweep
experiment shown.

Anode Cathode
Before
Polarization
After
Polarization
Before
Polarization
After
Polarization
OCP (V) -0.449 -0.450 -0.267 -0.266
R
p
(Ohm) 5.01X10
3
4.77X10
3
3.16X10
3
3.44X10
3

C (F) 2.4X10
-3
2.12 X10
-3
5.8 X10
-2
6.1X10
-3

44
-3 -2 -1 0 1 2 3 4 5
-1
0
1
2
3
4
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
Anode before potential sweep, OCP= -0.449V
anode after potential sweep, OCP= -0.450V
Cathode before potential sweep, OCP= 0.267V
Cathode after potential sweep, OCP= 0.266V

Fig 1.15: EIS data for the anode and the cathode for tests with buffer, lactate and MR-1
before and after measurement of V-I curve

Power-time curves:
Power-time (P-t) curves were generated for both anolyte conditions A1 and A2 with an

45
applied cell voltage and also with a resistor connected between the anode and cathode.
For buffer and lactate as the anolyte the experiment was performed by operating the cell
at a constant cell voltage V
max
corresponding to P
max
from the potential sweep data (Fig
1.13 and 1.14). The power output of the MFC rapidly decreased to values between 20
and 10 nW and continued to decrease slowly during the 12 hour evaluation (Fig. 1.16). A
second P-t curve was generated for the same anolyte condition by operating the MFC
using a 1 Mohm resistor placed between the anode and cathode (Fig. 1.16). The
magnitude of the resistor was calculated according to the procedure explained in the
experimental section. The power output using the external load continued to decrease
slowly over the 12h test period and remained at slightly lower levels than when a
constant cell voltage was applied (Fig. 1.16).

Fig 1.16: P-t curves for the graphite felt MFC with buffer and lactate as the anolyte using
an applied cell voltage or an external resistor.
0
50
100
0 2 4 6 8 10 12
Time (Hours)
Power (nW)
V=200mV
R=1Mohm
V
max
R
ext
0
50
100
0 2 4 6 8 10 12
Time (Hours)
Power (nW)
V=200mV
R=1Mohm
V
max
R
ext

46

The P-t curves generated after the addition of MR-1 using an applied cell voltage and an
external resistance of 4 Kohm are shown in Fig. 1.17. By comparing the results in Fig.
1.16 and Fig. 1.17, it is apparent that the addition of MR-1 to the anode increased the
power production by several orders of magnitude. Additionally, for the tests with the
external resistance, the MFC with MR-1 in the anolyte achieved stable power production
within one hour of MFC operation for both conditions (Fig. 1.17), whereas the MFC
without MR-1 (R = 1 Mohm) did not stabilize until over 12 hours of operation (Fig. 1.16).

0
5
10
15
20
25
30
35
40
45
50
0 2 4 6 8 10 12
Time (Hours)
Power (
μ μ μ μW)
External Resistor
Vmax

Fig 1.17: P-t curves for the graphite felt MFC with buffer, lactate and MR-1 as the
anolyte using an applied cell voltage and a constant external resistor.

47
1.4.3 Performance of the MFC over Extended Periods of Operation

Figs 1.18 and 1.19 show the time dependence of the OCP of the anode and R
p
of the
anode with different anolytes during 16 days of operation of a MFC. During this period,
various experiments including the measurement of V-I curves, measurements of
impedance spectra of the electrodes at their OCP and at an applied potential and power –
time curves were performed. During the sixteen day period, lactate was periodically fed
to the anode compartment as the fuel for MR-1. These feedings are denoted as feed 1 to 4
in the following discussion.

The OCP data in Fig. 1.18 illustrate the drastic decrease of the OCP
a
upon addition of
MR-1. While OCP
a
had values between 0 and 0.2 V in the absence of MR-1 (Fig. 1.18),
it decreased to values between –0.4 and –0.5 V in the presence of MR-1. The OCP values
were found to be very stable for both anolyte conditions. It was also observed that the
OCP of the anode returns to its normal value even after an experiment at an applied
potential (indicated by arrows in the Fig. 1.18).

In Fig. 1.19 a comparison is given of the R
p
values obtained over extended time periods
for the anode with buffer only or buffer and lactate as anolytes. Measurements with
buffer, lactate and MR-1 are also shown with four feeds of lactate over the sixteen day
operation in Fig. 1.19. The R
p
values obtained from the impedance measurements that
were performed at an applied potential is indicated by an arrow in the plot.

48

Fig 1.18: Time dependence of the OCP of the anode with different anolytes (arrow marks
indicate tests at an applied potential).

The R
p
values for the anode decreased markedly upon polarization to about the same
value in all four tests (Fig. 1.19). This result indicates that the rate of lactate oxidation
taking place at the anode is considerably increased at an applied potential. It was also
observed that the extent of decrease in the R
p
of the anode at an applied potential is more
significant when MR-1 is present in the anolyte. This suggests that the oxidation of
lactate is not possible in the absence of MR-1 in the anode compartment. This result
agrees well with the information presented by the data in Fig. 1.8 and Fig. 1.9. The R
p

values of the anode however returned back to the values determined before polarization
after about four hours. These results demonstrate again that the electrode properties
remained more or less unchanged at their respective OCPs during the entire test period
-0.6
-0.4
-0.2
0
0.2
0.4
0 10 20 30 40 50
Time hours
OCP (V)
Feed 1
Feed 2
Feed 3
Feed 4
Buffer
Only
Buffer and
lactate
a)
-0.6
-0.4
-0.2
0
0.2
0.4
0 10 20 30 40 50
Time hours
OCP (V)
Feed 1
Feed 2
Feed 3
Feed 4
Buffer
Only
Buffer and
lactate
a)

49
despite occasional polarization.

Fig 1.19: Time dependence of R
p
of anode with different anolytes (arrow marks indicate
tests at an applied potential).

In order to better understand the long term power production of the MFC, further
inspection of the V-I curves and P-t curves was performed in the presence of MR-1 for a
period of sixteen days (Fig. 1.20).

The cell voltage remained between 600 mV to 700mV throughout the period, but the
maximum current began to decrease after the second feeding of lactate to the anode
compartment and fell to about 80 μA after the last lactate addition.
2
2.5
3
3.5
4
4.5
5
5.5
6
0 5 10 15 20 25 30 35 40 45
Time Hours
Log Rp (Rp in Ohm)
Feed 1 Feed 2 Feed 3
Feed 4 Buffer only Buffer and lactate
2
2.5
3
3.5
4
4.5
5
5.5
6
0 5 10 15 20 25 30 35 40 45
Time Hours
Log Rp (Rp in Ohm)
Feed 1 Feed 2 Feed 3
Feed 4 Buffer only Buffer and lactate

50

Fig 1.20: V-I (a) and P-V curves (b) for tests with buffer, lactate and MR-1 over a 16 day
period

51
The maximum power output of the MFC initially increased to 25 μW and then decreased
to 15 μW at day 16 (Fig. 1.20).

P–t curves were also measured during this period by applying the cell voltage V
max
at
which maximum power was obtained or by connecting a resistor whose magnitude is
calculated using Ohm’s law using the value of V
max
and the current measured at V
max

determined from the V-I curve. The P-t curves at an applied cell voltage measured after
every lactate feed are shown in Fig. 1.21. The measurement with an external resistor was
performed for feeds 2, 3 and 4 (Fig. 1.22).

Fig 1.21: P-t curves for tests with buffer, lactate and MR-1 at constant cell voltage V
max
.
0 4 8 12
Time (hours)
0
10
20
30
40
50
Power (μW)
Feed , V=300mV
Feed 2, V=400mV
Feed 3, V=300mV
Feed 4, V=350mV
Feed 5, V=350mV
Feed 1
Feed 2
Feed 3
Feed 4
Feed 5
0 4 8 12
Time (hours)
0
10
20
30
40
50
Power (μW)
Feed , V=300mV
Feed 2, V=400mV
Feed 3, V=300mV
Feed 4, V=350mV
Feed 5, V=350mV
Feed 1
Feed 2
Feed 3
Feed 4
Feed 5
0 4 8 12
Time (hours)
0
10
20
30
40
50
Power (μW)
Feed , V=300mV
Feed 2, V=400mV
Feed 3, V=300mV
Feed 4, V=350mV
Feed 5, V=350mV
Feed 1
Feed 2
Feed 3
Feed 4
Feed 5

52

Fig 1.22: P-t curves for tests with buffer, lactate and MR-1 with resistor connected

1.4.4 Characterization of the Stainless Steel Ball Packed Bed Anode

EIS Results
The Bode plot of the impedance spectra for the anode in the MFC with the SS ball
packed bed electrode with buffer and lactate as anolyte is shown in Fig. 1.23. It was
found that the impedance spectrum corresponds to a two-time constant model behavior.
The impedance spectrum of the graphite felt anode measured in the same anolyte is also
shown in Fig. 1.23 for comparison. OCP
a
for the SS packed bed anode was 44mV which
is much lower than the OCP of the graphite felt anode that was measured in the same
anolyte (Fig. 1.23).

53
-3 -2 -1 0 1 2 3 4 5
0
1
2
3
4
5
6
SS Ball packed bed anode. OCP = 44mV
Graphite felt anode. OCP= 0.197V
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0

Fig 1.23: Bode-plots for the SS ball packed bed anode with buffer and lactate as the
anolyte.

The addition of SS balls to the anode compartment increases the capacitance of the anode
and decreased the polarization resistance which suggests that the increase in the electrode
surface area caused by the addition of SS balls to the anode compartment has increased

54
both the active surface area of the anode and has increased the rate of redox reaction
occurring at the electrode surface.
-3 -2 -1 0 1 2 3 4 5
0
1
2
3
4
5
SS ball packed bed anode. OCP = -0.512V
Graphite felt anode. OCP = -0.491V
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0

Fig 1.24: Bode plots of the SS ball packed bed anode with buffer, lactate and MR-1 as the
anolyte.

55
The impedance spectra of the anode with the SS packed bed anode and the graphite felt
anode with buffer, lactate and MR-1 as the anolyte is shown in Fig. 1.24. After the
addition of MR-1 to the anode compartment, OCP
a
decreased to -512mV which is lower
than the OCP of the graphite felt anode (-0.491V).

The impedance spectra of the anode with SS balls packed bed anode showed a two-time
constant behavior and the low-frequency behavior of the impedance spectra indicated that
R
p
of the anode had decreased considerably after the addition of MR-1 to the anode
compartment. This decrease of R
p
together with a decrease in the OCP of the anode
suggests an increase in the exchange current density, i
0
of the redox reaction taking place
in the anode compartment in the presence of MR-1 (Mansfeld 2006a).

Fig 1.25: Equivalent circuit corresponding to the impedance response of the SS ball
packed bed anode with different anolytes.

The impedance spectra of the SS ball packed bed anode (Fig. 1.23 and 1.24) with
different anolytes (A1 and A2) were analyzed using the two-time constant model shown
in Fig. 1.25 and the ANALEIS software (Mansfeld et al. 1992; Mansfeld et al. 1993;
R
1
R
2
C
1 C
2

56
Mansfeld 2006b). In the equivalent circuit, R
1
and

C
1
correspond to the polarization
resistance and capacitance of the SS packed bed electrode while R
2
and C
2
correspond to
the polarization resistance and the capacitance of the graphite felt feeder electrode. The
fit-parameters of the impedance spectra for the anode are listed in Table 1.5.

R
s
represents the solution and ohmic resistances of the anolyte and the anode electrode.
This value is found to be slightly higher than R
s
of the graphite felt anode (Table 1.1).
This can be explained by considering the volume of the anolyte in the anode
compartments of the SS ball MFC and the MFC with the graphite felt anode. The
graphite felt MFC has more volume of anolyte than the SS ball MFC which results in its
lower solution resistance.
Table 1. 5: Fit parameters for the impedance spectra of the graphite/SS ball anode for
anolytes A1 and A2.
Fit Parameter A1 A2
R
1
(Ohm) 5.99X10
2
1.65X10
2

R
2
(Ohm) 1.44X10
6
1.72X10
4

C
1
(F) 1.62X10
-2
6.45X10
-3

C
2
(F) 1.72X10
-1
7.5X10
-2

R
s
(Ohm) 9.2 8.2

For the MFC with SS balls in the anode compartment, R
p
of the anode can be defined as
R
p
a
= R
1
+ R
2
. R
1
decreased only slightly upon addition of MR-1 to the anode
compartment whereas a very large decrease of R
2
was observed (Table 1.5). The small

57
decrease in R
1
could be due to MR-1 not forming an efficient biofilm on the surface of
the SS packed bed electrode. However, a good biofilm could be forming on the surface of
the graphite felt feeder electrode and hence a large decrease in R
2
with the addition of
MR-1 was observed.

For both anolytes, it was observed that R
1
was much smaller than R
2
which could be due
to the higher electrode surface area of the SS ball packed bed electrode. No significant
changes in C
1
and C
2
were observed when MR-1 was added to the anolyte.

1.4.5 Cell Voltage – Current Characteristics of the MFC with SS Ball Packed Bed
Anode

Fig. 1.26a shows the V-I curve for the MFC with SS balls in the anode compartment with
buffer and lactate as the anolyte. The open-circuit cell voltage (V
o
) was 300 mV.

The maximum current measured at short- circuit (I
sc
) was about 8μA which was about 50
times larger than I
sc
obtained for the MFC without SS balls (Fig. 1.13). The P-V curve in
the Fig. 1.26b indicates that a maximum power of 0.4μW was obtained at a cell voltage
V
max
of 150mV compared to the 0.006 μW obtained for the MFC without SS balls (Fig.
1.13b) using the same anolyte. From the P-V curve, V
1
was found to be 0.025V (Fig
1.26b).

58
0
50
100
150
200
250
300
350
0 2 4 6 8 10
Current (μ μ μ μA)
Cell Voltage (mV)
a)
0
0.1
0.2
0.3
0.4
0.5
0 50 100 150 200 250 300 350
Cell Voltage (mV)
Power ( μ μ μ μW)
b)

Fig 1.26: V- I (a) and P-V (b) curves of the MFC with a SS ball packed bed anode with
buffer and lactate as the anolyte.

After the addition of MR-1 to the anode compartment, V
o
increased to about 880 mV and
I
sc
increased to 120 μA (Fig. 1.27a) which is much higher than I
max
obtained without MR-
1 (Fig 1.26a). I
max
obtained from this configuration was slightly higher than the
maximum current obtained without SS balls in the anode compartment with the same
anolyte. The maximum power P
max
= 26 μW was obtained at a cell voltage V
max
of 470

59
mV (Fig. 1.27b) which is similar to P
max
obtained in the absence of the SS balls (Fig.
1.14b). From the P-V curve, V
1
was found to be 125mV.
0
100
200
300
400
500
600
700
800
900
1000
0 20 40 60 80 100 120 140
Current (μ μ μ μA)
Cell Voltage (mV)
0
5
10
15
20
25
30
0 200 400 600 800 1000
Cell Voltage (mV)
Power (
μ μ μ μW)

Fig 1.27: V- I and P-V curves of the MFC with SS ball packed bed anode with buffer,
lactate and MR-1 as the anolyte.

1.4.6 Analysis of the Internal Resistance of the MFC

Fig. 1.28 shows the impedance spectra for the MFC that were obtained at the four
different applied cell voltages V
o
, V
max
, V
1
, and V
sc
with buffer and lactate as the anolyte
using a two-electrode technique.
a)
b)

60

-3 -2 -1 0 1 2 3 4 5
0
1
2
3
4
5
6
At V
o
At V
max
=0.075V
At V
1
=0.045V
At V
sc
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0

Fig 1.28: Bode plots for the MFC with graphite felt anode at different cell voltages with
buffer and lactate as the anolyte.

The solution resistance R
cell
s
of the MFC was higher than R
s
for the anode and cathode
since it includes the resistance of the anolyte and catholyte between the anode and the
cathode (R
Ω
) and the resistance of the membrane (R
m
.).

61
EIS data obtained for the MFC in the presence of MR-1 at four different applied cell
voltages are shown in the Fig. 1.29. The low-frequency dependence of the impedance
spectra indicates that R
cell
p
of the MFC decreased significantly as the applied cell voltage
decreased, i.e. the cell current increased.

-3 -2 -1 0 1 2 3 4 5
0
1
2
3
4
5
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
At V
o
=0.844V
At V
max
=0.430V
At V
1
=0.130V
At V
sc
.

Fig 1.29: Bode plots for the MFC with graphite felt anode at different cell voltages with
buffer, lactate and MR-1 as the anolyte.

62
A comparison of the spectra in Fig. 1.28 and 1.29 demonstrates that the decrease of
impedance in the low-frequency region with increase of the applied cell voltage was
more significant in the presence of MR-1.

The fit-parameters of the impedance spectra shown in Fig. 1.28 and Fig. 1.29 are
tabulated in Table 1.6 and 1.7 respectively. The polarization resistance (R
p
cell
) of the
MFC under investigation was defined as
R
p
cell
= R
a
p
+ R
c
p
+ R
Ω
+ R
m
, (6)

where R
Ω
and R
m
are the resistances of the electrolyte between the two electrodes and the
membrane resistance, respectively and R
cell
s
= R
Ω
+ R
m
. The previous equation then
becomes
R
p
cell
= R
a
p
+ R
c
p
+ R
cell
s
,

As can be seen from Tables 1.6 and 1.7, R
cell
s
<< R
a
p
+ R
c
p
and therefore, R
p
cell
= R
p
a
+R
p
c
.
From this we can write, R
int
= R
p
cell
(7)

63
Table 1. 6: Fit parameters for EIS data obtained at different applied cell voltages (anolyte:
buffer and lactate).

Parameter V
o
V
max
V
1
V
sc

R
p
cell
(Ohm) 9.79X10
6
2.94X10
6
1.50X10
6
5.23X10
5

C
cell
(F) 7.11*10
-4
7.28*10
-4
8.33*10
-4
1.03*10
-3

R
s

cell
(Ohm) 14.6 14.6 14.7 14.2

Table 1. 7: Fit parameters for EIS data obtained at different applied cell voltages (anolyte:
buffer, lactate and MR-1).

Parameter V
o
V
max
V
1
V
sc

R
p
cell
(Ohm) 7.20*10
4
9.81*10
3
7.24*10
3
4.58*10
3

C
cell
(F) 7.84*10
-4
9.24*10
-4
9.13*10
-4
7.11*10
-4

R
s

cell
(Ohm) 14.2 13.4 12.8 11.7

R
p
cell
(R
int
) decreased in both the anolytes as the applied cell voltage decreased. This is
due to the increase of the rates of lactate oxidation taking place at the anode and oxygen
reduction at the cathode as the cell current increases.

The capacitance values C
cell
in Tables 1.6 and 1.7 contain contributions from the
capacitance of the anode as well as the capacitance of the cathode. This capacitance
values show very little variation with applied cell voltage for tests in both anolytes. The
capacitance values shown in Tables 1.6 and 1.7 are numerically close to the capacitance
of the anode shown in Table 1.1. When measuring the impedance spectra of the MFC, the

64
impedance of the anode and cathode are in a series combination. The equivalent circuit
(EC) of the MFC is represented by a the polarization resistance and the capacitance of the
anode and cathode in series. When measuring the impedance spectra of the cell, which
has two capacitors in series combination, the lower capacitance will dominate. Since the
capacitance of the anode is lower than the capacitance of the cathode (Table 1.1), it
dominates the total capacitance of the MFC. The solution resistance R
cell
s
observed in the
high-frequency region of the impedance spectra shown in Fig. 1.28 and 1.29 is the sum of
the resistances of the anolyte and the catholyte and the resistance of the membrane (R
cell
s

= R
Ω
+ R
m
). From Table 1.6 and 1.7 it can be observed that R
cell
s
did not change
significantly with applied cell voltage.

In order to obtain an estimate of the experimental value of the membrane resistance R
m

the potential difference between two references electrodes placed on both sides of the
membrane in the anode and cathode compartment while a current was flowing through
the cell were measured at V
max
, V
1
and V
sc
for three hours in buffer, lactate and MR-1
anolyte. The potential difference at zero current flow was monitored for 30 min. (Fig.
1.30a) before the appropriate cell voltage was applied between the anode and the cathode.
Fig. 1.30a shows the potential difference data, while Fig. 1.30b shows the current – time
curves. The potential difference ΔE in the absence of current flow is due to small
differences in the potential of the two Ag/AgCl reference electrodes. It increases as a cell
voltage is applied between the anode and cathode because of the contributions of the
resistance of the electrolyte between the two reference electrodes (R’
Ω
) and R
m
.

65
-3
-2
-1
0
1
2
0 0.5 1 1.5 2 2.5 3 3.5 4
Time (hours)
Δ Δ Δ Δ E (mV)
a)
1
2
3
1- V
max
, 2- V
1
, 3- V
sc

0
20
40
60
80
100
120
0 0.5 1 1.5 2 2.5 3 3.5
Time (Hours)
Current ( μ μ μ μ A)
b)
1
2
3
1- V
max
, 2- V
1
, 3- V
sc

Fig 1.30: .E – t (a) and I-t (b) curves at three different cell voltages with buffer, lactate
and MR-1 as the anolyte.

Table 1. 8: Variation of Rm + R
Ω
' with applied cell voltage.
Applied cell
voltage
R
m

+ R
Ω
'

(Ohm)
V
max
5.85
V
1
5.40
V
sc
3.52

This resistance value R’
Ω
+ R
m
was calculated based on the potential difference in the

66
absence and presence of current flow (Fig. 1.30a) and the value of the current at the end
of the test (Fig. 1.30b). The results of these calculations in Table 1.8 demonstrate that
R’
Ω
+ R
m
decreased slightly with increasing current and was very small compared to R
int
.

Impedance spectra recorded in anolyte A1 for the MFC with stainless steel balls in the
anode compartment at four applied cell voltages as shown in Fig. 1.31. These spectra
show a two-time constant behavior. No significant change in the impedance spectra
occurred as the applied cell voltage is decreased. With anolyte A2 (Fig. 1.32), the
impedance spectra of the cell measured at various cell voltages also showed a two-time-
constant behavior. However, in A2, as the applied cell voltage was decreased, a very
marked change in the low-frequency behavior of the phase angle was observed.

67

-3 -2 -1 0 1 2 3 4 5
0
1
2
3
4
5
6
At V
o
At V
max
=0.150V
At V
1
=0.025V
At V
sc
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0

Fig 1.31: Bode plots for the MFC with SS ball packed bed anode at different cell voltages
with buffer and lactate as the anolyte.

68
-3 -2 -1 0 1 2 3 4 5
0
1
2
3
4
5
6
Cell at V
0

Cell at V
max
=0.470V
Cell at V
1
=0.125V
Cell at V
sc

-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0

Fig 1.32: Bode plots for of the MFC with SS ball packed bed anode at different cell
voltages with buffer, lactate and MR-1 as the anolyte.

The fit-parameters of the impedance spectra of the cell measured at four different cell
voltages are shown in Fig. 1.33 for both anolytes. For this MFC, R
p
cell
has contributions
from the graphite anode, SS balls, the platinum plated graphite cathode, the electrolytes
present in the anode and cathode compartment and the membrane. R
p
cell
can be

69
determined from the fit parameters as follows. R
p
cell
= R
1
+R
2
. R
p
cell
of the cell decreases
by a factor of 50 after the addition of MR-1 to the anode compartment.

Fig 1.33: (a) R
1
and R
2
and (b) C
1
and C
2
for MFC with SS balls at four different applied
cell voltages and two different anolytes.

The dependence of R
int
on cell voltage is shown in Fig. 1.34a for the two different
anolytes and the MFC with and without SS balls. In all cases R
int
decreased as the
applied cell voltage was decreased. For buffer and lactate as anolyte R
int
showed a very
1.00E+00
1.00E+02
1.00E+04
1.00E+06
1 2 3 4
Applied Cell voltage (V)
Log R3, R4 (R in Ohm)
R3 (A1) R4 (A1) R3 (A2) R4 (A2)
Vo Vmax V1
Vsc
a)
Log R1 and R2 (R in Ohm)
R1 R2 R1 R2
1.00E+00
1.00E+02
1.00E+04
1.00E+06
1 2 3 4
Applied Cell voltage (V)
Log R3, R4 (R in Ohm)
R3 (A1) R4 (A1) R3 (A2) R4 (A2)
Vo Vmax V1
Vsc
a)
Log R1 and R2 (R in Ohm)
R1 R2 R1 R2
0
0.01
0.02
0.03
0.04
1 2 3 4
Applied Cell Voltage
C3, C4 (F)
C3 (A1) C4 (A1) C3 (A2) C4 (A2)
Vo Vmax V1 Vsc
b)
C1 C2 C1 C2
C1 and C2 (F)
0
0.01
0.02
0.03
0.04
1 2 3 4
Applied Cell Voltage
C3, C4 (F)
C3 (A1) C4 (A1) C3 (A2) C4 (A2)
Vo Vmax V1 Vsc
b)
C1 C2 C1 C2
C1 and C2 (F)

70
large decrease when the SS balls were added to the anode compartment (curves 1 and 3).
R
int
also decreased significantly when MR-1 was added to the anolyte (curves 1 and 2).
When SS balls were added to the anolyte containing MR-1, a significant decrease in R
int

was not observed as with the case without MR-1 in the anolyte (curves 1 and 3).
1.00E+03
1.00E+05
1.00E+07
0 200 400 600 800 1000
Cell Voltage (mV)
Log Rint (Rint in Ohm)
1
2
3
4
3
5
3
7
3
a)

1.00E-03
1.00E-01
1.00E+01
1.00E+03
1.00E+03 1.00E+04 1.00E+05 1.00E+06
Log R
int
at V
max
Log P max (Pmax in μ μ μ μW)
`
1
2
3
-3
-1
1
3
3
4 5 6
4
b)

Fig 1.34: Dependence of (a) R
int
on cell voltage and (b) P
max
on R
int
for the four cases
studied.

1-Buffer and lactate
2-Buffer, lactate and MR-1
3-Buffer and lactate, SS balls
4-Buffer, lactate and MR-1, SS balls
1-Buffer and lactate
2-Buffer, lactate and MR-1
3-Buffer and lactate, SS balls
4-Buffer, lactate and MR-1, SS balls

71
This result could be explained as follows. When adding SS balls to the anode
compartment without MR-1 in the anolyte, the increase in electrode surface area results
in a considerable increase of the exchange current I
o
of the anodic reaction. However, in
the presence of MR-1 in the anolyte, an efficient biofilm may not be forming on the
surface of the SS balls packed bed and so the R
int
of the cell remains similar to that of the
MFC without SS balls with the same anolyte. The decrease of R
int
leads to large increase
of the maximum power produced by the MFCs containing SS balls without MR-1 in the
anolyte (Fig. 1.34b) and only a slight increase is observed for the MFCs with MR-1.

The finding that R
int
did not decrease much further when MR-1 was added to the anolyte
in the cell containing the SS balls can be understood by an evaluation of the impedance
spectra for the anode and the cathode at their respective OCPs and the MFC at V
o
for the
four cases studied in this investigation (Fig. 1.35 and Fig. 1.36).

Since the impedance of the anode and the cathode are in series, the impedance of the
MFC is the sum of these two impedances. For the cell without SS balls the impedance of
the MFC was very similar to that of the anode even in the presence of MR-1 (Fig. 1.35a
and 1.35b). Therefore R
int
has values that are close to R
a
p
.

72
1.00E+00
1.00E+03
1.00E+06
0.001 1 1000 1000000
log f (f in Hz)
Log Z (Z in Ohm)
Anode Cathode Cell (Measured)
a)
Graphite felt electrode: Anolyte: Buffer and
lactate
6
3
0
6
3 0 -3

1.00E+00
1.00E+03
1.00E+06
0.001 1 1000 1000000
Log f (f in Hz)
Log Z (Z in Ohm)
Anode Cathode Cell (Measured)
b) Graphite anode: Anolyte:Buffer, lactate and MR-1 6
3
0
6 3 0 -3

Fig 1.35: Impedance spectra of the anode and the cathode at their OCP and for the MFC
with graphite felt anode at V
o
with different anolytes.

For the cell with SS balls in the anode compartment R
a
p
and R
int
decreased significantly
(Fig. 1.36a), however R
a
p
was still considerably larger than R
c
p
. A different situation
occured when MR-1 is added to anolyte A1 as shown in Fig. 1.36b. In this case R
a
p
< R
c
p

and any further significant decrease of R
int
would only be possible if the rate of the

73
oxygen reduction reaction could be increased by an improved design of the cathode.

1.00E+00
1.00E+03
1.00E+06
0.001 1 1000 1000000
Log f (f in HZ)
Log Z (Z in Ohm)
Anode Cathode Cell (Measured)
c) Graphite felt/SS balls anode. Anolyte:
Buffer and lactate
6
3
0
6 3 0 -3

1.00E+00
1.00E+03
1.00E+06
0.001 1 1000 1000000
Anode Cell (Measured) Cathode
d)
Graphite Felt/SS balls anode:.
Anolyte: Buffer, lactate and MR-1
6
3
0
6 3 0
-3

Fig 1.36: Impedance spectra of the anode and the cathode at their OCP and for the MFC
with SS balls at V
o
with different anolytes.

a)
b)

74
1.5 Conclusions

The results of this study have demonstrated that the use of a number of different
electrochemical techniques facilitates the complete characterization of the
electrochemical properties of the individual electrodes and of the MFC with different
anolytes and as a function of time. EIS has been used in the following applications: 1) as
a quality control tool to test the properties of fresh electrodes; 2) as a tool to determine
the reaction rates at the anode and cathode at their open circuit potentials and at different
applied potentials; 3) as a tool to monitor possible changes of the electrode properties due
to extensive polarization of the electrodes; and 4) as a tool to monitor important MFC
parameters such as the internal resistance R
int
as a function of cell voltage for different
MFC configurations and operating conditions.

Analysis of the impedance spectra for the anode showed that addition of Shewanella
oneidensis MR-1 to a solution of buffer and lactate greatly increased the rate of the
lactate oxidation at the OCP
a
of the anode. The large decrease of OCP
a
in the presence of
MR-1 increased the cell voltage of the MFC and its power output. The much larger
capacitance of the Pt-plated cathode was due to its much larger active area. The
observation that R
a
p
was much larger than R
c
p
shows that in the present MFC the rate of
oxygen reduction at the cathode is much faster than the rate of lactate oxidation at the
anode.

75
Utilizing a potential sweep technique with a potentiostat to measure V-I curves allows for
the determination of I
max
with greater accuracy than the commonly used step-resistor
method. This technique also yields V-I and P-V curves that can be used to determine the
cell voltage V
max
or the applied resistor at which the MFC should provide maximum
power output. The power output has been monitored over 12 h periods either by applying
V
max
or connecting a resistor between the anode and the cathode that would produce a
similar cell voltage.

Electrochemical tests in the presence of MR-1 were performed for a time period of about
16 days with periodic additions of lactate. While the cell voltage and I
max
values
decreased with time, the overall power output was significantly higher than that found in
measurements without MR-1. The CVs illustrated a large change in the electrochemical
activity of the anode in the presence of MR-1. Oxidation peaks were observed at 200 mV
and -500 mV (vs Ag/AgCl). The anodic polarization curves showed a very large increase
of the anodic (oxidation) current. The intersection of the anodic polarization curve of the
anode and the cathodic polarization curve of the cathode gives a maximum cell current of
about 100 μA. Since this current is less than the limiting current for oxygen reduction on
the cathode, one can conclude that the power output of the present MFC could be
increased by about of factor of 10 if it were possible to increase the anodic current by the
same amount.

EIS has been used to determine the internal resistance R
int
of the MFC as a function of

76
cell voltage for two different anode configurations (with and without stainless steel balls)
and two different anolytes (with and without Shewanella oneidensis MR-1) for four test
series. Measurements of impedance spectra for the MFC at different cell voltages allow
the determination of R
int
which was lower by about a factor 100 in the presence of MR-1
and decreased with decreasing cell voltage since both R
a
p
and R
c
p
decrease with
increasing current flow.

For all test conditions it has been found that R
int
decreased with decreasing V which was
accompanied by an increase of the maximum power P
max
that a given MFC could
produce. The addition of SS balls to the anode compartment increased the active area of
the anode thereby reducing R
a
p
which in turn decreased R
int
.

A comparison of the impedance spectra for the anode and the cathode at their OCP with
the impedance spectrum of the MFC at the open-circuit cell voltage V
o
showed that the
impedance of the cell was dominated by the impedance of the anode except for the case
where SS balls and MR-1 were added to the anode compartment. For the other cases R
c
p

was much lower than R
a
p
due to the presence of the Pt particles on the graphite felt
cathode that greatly enhance the rate of oxygen reduction.

77
1.6 Suggestions for Future Work

The analysis of electrochemical measurements presented in this study provide guidance
for evaluating the properties of the electrodes and the performance of MFCs. In order to
increase the maximum power that can be obtained from a MFC, R
int
needs to be
substantially decreased. The performance of the MFC with the SS packed bed electrode
suggests that in this case the MFC performance is limited by the cathode properties which
could be overcome by using a cathode material which is more catalytically active for the
oxygen reduction reaction. Another method to improve the cathode properties is by using
a different cathodic reaction. Several alternatives for oxygen reduction in a MFC cathode
have been suggested in the literature. The R
int
of the MFC can be measured using the
procedure explained in this study which allows identifying the value of R
int
, its
dependence on cell voltage and the electrode that limits the overall performance of the
MFC.

The significance of the capacitance of the anode obtained from the fitting of the
impedance spectra is not completely understood. In this study, C of the graphite felt
anode did not change even with the addition of MR-1 to the anode compartment. A
systematic study of the anode in a half cell set up with a simple anode design and
different anolyte conditions could be conducted to evaluate the significance of the C
parameter in MFC electrode measurements.

78
1.7 Chapter 1 References

Aaron, D., Tsouris, C., Hamilton, C. Y. and Borole, A. P. (2010). "Assessment of the
Effects of Flow Rate and Ionic Strength on the Performance of an Air-Cathode
Microbial Fuel Cell Using Electrochemical Impedance Spectroscopy." Energies
3(4): 592-606.
Aelterman, P., Rabaey, K., Pham, H. T., Boon, N. and Verstraete, W. (2006).
"Continuous Electricity Generation at High Voltages and Currents Using Stacked
Microbial Fuel Cells." Environmental Science & Technology. 40(10): 3388-3394.
Bennetto, H. P., John, L. S., Kazuko, T. and Carmen, A. V. (1983). "Anodic Reactions in
Microbial Fuel Cells." Biotechnology and Bioengineering 25(2): 559-568.
Bond, D. R., Holmes, D. E., Tender, L. M. and Lovley, D. R. (2002). "Electrode-
Reducing Microorganisms That Harvest Energy from Marine Sediments." Science
295(5554): 483-485.
Bond, D. R. and Lovley, D. R. (2003). "Electricity Production by Geobacter
Sulfurreducens Attached to Electrodes." Appl. Environ. Microbiol. 69(3): 1548-
1555.
Borole, A. P., Aaron, D., Hamilton, C. Y. and Tsouris, C. (2010). "Understanding Long-
Term Changes in Microbial Fuel Cell Performance Using Electrochemical
Impedance Spectroscopy." Environmental Science & Technology 44(7): 2740-
2744.
Bretschger, O. (2008). Electron Transfer Capability and Metabolic Processes of the
Genus Shewanella with Applications to the Optimization of Microbial Fuel Cells,
University of Southern California. PhD Thesis.
Bretschger, O., Cheung, A. C. M., Mansfeld, F. and Nealson, K. H. (2010). "Comparative
Microbial Fuel Cell Evaluations of Shewanella Spp." Electroanalysis 22(7-8):
883-894.

79
Bretschger, O., Obraztsova, A., Sturm, C. A., Chang, I. S., Gorby, Y. A., Reed, S. B.,
Culley, D. E., Reardon, C. L., Barua, S., Romine, M. F., Zhou, J., Beliaev, A. S.,
Bouhenni, R., Saffarini, D., Mansfeld, F., Kim, B. H., Fredrickson, J. K. and
Nealson, K. H. (2007). "Current Production and Metal Oxide Reduction by
Shewanella Oneidensis MR-1 Wild Type and Mutants." Applied and
Environmental Microbiology 73: 7003-7012.
Cai, M., Liu, J. and Wei, Y. (2004). "Enhanced Biohydrogen Production from Sewage
Sludge with Alkaline Pretreatment." Environmental Science & Technology
38(11): 3195-3202.
Chaudhuri, S. K. and Lovley, D. R. (2003). "Electricity Generation by Direct Oxidation
of Glucose in Mediatorless Microbial Fuel Cells." Nat Biotech 21(10): 1229.
Clauwaert, P., Rabaey, K., Aelterman, P., De Schamphelaire, L., Ham, T. H., Boeckx, P.,
Boon, N. and Verstraete, W. (2007a). "Biological Denitrification in Microbial
Fuel Cells." Environmental Science & Technology 41(9): 3354-3360.
Clauwaert, P., van der Ha, D., Boon, N., Verbeken, K., Verhaege, M., Rabaey, K. and
Verstraete, W. (2007b). "Open Air Biocathode Enables Effective Electricity
Generation with Microbial Fuel Cells." Environmental Science & Technology
41(21): 7564-7569.
Cooper, K. R. and Smith, M. (2006). "Electrical Test Methods for on-Line Fuel Cell
Ohmic Resistance Measurement." Journal of Power Sources 160(2): 1088-1095.
El-Naggar, M. Y., Gorby, Y. A., Xia, W., Nealson, K. H., (2008), “The Molecular
Density of States in Bacterial Nanowires”, Biophysical Journal 95(1): L10-L12.
Fan, Y., Hu, H. and Liu, H. (2007). "Enhanced Coulombic Efficiency and Power Density
of Air-Cathode Microbial Fuel Cells with an Improved Cell Configuration."
Journal of Power Sources 171(2): 348-354.
Fricke, K., Harnisch, F. and Schroder, U. (2008). "On the Use of Cyclic Voltammetry for
the Study of Anodic Electron Transfer in Microbial Fuel Cells." Energy &
Environmental Science 1(1): 144-147.
Gomadam, P. M. and Weidner, J. W. (2005). "Analysis of Electrochemical Impedance
Spectroscopy in Proton Exchange Membrane Fuel Cells." International Journal of
Energy Research 29(12): 1133-1151.

80
Gorby, Y. A., Yanina, S., McLean, J. S., Rosso, K. M., Moyles, D., Dohnalkova, A.,
Beveridge, T. J., Chang, I. S., Kim, B. H., Kim, K. S., Culley, D. E., Reed, S. B.,
Romine, M. F., Saffarini, D.A., Hill, E. A., Shi, L., Elias, D. A., Kennedy, D. W.,
Pinchuk, G., Watanabe, K., Ishii, S., Logan, B., Nealson, K. H., Fredrickson, J. K.,
(2006), “Electrically conductive bacterial nanowires produced by Shewanella
oneidensis strain MR-1 and other microorganisms”, PNAS 103(30): 11358-11363.
Gregory, K. B. and Lovley, D. R. (2005). "Remediation and Recovery of Uranium from
Contaminated Subsurface Environments with Electrodes." Environmental Science
& Technology 39(22): 8943-8947.
Hamman, C. H., Hamnett, A. and Vielstich, W. (2007). Electrochemistry, Wiley - VCH.
He, Z. and Angenent, L. T. (2006). "Application of Bacterial Biocathodes in Microbial
Fuel Cells." Electroanalysis 18(19-20): 2009-2015.
He, Z., Huang, Y., Manohar, A. K. and Mansfeld, F. (2008). "Effect of Electrolyte Ph on
the Rate of the Anodic and Cathodic Reactions in an Air-Cathode Microbial Fuel
Cell." Bioelectrochemistry In Press.
He, Z. and Mansfeld, F. (2009). "Exploring the Use of Electrochemical Impedance
Spectroscopy (Eis) in Microbial Fuel Cell Studies." Energy & Environmental
Science 2(2): 215-219.
He, Z., Shao, H. B. and Angenent, L. T. (2007). "Increased Power Production from a
Sediment Microbial Fuel Cell with a Rotating Cathode." Biosensors &
Bioelectronics 22: 3252-3255.
He, Z., Wagner, N., Minteer, S. D. and Angenent, L. T. (2006). "An Upflow Microbial
Fuel Cell with an Interior Cathode: Assessment of the Internal Resistance by
Impedance Spectroscopy." Environmental Science & Technology 40(17): 5212-
5217.
Heitz, E. and Kreysa, G. (1986). Priciples of Electrochemical Engineering, VCH.
Hjelm, A. K. and Lindbergh, G. (2002). "Experimental and Theoretical Analysis of
Limn2o4 Cathodes for Use in Rechargeable Lithium Batteries by Electrochemical
Impedance Spectroscopy (Eis)." Electrochimica Acta 47(11): 1747-1759.

81
Karube, I., Matsunaga, T., Tsuru, S. and Suzuki, S. (1976). "Continous Hydrogen
Production by Immobilized Whole Cells of Clostridium Butyricum." Biochimica
et Biophysica Acta (BBA) - General Subjects 444(2): 338-343.
Kim, B. H., Chang, I. S., Cheol Gil, G., Park, H. S. and Kim, H. J. (2003). "Novel Bod
(Biological Oxygen Demand) Sensor Using Mediator-Less Microbial Fuel Cell."
Biotechnology Letters 25(7): 541.
Kim, B. H., Park, H. S., Kim, H. J., Kim, G. T., Chang, I. S., Lee, J. and Phung, N. T.
(2004). "Enrichment of Microbial Community Generating Electricity Using a
Fuel-Cell-Type Electrochemical Cell." Applied Microbiology and Biotechnology
63(6): 672.
Liu, H., Grot, S. and Logan, B. E. (2005). "Electrochemically Assisted Microbial
Production of Hydrogen from Acetate." Environ. Sci. Technol. 39(11): 4317-4320.
Logan, B. E., Hamelers, B., Rozendal, R., Schroder, U., Keller, J., Freguia, S., Aelterman,
P., Verstraete, W. and Rabaey, K. (2006). "Microbial Fuel Cells: Methodology
and Technology." Environ. Sci. Technol. 40(17): 5181-5192.
Manohar, A. K., He, Z. and Mansfeld, F. (2009). The Use of Electrochemical Impedance
Spectroscopy (EIS) for the Evaluation of the Electrochemical Properties of
Microbial Fuel Cells. Bioelectrochemical Systems from Extracellular Electron
Transfer to Biotechnological Application. K. Rabaey, L. T. Angenent, U.
Schroder and J. Keller, IWA Publishing.
Mansfeld, F. (1990). "Electrochemical Impedance Spectroscopy (Eis) as a New Tool for
Investigating Methods of Corrosion Protection." Electrochimica Acta 35(10):
1533-1544.
Mansfeld, F. (1995). "Use of Electrochemical Impedance Spectroscopy for the Study of
Corrosion Protection by Polymer-Coatings." Journal of Applied Electrochemistry
25(3): 187-202.
Mansfeld, F. (2005). "Tafel Slopes and Corrosion Rates Obtained in the Pre-Tafel Region
of Polarization Curves." Corrosion Science 47(12): 3178-3186.
Mansfeld, F. (2006a). "Classic Paper in Corrosion Science and Engineering with a
Perspective by F. Mansfeld." Corrosion 62(10): 843-844.

82
Mansfeld, F. (2006b). Electrochemical Impedance Spectroscopy. Analytical Methods in
Corrosion Science and Engineering. P. Marcus and F. Mansfeld, CRC Press: 463-
505.
Mansfeld, F. (2007a). An Evaluation of a Microbial Fuel Cell Using Different
Electrochemical Techniques. 7th International Symposium on Electrochemical
Impedance Spectroscopy, June 3 - 8, 2007, Argelès-sur-Mer, France.
Mansfeld, F. (2007b). "The Interaction of Bacteria and Metal Surfaces." Electrochimica
Acta 52(27): 7670-7680.
Mansfeld, F. (2009). "Fundamental Aspects of the Polarization Resistance Technique-the
Early Days." Journal of Solid State Electrochemistry 13(4): 515-520.
Mansfeld, F. and Kendig, M. W. (1985). "Electrochemical Impedance Spectroscopy of
Protective Coatings." Materials and Corrosion/Werkstoffe und Korrosion 36 (11):
473-483
Mansfeld, F., Shih, H., Greene, H. and Tsai, C. H. (1993). ASTM STP 37: 1188.
Mansfeld, F., Tsai, C. H. and Shih, H. (1992). ASTM STP 186: 1154.
Min, B., Kim, J. R., Oh, S. E., Regan, J. M. and Logan, B. E. (2005). "Electricity
Generation from Swine Wastewater Using Microbial Fuel Cells." Water Research
39(20): 4961-4968.
Min, B. and Logan, B. E. (2004). "Continuous Electricity Generation from Domestic
Wastewater and Organic Substrates in a Flat Plate Microbial Fuel Cell."
Environmental Science & Technology 38(21): 5809-5814.
Niessen, J., Schröder, U., Rosenbaum, M. and Scholz, F. (2004). "Fluorinated
Polyanilines as Superior Materials for Electrocatalytic Anodes in Bacterial Fuel
Cells." Electrochemistry Communications 6(6): 571-575.
Oldham, K. B. and Mansfeld, F. (1973). "Corrosion Rates from Polarization Curves -
New Method." Corrosion Science 13(10): 813-819.
Ouitrakul, S., Sriyudthsak, M., Charojrochkul, S. and Kakizono, T. (2007). "Impedance
Analysis of Bio-Fuel Cell Electrodes." Biosensors & Bioelectronics 23(5): 721-
727.

83
Park, D. H., Kim, S. K., Shin, I. H. and Jeong, Y. J. (2000). "Electricity Production in
Biofuel Cell Using Modified Graphite Electrode with Neutral Red."
Biotechnology Letters 22(16): 1301-1304.
Park, D. H. and Zeikus, G. J. (2002). "Impact of Electrode Composition on Electricity
Generation in a Single-Compartment Fuel Cell Using Shewanella Putrefaciens."
Applied Microbiology and Biotechnology 59(1): 58.
Park, D. H. and Zeikus, G. J. (2003). "Improved Fuel Cell and Electrode Designs for
Producing Electricity from Microbial Degradation." Biotechnology and
Bioengineering 81(3): 348-355.
Park, H. S., Kim, B. H., Kim, H. S., Kim, H. J., Kim, G. T., Kim, M., Chang, I. S., Park,
Y. K. and Chang, H. I. (2001). "A Novel Electrochemically Active and Fe(III)-
Reducing Bacterium Phylogenetically Related to Clostridium Butyricum Isolated
from a Microbial Fuel Cell." Anaerobe 7(6): 297.
Pham, C. A., Jung, S. J., Phung, N. T., Lee, J., Chang, I. S., Kim, B. H., Yi, H. and Chun,
J. (2003). "A Novel Electrochemically Active and Fe(Iii)-Reducing Bacterium
Phylogenetically Related to Aeromonas Hydrophila, Isolated from a Microbial
Fuel Cell." FEMS Microbiology Letters 223(1): 129.
Prasad, D., Arun, S., Murugesan, A., Padmanaban, S., Satyanarayanan, R. S., Berchmans,
S. and Yegnaraman, V. (2007). "Direct Electron Transfer with Yeast Cells and
Construction of a Mediatorless Microbial Fuel Cell." Biosensors & Bioelectronics
22(11): 2604-2610.
Qiao, Y., Li, C. M., Bao, S. J. and Bao, Q. L. (2007). "Carbon Nanotube/Polyaniline
Composite as Anode Material for Microbial Fuel Cells." Journal of Power
Sources 170(1): 79-84.
Rabaey, K., Boon, N., Siciliano, S. D., Verhaege, M. and Verstraete, W. (2004). "Biofuel
Cells Select for Microbial Consortia That Self-Mediate Electron Transfer."
Applied and Environmental Microbiology 70(9): 5373-5382.
Ramasamy, R. P., Gadhamshetty, V., Nadeau, L. J. and Johnson, G. R. (2009).
"Impedance Spectroscopy as a Tool for Non-Intrusive Detection of Extracellular
Mediators in Microbial Fuel Cells." Biotechnology and Bioengineering 104(5):
882-891.

84
Ramasamy, R. P., Ren, Z. Y., Mench, M. M. and Regan, J. M. (2008). "Impact of Initial
Biofilm Growth on the Anode Impedance of Microbial Fuel Cells."
Biotechnology and Bioengineering 101(1): 101-108.
Rhoads, A., Beyenal, H. and Lewandowski, Z. (2005). "Microbial Fuel Cell Using
Anaerobic Respiration as an Anodic Reaction and Biomineralized Manganese as a
Cathodic Reactant." Environmental Science & Technology 39(12): 4666-4671.
Shih, H. and Mansfeld, F. (1992). ASTM STP. 1154: 174.
Sibel, D. R., Bennetto, H. P., Gerard, M. D., Jeremy, R. M., John, L. S. and Christopher,
F. T. (1984). "Electron-Transfer Coupling in Microbial Fuel Cells: 1. Comparison
of Redox-Mediator Reduction Rates and Respiratory Rates of Bacteria." Journal
of chemical technology and biotechnology. Biotechnology 34(1): 3-12.
Srikanth, S., Marsili, E., Flickinger, M. C. and Bond, D. R. (2008). "Electrochemical
Characterization of Geobacter Sulfurreducens Cells Immobilized on Graphite
Paper Electrodes." Biotechnology and Bioengineering 99(5): 1065-1073.
Taberna, P. L., Simon, P. and Fauvarque, J. F. (2003). "Electrochemical Characteristics
and Impedance Spectroscopy Studies of Carbon-Carbon Supercapacitors." Journal
of the Electrochemical Society 150(3): A292-A300.
Ter Heijne, A., Hamelers, H. V. M., De Wilde, V., Rozendal, R. A. and Buisman, C. J. N.
(2006). "A Bipolar Membrane Combined with Ferric Iron Reduction as an
Efficient Cathode System in Microbial Fuel Cells." Environmental Science &
Technology 40(17): 5200-5205.
Yokoyama, H., Ohmori, H., Ishida, M., Waki, M. and Tanaka, Y. (2006). "Treatment of
Cow-Waste Slurry by a Microbial Fuel Cell and the Properties of the Treated
Slurry as a Liquid Manure." Animal Science Journal 77(6): 634-638.
You, S., Zhao, Q., Zhang, J., Jiang, J., Wan, C., Du, M. and Zhao, S. (2007). "A
Graphite-Granule Membrane-Less Tubular Air-Cathode Microbial Fuel Cell for
Power Generation under Continuously Operational Conditions." Journal of Power
Sources 173(1): 172-177.
You, S. J., Zhao, Q. L., Zhang, J., Liu, H., Jiang, J. Q. and Zhao, S. Q. (2008). "Increased
Sustainable Electricity Generation in up-Flow Air-Cathode Microbial Fuel Cells."
Biosensors & Bioelectronics 23(7): 1157-1160.

85
You, S. J., Zhao, Q. L., Zhang, J. N., Jiang, J. Q. and Zhao, S. Q. (2006). "A Microbial
Fuel Cell Using Permanganate as the Cathodic Electron Acceptor." Journal of
Power Sources 162(2): 1409-1415.
Zhao, F., Harnisch, F., Schroder, U., Scholz, F., Bogdanoff, P. and Herrmann, I. (2006).
"Challenges and Constraints of Using Oxygen Cathodes in Microbial Fuel Cells."
Environmental Science & Technology 40(17): 5193-5199.
Zhao, F., Harnisch, F., Schröder, U., Scholz, F., Bogdanoff, P. and Herrmann, I. (2005).
"Application of Pyrolysed Iron(Ii) Phthalocyanine and Cotmpp Based Oxygen
Reduction Catalysts as Cathode Materials in Microbial Fuel Cells."
Electrochemistry Communications 7(12): 1405-1410.
Zhao, F., Slade, R. C. T. and Varcoe, J. R. (2009). "Techniques for the Study and
Development of Microbial Fuel Cells: An Electrochemical Perspective."
Chemical Society Reviews 38(7): 1926-1939.

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Chapter 2: Effect of Different Chromium Pretreatments and Primers on
the Corrosion Behavior of Polymer Coated Aluminum 2024

2.1 Introduction

Aluminum and its alloys are widely used in the aerospace industry because of their light
weight, ease of fabrication and relatively high resistance to corrosion (Davis 1999). When
exposed to the atmosphere, an oxide layer is formed on the surface of aluminum which
provides reasonably good corrosion resistance. In order to increase the strength of pure
aluminum, elements such as copper, magnesium, silicon, manganese and zinc are alloyed
to it. However, as a result of this alloying, the corrosion resistance of aluminum decreases
with some alloying elements. Aluminum alloys, when exposed to corrosive media
containing chloride ions experience localized attack known as pitting. In order to protect
aluminum alloys from localized corrosion, different methods are being adopted.
Anodizing of aluminum, the cladding process, applying a chromate conversion coating
and the use of corrosion inhibitors are some of the methods that are used at present to
protect aluminum alloys from corrosion.

Application of chromate conversion coatings (CCC) is one of the most extensively used
methods for corrosion protection of aluminum alloys. CCCs contain chromium in its
hexavalent form (Cr
6+
) and other chemicals such as fluorides and cyanides are also
present in these coatings (Buchheit et al. 1994). Eventhough CCC provide good corrosion

87
resistance for aluminum alloys in most environments, the Cr
6+
ingredient and the
fluorides and cyanides present in the CCCs are toxic and carcinogenic in nature. This has
resulted in several environmental regulations that mandate the elimination of Cr
6+
compounds from use in industries (Zeng et al. 2006).

Several alternatives to using CCCs for protecting aluminum alloys from corrosion have
been proposed (Rangel and Travassos 1992; Buchheit et al. 1994; Wang 1994).
Replacement of Cr
6+
in the coating by trivalent chromium (Cr
3+
) is being studied widely
as a possible method for replacing Cr
6+
(Song and Chin 2002; Yu et al. 2008b) based
coatings.

A major requirement in the discovery of a successful alternative to Cr
6+
coatings is the
proper evaluation of the protective properties of modified coatings. Several
electrochemical and analytical techniques are being used which could provide useful
information about the chemistry of the coating and its interaction with the metal surface.
Electrochemical Impedance Spectroscopy (EIS) is a very powerful technique to study the
properties of protective coatings. EIS is a non-destructive method that allows assessing
corrosion protection by coatings as a function of expensive exposure periods (Mansfeld et
al. 1986; Mansfeld 1994; Mansfeld 1995; Mansfeld et al. 1998).

88
2.2 Literature Review

2.2.1 Corrosion Behavior of Aluminum and its Alloys

Pure aluminum and most aluminum alloys, when exposed to air form a continuous oxide
layer (Al
2
O
3
) which has a thickness of about 10 Å. This oxide layer provides corrosion
resistance in neutral and acid environments but not in alkaline solutions. Alloys in which
copper is the principal constituent fall under the 2xxx series of aluminum alloys (Davis
1999). The most important effect of copper is the increase in the strength-to-weight ratio
of the alloy. Alloying with copper however increases the susceptibility of aluminum to
pitting corrosion. Copper present in the alloy dissolves and then redeposits from solution
resulting in the formation of local galvanic cells on the surface of the alloy. These copper
rich areas act as cathodes on which oxygen and proton reduction takes place at a much
faster rate than the surrounding alloy which becomes the anode (Aziz and Godard 1952).

2.2.2. Corrosion Protection of Al Alloys Using Chromate Conversion Coatings

Conversion coatings refer to coatings in which metal ions from the substrate become part
of the coating (Schweitzer 2006). The conversion layer forms an electrically insulating
barrier layer between the coating and the base metal (Schweitzer 2006) thereby inhibiting
the penetration of corrosive species from the solution that have penetrated the coating
layer above it. The corrosion products of the base metal that are contained in the

89
conversion coating also provide some degree of corrosion protection. Oxides, chromates
and phosphates are some of the conversion coating systems used in corrosion protection.
Chromate conversion coatings are one of the most frequently used methods of corrosion
protection of aluminum alloys (Kendig and Buchheit 2003).

Chromium is used as a corrosion inhibitor for different metals including aluminum, zinc
and steel. Chromate conversion coatings provide adequate corrosion protection for
aluminum alloys and also facilitate better adherence between the aluminum substrate and
the coating layers (Burns and Bradley 1967; Kendig and Buchheit 2003).

The formation of a CCC involves the following oxidation-reduction reactions (Kendig et
al. 2001)

O H OH Cr e H O Cr
2 3
2
7 2
) ( 2 6 8 + ↔ + +
− + −
(1)
− +
+ ↔ e Al Al 3
3
(2)

CCCs are typically about 10-100nm in thickness and consists mainly of trivalent
chromium and hexavalent chromium compounds (Wang 1994).

The CCC baths contain a source of hexavalent chromium ion, an acid to reduce the pH
and a source of fluoride ions. The fluoride ions help removing the natural oxide layer and

90
facilitate the formation of the conversion layer. The fluoride ions attack the aluminum
oxide film to expose the base metal. The conversion coating layer then forms on the bare
metal surface (Kendig et al. 2001). The hexavalent chromium present in the coating is
mobile and helps in the dynamic repair of the coating by a process known as ‘self-
healing’. Self healing is the process by which a hexavalent chromium ion present in the
coating moves to a defective metal site exposed to corrosive media, gets reduced to the
trivalent form and prevents corrosion (Kendig et al. 2001).

This self healing characteristic of CCCs has been published extensively in the literature.
Jun et al have reported a study where two samples of aluminum were placed very close to
each other in corrosive media. One sample was coated with a CCC while the other
sample was bare and uncoated. Using Raman spectroscopy, they have observed the
chromium species leaching into the solution from the sample with the CCC coating and
depositing on the bare sample. They also observed chromium deposits and an increase in
the corrosion resistance of the previously bare sample (Jun et al. 1998).

Kendig et al have summarized the various hypotheses on the mechanism of corrosion
inhibition by CCCs (Kendig and Buchheit 2003). One of these hypothesis is that the
hexavalent chromium ions which are very mobile in solution, get transported to the
regions of corrosion, undergo reduction to form trivalent chromium ions and retard the
oxygen reduction or the hydrogen evolution reaction. Other hypotheses include the
formation of a hydrophobic layer by Cr
3+
ions and modification of the chemical

91
composition of the passive surface oxides on the alloy surface (Kendig and Buchheit
2003).

Aluminum 2024 alloy is rich in copper and is highly susceptible to corrosion. The copper
present in the alloy corrodes from the matrix and redeposits in the metal surface forming
intermetallic areas on the surface of the alloy. Waldrop and Kendig have observed that
the rate of formation of the chromium conversion coatings is faster on Cu-Mn and Cu-Mg
phases than on an Al 2024 alloy which suggests that chromate conversion coatings form
more selectively over areas which act as cathodes on the metal surface and impart
corrosion protection (Waldrop and Kendig 1998).

Even though CCCs have a lot of beneficial effects on aluminum and its alloys from
corrosion, Cr
6+
is highly toxic and carcinogenic. The hazard it poses to the environment
and the operator is very serious and therefore the Environmental Protection Agency (EPA)
and other agencies have proposed very strict regulations on the use and disposal of
hexavalent chromium based compounds (Zeng et al. 2006). This has resulted in the
search for alternatives for CCC that can impart significant protection to aluminum alloys
with minimal or no impact on the environment.

Various alternatives to the CCCs have been proposed in the literature. Mansfeld et al
have developed a process where dipping the aluminum alloy in a CeCl
3
solution provided
corrosion resistant surfaces. The surface of the modified sample did not shown any signs

92
of corrosion after 90 days of exposure to aerated NaCl (Mansfeld et al. 1989). Hinton et
al have studied the effect of different rare earth metal (REM) salts on the corrosion
protection of aluminum alloys (Hinton 1992). Arnott et al have studied the use of REMs
in the preparation of effective conversion coatings on aluminum alloys (Arnott et al.
1989). They treated aluminum alloys in chlorides of cerium, lanthanum and yttrium and
observed that the corrosion resistance of the substrate was much higher with the
transition metal addition than the resistance provided by the natural oxide layer of
aluminum. They reported that when treating with chlorides of cerium, yttrium,
promethium and nickel, the metal ions incorporated into the protective oxide layer of
aluminum which resulted in a decrease of the rate of the oxidation reduction reaction on
the alloy (Arnott et al. 1989).

Mansfeld et al have developed a process involving the immersion of aluminum alloy in
hot solutions of cerium nitrate and cerium chloride (Mansfeld et al. 1992b) followed by
polarizing the sample at (0.5V vs SCE) in a deareated molybdate solution. This treatment
results in a protective surface layer that contains both cerium and molybdenum and
prevents localized corrosion (Mansfeld et al. 1992b).

Xingwen et al (Xingwen et al. 2001) have introduced the use of a double layer REM
coating on aluminum alloys where they used borate and carbonate salts of cerium in the
pretreatment process. Using EIS, they observed that the treatment increased the corrosion
resistance of the aluminum alloy surface (Xingwen et al. 2001).

93
2.2.3 Trivalent Chromium Pretreatment (TCP)

One of the most extensively studied alternatives for the replacement of hexavalent
chromium based CCCs is the trivalent chromium pretreatment method. Trivalent
chromium is relatively harmless for the environment when compared to the hexavelent
form and the electrochemical equivalent weight of trivalent chromium is twice that of the
hexavelent form (Song and Chin 2002). Trivalent chromium bath formulations typically
consist of chromium chloride or chromium sulphate where chromium is present in its
trivalent form, complexing agents, buffer and brighteners (Song and Chin 2002).

Yu et al have studied the corrosion resistance of trivalent chromium treated aluminum
6063 alloy exposed to 3.5 wt% NaCl using polarization curves and EIS (Yu et al. 2008b).
They have observed that the corrosion resistance of the alloy after the treatment with
trivalent chromium had increased markedly compared to that of the untreated alloy. They
stated that Cr
3+
inhibits corrosion by decreasing the rate of both the anodic and cathodic
partial reactions and therefore acts as a mixed type of corrosion inhibitor (Yu et al.
2008b). The authors have performed SEM imaging and ECS and XPS analysis which
revealed the presence of a trivalent chromium film (Yu et al. 2008b).

Yu et al have studied the influence of the addition of urea and thiourea on the corrosion
inhibition provided by trivalent chromium coatings (Yu et al. 2008a). Using polarization
curves and impedance measurements, they have observed an increase in the corrosion

94
protection by trivalent chromium coatings after the addition of urea and thiourea (Yu et al.
2008a).

Trivalent chromium being a mild oxidizer, does not cause as much harm to human beings
as hexavelent chromium but under certain conditions, compounds containing Cr
3+
could
oxidize to Cr
6+
form (Apte et al. 2006; Berger et al. 2007).

2.3 Experimental Approach
2.3.1 Sample Preparation

The samples investigated in this study were prepared at the NAVAIR facility at Pax
River and provided to the USC investigators by Dr. Peter Zarras at NAVAIR, China Lake,
CA (Zarras 2010). Two sets of samples, one with a pretreatment layer, primer and
topcoat, and another set with a pretreatment and primer coat but without topcoat were
evaluated. The pretreatment layer was applied by a spray application and the primer and
topcoat were applied using HVLP (high volume, low pressure) spray equipment (Zarras
2010). The matrix for the various coating formulations tested in this study is shown in
Table 2.1 (Zarras 2010). Three samples were provided in each type of coating
formulation.

95
Table 2. 1: Formulation of the coatings tested
Sample # Pretreatment Primer Topcoat
27-29
chromated
pretreatment
chromated epoxy
primer
polyurethane
topcoat (non-
chromate)
30-32
chromated
pretreatment
non-chromated
epoxy primer
polyurethane
topcoat (non-
chromate)
46-48
TCP
pretreatment
non-chromated
epoxy primer
polyurethane
topcoat (non-
chromate)
1-3
chromated
pretreatment
chromated epoxy
primer
-
4-6
TCP
pretreatment
non-chromated
epoxy primer
-

Samples 27-29 had a chromate conversion coating pretreatment, a chromate based epoxy
primer and a non-chromate based polyurethane top coat. Samples 30-32 had a chromate
conversion coating pretreatment and a polyurethane top coat similar to the samples 27-29
but a non-chromate based epoxy primer. Samples 46-49 had a trivalent chromium
pretreatment, a non-chromate based epoxy primer and a polyurethane based top coat.
Samples 1-3 had a chromate conversion coating pretreatment, a chromate based epoxy
primer whereas samples 4-6 had a trivalent chromium pretreatment and a non-chromate
based epoxy primer. For all samples, the thickness of the pretreatment layer was about
0.1 μm, the thickness of the primer and top coat layers were about 0.9 mil and 1.5 to 2
mils respectively. The total thickness of the coating layer on these sample was about 2.5

96
to 3.0 mils (Zarras 2010).

The chromate conversion coatings (CCC) on samples 27-29 and 1-3 were prepared using
the commericially available Alodine® 1200S system which is used on aluminum surfaces
to increase their resistance to corrosion and improve adhesion between the base metal and
the paint layer (Henkel International). The trivalent chromium treatments (TCP) were
prepared using the commercially available SurTec® 650 chromitAl® TCP system
(SurTec International). This system is free of the environmentally toxic and carcinogenic
hexavelent chromium in its composition.

The primers and the topcoats that were used for the various coating systems were
obtained from Deft Inc (Zarras 2010). The chromate based epoxy primer is highly
resistant to chemicals and corrosion, and maintains good adhesion with the substrate
(Deft Inc). They also provide a suitable layer for applying the topcoat (Deft Inc). The
non-chromated epoxy primer is an epoxy-polyamide based primer. The topcoat used for
samples 27-29, 30-32 and 46-48 are polyurethane based topcoats commercially available
from Deft Inc (Deft Inc).

2.3.2 Experimental Methods

An electrochemical cell specifically developed for testing of coatings at CEEL, USC was
used in this study. Using this cell, a fixed area of the sample could be exposed to the

97
corrosive medium. The exposed area of the sample was 3.97cm
2
. A saturated calomel
electrode (SCE) and a stainless steel 316 sheet were used as the reference and the counter
electrode, respectively.

Electrochemical Impedance Spectroscopy:

The samples were exposed to 0.5N NaCl open to air at room temperature and the
impedance spectra were measured periodically for a period of 31 days. Measurements
were made with a Gamry PCI4 and Gamry Reference 600 potentiostats using the EIS 300
software. The impedance spectra were measured at the open-circuit potential (E
corr
) of the
samples in a frequency range of 100kHz to 1mHz. The magnitude of the applied AC
signal was 10mV. The measured impedance spectra were analyzed using the COATFIT
module of the ANALEIS software (Mansfeld et al. 1992a; Mansfeld et al. 1993;
Mansfeld 2006).

2.4 Results and Discussion
2.4.1 Samples with Pretreatment, Primer and Topcoat

The impedance spectra for all samples were measured periodically for a total duration of
31 days. Three samples were tested for each different coating system to be studied. All
samples were exposed to 0.5N NaCl open to air. The impedance spectra of sample 28
measured over the entire exposure period are shown in Fig. 2.1 as representative of the

98
set 27-29 (Table 2.1). The impedance spectra are presented as Bode-plots, where the
logarithm of the frequency f is plotted against the logarithm of the impedance modulus
|Z| and the phase angle.

-3 -2 -1 0 1 2 3 4 5
3
4
5
6
7
8
9
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
#28
1d. Ecorr = -0.390V
7d. Ecorr = -0.168V
14d. Ecorr = -0.336V
21d. Ecorr = -0.463V
31d. Ecorr = -0.438V

Fig. 2.1: Impedance spectra for sample # 28 at different exposure times.

As noted in Table 2.1, samples 27-28 have a chromate based pretreatment with a

99
chromate primer and polyurethane based topcoat. The impedance spectra of sample 28
did not show any significant changes during the 31 day exposure period and the coating
appears to be very stable and protective.

A small region where the data appears to be scattered is observed in the mid frequency
region. The frequency at which is observed is close to 60Hz which is the frequency of the
domestic power supply. It is suspected that ambient lighting in the laboratory operating
with AC current with at 60Hz might interfere with measurements made around 60Hz.

The impedance spectra of sample 28 follow the one-time-constant model (OTCM) shown
in Fig. 2.2, where the solution resistance, R
s
is in series with a parallel combination of the
pore resistance R
po
and the coating capacitance C
c
(Mansfeld 2006). R
po
represents the
resistance of the electrolyte present in the conductive paths in the coating that reach the
metal surface.

Fig. 2.2: One-time-constant model (OTCM) corresponding to the impedance spectra
shown in Fig. 2.1

The impedance spectra of samples 30 and 46 measured over the 31 day exposure period
are shown in Fig. 2.3 and 2.4, respectively.
c
o
c
o

100

-3 -2 -1 0 1 2 3 4 5
3
4
5
6
7
8
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
#30
1d. Ecorr = -0.561V
7d. Ecorr = -0.679V
14d. Ecorr = -0.679V
21d. Ecorr = -0.693V
31d. Ecorr = -0.650V

Fig. 2.3: Impedance spectra for sample # 30 at different exposure times.

101
-3 -2 -1 0 1 2 3 4 5
3
4
5
6
7
8
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
#46
1d. Ecorr = -0.493V
7d. Ecorr = -0.866V
14d. Ecorr = -0.789V
21d. Ecorr = -0.682V
31d. Ecorr = -0.585V

Fig. 2.4: Impedance spectra for sample # 46 at different exposure times.

Samples 30-32 have a chromated pretreatment, a nonchromated epoxy primer and a non-
chromate polyurethane based topcoat. Sample 46-48 have the same primer and topcoat as

102
samples 30-32, but have a trivalent chromium (TCP) pretreatment (Table 2.1). A
significant difference between the impedance spectra of these two sets of samples and the
first set of samples (27-28) was observed. A second time constant appeared in the low-
frequency region of the impedance spectra for samples 30-32 and 46-48. The second time
constant arises due to the onset of corrosion of the underlying aluminum surface as a
result of attack by the electrolyte which forms conducting paths through pores in the
coatings and reaches the metal surface.

The impedance spectra of these samples can be fitted to the coating model shown in Fig.
2.5 (Mansfeld 1995) which is generally used as the equivalent circuit to describe the
interaction of a polymer coated metal and a corrosive medium. The coating model
consists of the solution resistance R
s
, the coating capacitance C
c
, the pore resistance R
po
,
the polarization resistance and the double layer capacitance C
dl
. The polarization
resistance and the double layer capacitance represent the area of the underlying metal at
which corrosion takes place due to the pores in the coating layer.

Fig. 2.5: Equivalent circuit for the coating model

103
A theoretical Bode plot corresponding to the coating model (Fig. 2.5) for an intact, pore
free coating and a deteriorated coating is shown in Fig. 2.6 (from (Mansfeld 2006)).

Fig. 2.6: Comparison of the impedance spectra of a polymer coated metal with an intact
coating (curve 1) and a deteriorated coating (curve 2) (From (Mansfeld 2006))

Analysis of corrosion protection by different coating systems:
The impedance spectra of samples representing the three different types of coating
systems are shown in Fig. 2.7 a-c for 1 day, 14 days and 31 days of exposure,
respectively. The impedance of the samples 30 and 46 was much lower than that of the
samples 28 during the entire 31 day test period and showed two time constants.

104
-3 -2 -1 0 1 2 3 4 5
3
4
5
6
7
8
9
1 Day
# 28. Ecorr = -0.390V
#30. Ecorr = -0.561V
#46. Ecorr = -0.493V
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
-3 -2 -1 0 1 2 3 4 5
3
4
5
6
7
8
9
14 Day
#28. Ecorr = -0.471V
#30. Ecorr = -0.679V
#46. Ecorr = -0.789V
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
-3 -2 -1 0 1 2 3 4 5
3
4
5
6
7
8
9
31 Day
#28. Ecorr = -0.438V
#30. Ecorr = -0.650V
#46. Ecorr = -0.585V
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0

Fig. 2.7: Comparison of the impedance spectra of samples # 28, 30 and 46 after 1 (a), 14
(b) and 31 (c) days of exposure.
a) b)
c)

105
The impedance spectra for samples 28 and 30, which have the same type of pretreatment,
but different primers, were very different. However, the impedance spectra for samples
30 and 46, which had the same primer, but different pretreatments were quite similar.
These results indicate that the corrosion protection provided by the coating system is
mainly dependent on the type of primer used in the coating.

The absence of a second time constant in the impedance spectra of sample 28 (Fig. 2.1)
indicates that the electrolyte did not attack the base metal through the pores in the coating
layer. For samples 30 and 46, a second time constant was observed in the impedance
spectra indicating porosity of the coating and onset of corrosion of the underlying
aluminum alloy.

The impedance spectra shown in Fig. 2.7 a-c were analyzed using the COATFIT module
of the ANALEIS software developed by Shih and Mansfeld (Mansfeld et al. 1992a;
Mansfeld et al. 1993; Mansfeld 2006) which is based on the equivalent circuit shown in
Fig. 2.5.

The time dependence of the corrosion potential, E
corr
of samples 28, 30 and 46 during
exposure to 0.5N NaCl is shown in Fig. 2.8. Sample 28 had a slightly more noble E
corr

when compared to samples 32 and 46 which had values close to E
corr
of the aluminum
2024 base metal. E
corr
of sample 28 and 32 seems to be very stable over the entire
exposure period, while E
corr
of sample 46 decreased to about -0.890V after 10 days of

106
exposure and then increased to about -0.585V at the end of the 31 day period.
-1
-0.8
-0.6
-0.4
-0.2
0
0 100 200 300 400 500 600 700 800
Time (hrs)
Ecorr (V)
28
30
46

Fig. 2.8: Time dependence of E
corr
of samples # 28, 30 and 46 during exposure to 0.5N
NaCl.

Fig. 2.9 shows the time dependence of C
c
of samples 28, 30 and 46 during the 31 day
exposure period. The capacitance of the coating C
c
is given by:

d
A
Cc
ε ε
0
= , (3)
where ε
0
is the permittivity of free space (8.854 X 10
-14
F/cm), ε is the dielectric constant
of the polymer used in the coating, d is the thickness of the coating and A is the total
exposed area.

107
1.00E-10
1.00E-08
1.00E-06
0 100 200 300 400 500 600 700 800
Time (hrs)
Log Cc (F)
30
46
28
-10
-8
-6

Fig. 2.9: Time dependence of C
c
of samples # 28, 30 and 46 during exposure to 0.5N
NaCl.

C
c
of sample 28 was much lower than C
c
for samples 30 and 46 which were very similar.
C
c
is a function of the dielectric constant of the coating, the exposed surface area and the
thickness of the coating (Eq.3). Since the coating thickness and the surface area were the
same for all the three types of coating samples, the high value of C
c
of samples 30 and 46
may be due to a higher water uptake of these coatings which results in an increase of the
dielectric constant of the coating.

The time dependence of R
po
of the three coating systems is shown in Fig. 2.10. Sample
28 had a much higher value of R
po
compared to samples 30 and 46 which had similar
values of R
po
. Lower values of R
po
indicate that the pores in the coating are filled by the
electrolyte and conducting paths that reach the underlying metal surface are actively

108
being formed. It can be understood from Fig. 2.10 that samples 30 and 46 had a more
porous coating than samples 28.
1000
1E+07
1E+11
0 100 200 300 400 500 600 700 800
Time (hours)
Log Rpo (Ohm)
30
46
28
3
7
11

Fig. 2.10: Time dependence of R
po
of samples # 28, 30 and 46 during exposure to 0.5N
NaCl

The time dependence of the fit parameters C
dl
and R
p
is shown in the Fig. 2.11 and 2.12
respectively. It is observed that samples 30 and 46 have similar values of C
dl
and R
p

respectively.

109
1.00E-05
4.00E-05
7.00E-05
1.00E-04
0 100 200 300 400 500 600 700 800
Time (hrs)
Cdl (F)
30
46

Fig. 2.11: Time dependence of C
d
of samples # 28, 30 and 46 during exposure to 0.5N
NaCl
0.00E+00
7.00E+06
1.40E+07
2.10E+07
2.80E+07
3.50E+07
0 100 200 300 400 500 600 700 800
Time (hrs)
Rp (Ohm)
30
46

Fig. 2.12: Time dependence of R
p
of samples # 28, 30 and 46 during exposure to 0.5N
NaCl.

The double layer capacitance of the sample (Fig. 2.11) can be used to obtain an estimate
the corroding area A
corr
of the underlying alloy. From the value of C
dl
obtained from the
fitting of impedance data, A
corr
can be determined :

110

o
dl
dl
corr
C
C
A = (4)

where C
dl
o
can be assumed as 20μF/cm
2
which has been found to represent C
dl
of iron
alloys exposed to NaCl solution (Titz et al. 1990). This assumption has also been used
frequently in the study of aluminum alloys (Tsai 1992; Kus 2006). Using this value of
A
corr
, the delamination ratio D can be calculated as

A C
C
A
A
D
dl
o
dl corr
.
= = (5)

where A is the total exposed area of the sample.

The delamination ratios D calculated using Eq. 5 for samples 30 and 46 are shown in Fig.
2.13 as a function of exposure time. The values of D were found to be quite low (between
0.003% and 0.012%) and they did not change significantly for both samples during the 31
day exposure period. This result indicates that significant delamination of the coating did
not occur during exposure and new pores or conductive paths were not on the metal
formed in the coating during exposure.

111
0
0.003
0.006
0.009
0.012
0.015
0 100 200 300 400 500 600 700 800
Time (days)
D
30
46

Fig. 2.13: Time dependence of D of samples # 28, 30 and 46 during exposure to 0.5N
NaCl.

2.4.2 Analysis of Impedance Spectra of Scribed Samples (With Topcoat):

After 31 days of exposure, one sample from every coating system was scribed. Scribing
was performed using a hand held scribing tool and an “X” was made on the sample. This
was done by scribing two lines along the diagonals of the square shaped samples. The
scribed samples were then exposed to 0.5N NaCl for a period of 3 days. The impedance
spectra of the samples were measured daily during this period.

The impedance spectra of scribed sample 28 and 30 are shown in Fig. 2.14 and 2.15
respectively. The E
corr
values of the scribed samples determined on day 1 after scribing
are shown in Table 2.2 follow the same pattern as E
corr
for the unscribed samples. E
corr
of

112
sample 28 was less negative than E
corr
of samples 30 and 46 and sample 46 had E
corr

values closer or more negative than E
corr
of Al 2024.
-3 -2 -1 0 1 2 3 4 5
2
3
4
5
6
7
8
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
28
3hr. Ecorr = -0.723V
1d. Ecorr = -0.558V

Fig. 2.14: Impedance spectra for scribed sample # 28 at different exposure times.

113
Table 2. 2: E
corr
of scribed samples after 1 day of exposure
Sample # 28 30 46
E
corr
(V) -0.558 -0.645 -0.709

-3 -2 -1 0 1 2 3 4 5
1
2
3
4
5
6
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
30
2d. Ecorr = -0.676V
3d. Ecorr = -0.678V

Fig. 2.15 : Impedance spectra for scribed sample # 30 at different exposure times.

114
The impedance spectra of the scribed sample 46 shown in Fig. 2.16 and it corresponds to
a three time constant model. Pitting of the underlying aluminum alloy could be
contributing to the additional time constants observed for this sample.
-3 -2 -1 0 1 2 3 4 5
2
3
4
5
6
7
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
46
1d. Ecorr = -0.741V
2d. Ecorr = -0.709V

Fig. 2.16: Impedance spectra for scribed sample # 30 at different exposure times.

115
The impedance spectra of the three scribed samples (Fig. 2.14-2.16) suggest that samples
28 and 30 did not undergo rapid corrosion of the substrate whereas sample 46 exhibited
signs of pitting processes happening at the bare aluminum surface. Samples 28 and 30
have a chromate pretreatment which might be responsible for their corrosion resistance
even in the scribed condition. Chromate conversion coatings have a “self healing”
charecteristic whereby when the coating in a particular region is damaged, chromium
ions from the surrounding coating migrate to the damaged surface and act as inhibitors
protecting the metal from corrosion in the scribed region.

Optical Evaluations of scribed samples
Observation of scribed sample 28 after 3 days of exposure to 0.5N NaCl under an optical
microscope (Fig. 2.17) did not reveal any significant delamination of the coating or the
presence of corrosion products in the area where the two scribes meet.

116

Fig. 2.17: Optical micrograph of scribed sample # 28 after 3 days of exposure to 0.5N
NaCl.

At the intersection of the two scribe lines on the sample the coating seems to be well
adherent to the substrate metal and no corrosion products are seen.

Fig. 2.18 shows the image for scribed sample 30 for which corrosion of the substrate had
occurred in the scribe lines. Near the area where the two lines of the scribe intersect,
corrosion products can be observed.

117

Fig. 2.18: Optical micrograph of scribed sample # 30 after 3 days of exposure to 0.5N
NaCl.

Fig. 2.19: Optical micrograph of scribed sample # 46 after 3 days of exposure to 0.5N
NaCl.

118
Fig. 2.19 shows an optical micrograph of scribed sample 46 after 3 days of exposure.
Some corrosion products are seen and upon closer examination, in the area surrounding
the scribe, undercutting and lifting off of the coating could be observed.

2.4.3 Samples with Pretreatment and Primer, but without Top Coat

Two sets of sample which had different types of pretreatment and primer layers, but no
top coat on Al 2024 alloy were also investigated. Samples 1-3 had a chromate conversion
coating with a chromated epoxy based primer and samples 4-6 were treated with trivalent
chromium (TCP) and covered with a non-chromate epoxy based primer (Table 2.1). The
impedance spectra of the six samples were measured periodically for a period of 31 days.

The results of samples 3 and sample 4 will be discussed here as the representative from
their respective sets of samples. The impedance spectra of sample 3 are shown in Fig.
2.20 for different exposure times.

119
-3 -2 -1 0 1 2 3 4 5
3
4
5
6
7
8
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
3
1d. Ecorr = -0.405V
7d. Ecorr = -0.391V
14d. Ecorr = -0.373V
21d. Ecorr = -0.355V
31d. Ecorr = -0.339V

Fig. 2.20: Impedance spectra of sample # 3 for different exposure times

The impedance spectra followed a OTCM for the first 14 days of exposure, but a second
time constant appeared in the very low frequency region of the impedance spectra for
longer exposure times as indicated by the frequency dependence of the phase angle. The
impedance spectra changed slightly with time indicating that the protective properties of

120
the coating decreased during longer exposure periods to 0.5N NaCl.

Significant changes were observed in the impedance spectra of sample 4 during the entire
exposure period (Fig. 2.21). The high-frequency region shows an increase of C
c
with
exposure time, which is probably due to the water uptake by the coating.
-3 -2 -1 0 1 2 3 4 5
2
3
4
5
6
7
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
4
1d. Ecorr = -0.620V
7d. Ecorr = -0.429V
14d. Ecorr = -0.926V
21d. Ecorr = -0.766V
31d. Ecorr = -0.517V

Fig. 2.21: Impedance spectra of sample # 4 for different exposure times

121
-3 -2 -1 0 1 2 3 4 5
3
4
5
6
7
8
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
1d
# 3. Ecorr = -0.405V
# 4. Ecorr = -0.620V
-3 -2 -1 0 1 2 3 4 5
2
3
4
5
6
7
8
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
14d
# 3. Ecorr = -0.311V
# 4. Ecorr = -0.926V
-3 -2 -1 0 1 2 3 4 5
2
3
4
5
6
7
8
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
21d
# 3. Ecorr = -0.284V
# 4. Ecorr = -0.517V

Fig. 2.22: Comparison of impedance spectra of samples # 3 and 4 for (a) 1, (b) 14 and (c)
31 days of exposure.
a) b)
c)

122
The low-frequency region of the impedance spectra showed significant changes of C
dl

and R
p
.

A comparison of the impedance spectra of samples 3 and 4 at different times during the
31 day test period shows that the impedance of sample 4 was always much lower than the
impedance of the sample 3 (Fig 2.22). From the high-frequency region of the impedance
spectra it could be qualitatively inferred that C
c
of sample 4 is higher than C
c
of sample 3
which could be due to increased water uptake of the coating. Similar behavior was also
observed with the non chromate primer coatings (30 and 46) (Fig 2.7).

The impedance spectra shown in Fig. 2.22 were fitted to the coating model shown in Fig.
2.5 using the COATFIT module of the ANALEIS software.

-1
-0.8
-0.6
-0.4
-0.2
0
0 100 200 300 400 500 600 700 800
Time (hours)
Ecorr (V)
3
4
`

Fig. 2.23: Time dependence of E
corr
of samples # 3 and 4 during exposure to 0.5N NaCl.

123
E
corr
of the sample 3 was less negative than E
corr
of sample 4 (Fig. 2.23). E
corr
of sample 4
decreased initially for about 10 days to about -0.9V and after that increased to about -
0.58V. These results are similar to the behavior of sample 28 and 46 in Fig. 2.8 which
have the same pretreatment and primer as sample 3 and 4, respectively.

C
c
of sample 4 was higher than C
c
of sample 3 as observed from the impedance spectra
(Fig. 2.24) of these samples. C
c
of the two samples did not change significantly during
the 31 day exposure period which suggests that significant water uptake by these coatings
did not occur during exposure.

0.00E+00
1.00E-08
2.00E-08
3.00E-08
4.00E-08
5.00E-08
0 100 200 300 400 500 600 700 800
Time (hours)
Cc (F)
3
4
`

Fig. 2.24: Time dependence of C
c
of samples # 3 and 4 during exposure to 0.5N NaCl.

The time dependence of R
po
of the two samples is shown in Fig. 2.25. R
po
of sample 3
was much higher and decreased with time, while R
po
of sample 4 decreased much rapidly

124
with time indicating a rapidly deteriorating coating as can also be qualitatively observed
in the mid frequency region of the impedance spectra shown in Fig. 2.22 The increase in
C
c
and the simultaneous decrease in R
po
of sample 4 suggest that conductive paths are
continuously being formed in the coating layer.
1.00E+04
1.00E+07
1.00E+10
0 100 200 300 400 500 600 700 800
Time (Hours)
Log Rpo (Ohm)
3
4
4
7
10

Fig. 2.25: Time dependence of R
po
of samples # 3 and 4 during exposure to 0.5N NaCl.

The time dependence of C
dl
shown in Fig. 2.26a indicates that the area of active metal
corrosion was very small for sample 3. This is further validated by the very high R
p

values for sample 3 as shown in Fig. 2.26b.

The comparison of the fit parameters suggests that the sample with the chromate
conversion coating and chromate containing epoxy based primer provided better
corrosion protection for the samples without the top coat.

125
1.00E-06
1.00E-05
1.00E-04
0 100 200 300 400 500 600 700 800
Time (hours)
Log Cd (F)
3
4
`
a)
-6
-5
-4
0.00E+00
2.00E+07
4.00E+07
6.00E+07
0 100 200 300 400 500 600 700 800
Time (hours)
Rp (Ohm)
3
4
b)

Fig. 2.26: Time dependence of C
dl
(a) and R
p
(b) of samples # 3 and 4 during exposure to
0.5N NaCl.

The delamination ratio of the sample 3 calculated using Eq. 5 shown in Fig. 2.27 was
very low and did not increase with exposure time. For sample 4 with the TCP
pretreatment and the non-chromate based primer, D increased significantly as a function
of time which is due to the formation of new pores on the coating layer and also due to
the increase in the volume of the existing pores in the coating resulting in an increase in
the total corroding area of the underlying metal surface.

126
0
0.002
0.004
0.006
0.008
0.01
0.012
0 100 200 300 400 500 600 700 800
Time (hours)
D (%)
3
4

Fig. 2.27: Time dependence of D of samples # 3 and 4 during exposure to 0.5N NaCl

The break point frequency has been suggested to be a useful qualitative indicator for
coating delamination and metal corrosion (Mansfeld et al. 1986; Mansfeld and Tsai 1991;
Mansfeld 1995). The break point frequency, f
b
is related to the coating parameters as
follows

po c
b
R C
f
π 2
1
= (6)

where C
c
and R
po
are the coating capacitance and the pore resistance obtained from the
fitting of the impedance spectra. It can be determined directly from the impedance spectra
as the frequency at which the phase angle equals -45
o
in the high-frequency region
(Mansfeld 2006).

127

The rapid deterioration of the coating in sample 4 as indicated already by the fit
parameter R
po
and D, can be qualitatively identified using f
b
as shown in Fig. 2.28.
0.00E+00
1.00E+02
2.00E+02
3.00E+02
4.00E+02
0 100 200 300 400 500 600 700 800
Time (hours)
fb (Hz)
3
4

Fig. 2.28: Time dependence of f
b
of samples # and 3 and 4

It is observed that f
b
increased significantly with time and using the expression for f
b

above, one can qualitatively estimate that R
po
of the sample is decreasing rapidly with
time indicating the corrosion of the base metal through the pores in the coating layer.

2.4.4 Analysis of Impedance Spectra of Scribed Samples (Without Topcoat).

The impedance spectra of the scribed samples 3 and 4 are shown in Fig. 2.29 a and b,
respectively. Sample 3 which had a chromate conversion coating and a chromate based
primer had impedance spectra corresponding to a OTCM, whereas a second time constant
was observed in the low-frequency region of the impedance spectra for the trivalent

128
chromate pretreated sample (sample 4). Upon scribing the samples, the primer layer was
apparently removed from the scribed area and the bare metal was exposed to the
corrosive medium. In the case of the chromate conversion coated sample, the chromate
conversion layer is “self healing” and inhibits the corrosion of the exposed metal in the
scribe. The second time constant in the impedance spectra corresponding to the scribed
sample 4 could be due to the pitting of aluminum. In the case of TCP pretreated sample,
the protective layer did not form in the scribe area upon exposure to the corrosive
medium and pitting of aluminum initiated.
-3 -2 -1 0 1 2 3 4 5
1
2
3
4
5
6
7
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
3
1d. Ecorr = -0.672V
2d. Ecorr = -0.662V
3d. Ecorr = -0.664V

-3 -2 -1 0 1 2 3 4 5
1
2
3
4
5
6
-3 -2 -1 0 1 2 3 4 5
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
4
1d. Ecorr = -0.623V
2d. Ecorr = -0.643V
3d. Ecorr = -0.650V
Fig. 2.29: Impedance spectra of scribed samples # 3 (a) and # 4 (b).
a) b)

129

Fig. 2. 30: Optical micrograph of scribed sample # 3 after 3 days of exposure

Fig. 2. 31: Optical micrograph of scribed sample # 4 after 3 days of exposure

130
The optical images of the scribed samples 3 and 4 after 3 days of exposure to 0.5N NaCl
are shown in Fig. 2.30 and 2.31, respectively. A shiny uncorroded aluminum surface can
be observed for sample 3, whereas for sample 4, debris of the primer layer and corrosion
products were observed. The aluminum surface that is visible in the scribed region in
sample 4 appears to be pitted. Some delamination of the coating in the area surrounding
the scribe could also be observed for sample 4 (Fig 2.31).

2.5 Conclusions

EIS has been used to evaluate the effects of different pretreatment and primer coats on
corrosion protection of Al 2024. One set of samples with different pretreatment and
primer layers, but with the same topcoat and another set of samples with different
pretreatment and primer coats but without any topcoat were exposed to 0.5N NaCl for a
period of 31 days and their corrosion behavior was studied using EIS.

For the samples with the pretreatment, primer and top coat (27-29, 20-32 and 46-48), the
analysis of the impedance spectra suggests that the sample with the hexavalent chromium
based primer and hexavalent pretreatment provided better corrosion protection for Al
2024 alloy compared to the other systems with the trivalent chromium pretreatment and a
non-chromate primer. The impedance of these samples did not change with time
indicating that the coating was stable and provided adequate corrosion protection of the

131
underlying metal surface. Analysis of the impedance spectra of the scribed samples
demonstrated the “self-healing” characteristic of hexavalent chromate primer. After
scribing the sample, the chromate ions from the areas surrounding the scribe migrated to
the scribed area and protected the bare aluminum surface. This effect was not observed
for the scribed samples with the trivalent chromium pretreatment where the electrolyte
attacked the aluminum substrate and resulted in pitting of the alloy.

Analysis of the impedance spectra of the samples with different pretreatments and primer,
but without a topcoat (1-3 and 4-6) has also been performed. The overall corrosion
resistance of these samples was less than that of the samples with the top coat (27-29, 20-
32 and 46-48) which could be attributed to the decrease of the total thickness of the
coating and the lack of top coat which acts as a barrier. Unlike for the sample with a
topcoat, the impedance spectra of these samples changed with time. The sample with the
chromate conversion pretreatment and a chromate based primer was found to impart
better corrosion protection to the aluminum alloy. The time-dependence of the break-
point frequency f
b
and the delamination ratio D for sample # 4 indicated that the coating
deteriorated significantly during the entire exposure period. Upon scribing sample # 3,
the chromate pretreatment layer self-healed and protected the substrate from corrosion,
whereas significant corrosion of the substrate occurred in sample 4.

132
2.6. Suggestions for Future Work

This study provides a basis for the development of better pretreatment procedures and
primers free of Cr
6+
for corrosion protection of Al 2024. Electrochemical Impedance
Spectroscopy can be used as a non-destructive tool to characterize the properties of a
coating system as a function of exposure time.

133
2.7 Chapter 2 References

Apte, A. D., Tare, V. and Bose, P. (2006). "Extent of Oxidation of Cr(III) to Cr(VI) under
Various Conditions Pertaining to Natural Environment." Journal of Hazardous
Materials 128(2-3): 164-174.
Arnott, D. R., Hinton, B. R. W. and Ryan, N. E. (1989). "Cationic-Film-Forming
Inhibitors for the Protection of the Aa-7075 Aluminum-Alloy against Corrosion in
Aqueous Chloride Solution." Corrosion 45(1): 12-18.
Aziz, P. M. and Godard, H. P. (1952). "Pitting Corrosion Characteristics of Aluminum -
Influence of Magnesium and Manganese." Industrial & Engineering Chemistry
44(8): 1791-1795.
Berger, R., Bexell, U., Grehk, T. M. and Hornstrom, S. E. (2007). "A Comparative Study
of the Corrosion Protective Properties of Chromium and Chromium Free
Passivation Methods." Surface & Coatings Technology 202: 391-397.
Buchheit, R. G., Bode, M. D. and Stoner, G. E. (1994). "Corrosion-Resistant, Chromate-
Free Talc Coatings for Aluminum." Corrosion 50(3): 205-214.
Burns, R. M. and Bradley, W. W. (1967). Protective Coatings for Metals, Reinhold
Publishing Corporation.
Davis, J. R. (1999). Corrosion of Aluminum and Aluminum Alloys, ASM International.
Deft Inc. "Product Information Data Sheet.".
Henkel International. "Technical Data Sheet.".
Hinton, B. R. W. (1992). "Corrosion Inhibition with Rare-Earth-Metal Salts." Journal of
Alloys and Compounds 180: 15-25.
Jun, Z., Gerald, F. and Richard, L. M. (1998). "Corrosion Protection of Untreated Al-
2024-T3 in Chloride Solution by a Chromate Conversion Coating Monitored with
Raman Spectroscopy." Journal of The Electrochemical Society 145(7): 2258-2264.

134
Kendig, M., Jeanjaquet, S., Addison, R. and Waldrop, J. (2001). "Role of Hexavalent
Chromium in the Inhibition of Corrosion of Aluminum Alloys." Surface and
Coatings Technology 140(1): 58-66.
Kendig, M. W. and Buchheit, R. G. (2003). "Corrosion Inhibition of Aluminum and
Aluminum Alloys by Soluble Chromates, Chromate Coatings, and Chromate-Free
Coatings." Corrosion 59(5): 379-400.
Kus, E. (2006). An Electrochemical Evaluation of New Materials and Methods for
Corrosion Protection, University of Southern California. PhD.
Mansfeld, F. (1994). "Determination of the Reactive Area of Organic Coated Metals -
Physical Meaning and Limits of the Break-Point Method - Discussion."
Electrochimica Acta 39(10): 1451-1452.
Mansfeld, F. (1995). "Use of Electrochemical Impedance Spectroscopy for the Study of
Corrosion Protection by Polymer-Coatings." Journal of Applied Electrochemistry
25(3): 187-202.
Mansfeld, F. (2006). Electrochemical Impedance Spectroscopy. Analytical Methods in
Corrosion Science and Engineering. P. Marcus and F. Mansfeld, CRC Press: 463-
505.
Mansfeld, F., Han, L. T., Lee, C. C. and Zhang, G. (1998). "Evaluation of Corrosion
Protection by Polymer Coatings Using Electrochemical Impedance Spectroscopy
and Noise Analysis." Electrochimica Acta 43(19-20): 2933-2945.
Mansfeld, F., Jeanjaquet, S. L. and Kendig, M. W. (1986). "An Electrochemical
Impedance Spectroscopy Study of Reactions at the Metal-Coating Interface."
Corrosion Science 26(9): 735-742.
Mansfeld, F., Lin, S., Kim, S. and Shih, H. (1989). "Surface Modification of Al Alloys
and Al-Based Metal Matrix Composites by Chemical Passivation."
Electrochimica Acta 34(8): 1123-1132.
Mansfeld, F. and Tsai, C. H. (1991). "Determination of Coating Deterioration with Eis .1.
Basic Relationships." Corrosion 47(12): 958-963.
Mansfeld, F., Tsai, C. H. and Shih, H. (1992a). ASTM STP 186: 1154.

135
Mansfeld, F., Wang, Y. and Shih, H. (1992b). "The Ce---Mo Process for the
Development of a Stainless Aluminum." Electrochimica Acta 37(12): 2277-2282.
Rangel, C. M. and Travassos, M. A. (1992). "The Passivation of Aluminium in Lithium
Carbonate/Bicarbonate Solutions." Corrosion Science 33(3): 327-343.
Schweitzer, P. A. (2006). Paint and Coatings - Application and Corrosion Resistance,
CRC Taylor and Francis.
Song, Y. B. and Chin, D. T. (2002). "Current Efficiency and Polarization Behavior of
Trivalent Chromium Electrodeposition Process." Electrochimica Acta 48(4): 349-
356.
SurTec International. "Product Info.".
Titz, J., Wagner, G. H., Spahn, H., Ebert, M., Juttner, K. and Lorenz, W. J. (1990).
"Characterization of Organic Coatings on Metal Substrates by Electrochemical
Impedance Spectroscopy." Corrosion 46(3): 221-229.
Tsai, C. H. (1992). The Application of Electrochemical Impedance Spectroscopy in the
Study of Polymer Coatings and Biofilms, University of Southern California. PhD.
Waldrop, J. R. and Kendig, M. W. (1998). "Nucleation of Chromate Conversion Coating
on Aluminum 2024-T3 Investigated by Atomic Force Microscopy." Journal of
The Electrochemical Society 145(1): L11-L13.
Wang, Y. (1994). Corrosion Protection of Aluminum Alloys by Surface Modification
Using Chromate Free Approaches, University of Southern California. PhD Thesis.
Xingwen, Y., Chunan, C., Zhiming, Y., Derui, Z. and Zhongda, Y. (2001). "Study of
Double Layer Rare Earth Metal Conversion Coating on Aluminum Alloy Ly12."
Corrosion Science 43(7): 1283-1294.
Yu, H., Chen, B., Wu, H., Sun, X. and Li, B. (2008a). "Improved Electrochemical
Performance of Trivalent-Chrome Coating on Al 6063 Alloy Via Urea and
Thiourea Addition." Electrochimica Acta 54(2): 720-726.
Yu, H. C., Chen, B. Z., Shi, X. C., Sun, X. L. and Li, B. (2008b). "Investigation of the
Trivalent-Chrome Coating on 6063 Aluminum Alloy." Materials Letters 62(17-
18): 2828-2831.

136
Zarras, P. (2010). Private Communication. F. Mansfeld and A. Manohar.
Zeng, Z. X., Wang, L. P., Liang, A. M. and Zhang, J. Y. (2006). "Tribological and
Electrochemical Behavior of Thick Cr-C Alloy Coatings Electrodeposited in
Trivalent Chromium Bath as an Alternative to Conventional Cr Coatings."
Electrochimica Acta 52(3): 1366-1373.

137
Bibliography

Aaron, D., Tsouris, C., Hamilton, C. Y. and Borole, A. P. (2010). "Assessment of the
Effects of Flow Rate and Ionic Strength on the Performance of an Air-Cathode
Microbial Fuel Cell Using Electrochemical Impedance Spectroscopy." Energies
3(4): 592-606.
Aelterman, P., Rabaey, K., Pham, H. T., Boon, N. and Verstraete, W. (2006).
"Continuous Electricity Generation at High Voltages and Currents Using Stacked
Microbial Fuel Cells." Environmental Science & Technology. 40(10): 3388-3394.
Apte, A. D., Tare, V. and Bose, P. (2006). "Extent of Oxidation of Cr(Iii) to Cr(Vi) under
Various Conditions Pertaining to Natural Environment." Journal of Hazardous
Materials 128(2-3): 164-174.
Arnott, D. R., Hinton, B. R. W. and Ryan, N. E. (1989). "Cationic-Film-Forming
Inhibitors for the Protection of the Aa-7075 Aluminum-Alloy against Corrosion in
Aqueous Chloride Solution." Corrosion 45(1): 12-18.
Aziz, P. M. and Godard, H. P. (1952). "Pitting Corrosion Characteristics of Aluminum -
Influence of Magnesium and Manganese." Industrial & Engineering Chemistry
44(8): 1791-1795.
Bennetto, H. P., John, L. S., Kazuko, T. and Carmen, A. V. (1983). "Anodic Reactions in
Microbial Fuel Cells." Biotechnology and Bioengineering 25(2): 559-568.
Berger, R., Bexell, U., Grehk, T. M. and Hornstrom, S. E. (2007). "A Comparative Study
of the Corrosion Protective Properties of Chromium and Chromium Free
Passivation Methods." Surface & Coatings Technology 202: 391-397.
Bond, D. R. and Lovley, D. R. (2003). "Electricity Production by Geobacter
Sulfurreducens Attached to Electrodes." Appl. Environ. Microbiol. 69(3): 1548-
1555.
Bond, D. R., Holmes, D. E., Tender, L. M. and Lovley, D. R. (2002). "Electrode-
Reducing Microorganisms That Harvest Energy from Marine Sediments." Science
295(5554): 483-485.

138
Borole, A. P., Aaron, D., Hamilton, C. Y. and Tsouris, C. (2010). "Understanding Long-
Term Changes in Microbial Fuel Cell Performance Using Electrochemical
Impedance Spectroscopy." Environmental Science & Technology 44(7): 2740-
2744.
Bretschger, O. (2008). Electron Transfer Capability and Metabolic Processes of the
Genus Shewanella with Applications to the Optimization of Microbial Fuel Cells,
University of Southern California. PhD Thesis.
Bretschger, O., Cheung, A. C. M., Mansfeld, F. and Nealson, K. H. (2010). "Comparative
Microbial Fuel Cell Evaluations of Shewanella Spp." Electroanalysis 22(7-8):
883-894.
Bretschger, O., Obraztsova, A., Sturm, C. A., Chang, I. S., Gorby, Y. A., Reed, S. B.,
Culley, D. E., Reardon, C. L., Barua, S., Romine, M. F., Zhou, J., Beliaev, A. S.,
Bouhenni, R., Saffarini, D., Mansfeld, F., Kim, B. H., Fredrickson, J. K. and
Nealson, K. H. (2007). "Current Production and Metal Oxide Reduction by
Shewanella Oneidensis MR-1 Wild Type and Mutants." Applied and
Environmental Microbiology 73: 7003-7012.
Buchheit, R. G., Bode, M. D. and Stoner, G. E. (1994). "Corrosion-Resistant, Chromate-
Free Talc Coatings for Aluminum." Corrosion 50(3): 205-214.
Burns, R. M. and Bradley, W. W. (1967). Protective Coatings for Metals, Reinhold
Publishing Corporation.
Cai, M., Liu, J. and Wei, Y. (2004). "Enhanced Biohydrogen Production from Sewage
Sludge with Alkaline Pretreatment." Environmental Science & Technology
38(11): 3195-3202.
Chaudhuri, S. K. and Lovley, D. R. (2003). "Electricity Generation by Direct Oxidation
of Glucose in Mediatorless Microbial Fuel Cells." Nat Biotech 21(10): 1229.
Clauwaert, P., Rabaey, K., Aelterman, P., De Schamphelaire, L., Ham, T. H., Boeckx, P.,
Boon, N. and Verstraete, W. (2007a). "Biological Denitrification in Microbial
Fuel Cells." Environmental Science & Technology 41(9): 3354-3360.

139
Clauwaert, P., van der Ha, D., Boon, N., Verbeken, K., Verhaege, M., Rabaey, K. and
Verstraete, W. (2007b). "Open Air Biocathode Enables Effective Electricity
Generation with Microbial Fuel Cells." Environmental Science & Technology
41(21): 7564-7569.
Cooper, K. R. and Smith, M. (2006). "Electrical Test Methods for on-Line Fuel Cell
Ohmic Resistance Measurement." Journal of Power Sources 160(2): 1088-1095.
Davis, J. R. (1999). Corrosion of Aluminum and Aluminum Alloys, ASM International.
Deft Inc. "Product Information Data Sheet."
El-Naggar, M. Y., Gorby, Y. A., Xia, W., Nealson, K. H., (2008), “The Molecular
Density of States in Bacterial Nanowires”, Biophysical Journal 95(1): L10-L12.
Fan, Y., Hu, H. and Liu, H. (2007). "Enhanced Coulombic Efficiency and Power Density
of Air-Cathode Microbial Fuel Cells with an Improved Cell Configuration."
Journal of Power Sources 171(2): 348-354.
Fricke, K., Harnisch, F. and Schroder, U. (2008). "On the Use of Cyclic Voltammetry for
the Study of Anodic Electron Transfer in Microbial Fuel Cells." Energy &
Environmental Science 1(1): 144-147.
Gomadam, P. M. and Weidner, J. W. (2005). "Analysis of Electrochemical Impedance
Spectroscopy in Proton Exchange Membrane Fuel Cells." International Journal of
Energy Research 29(12): 1133-1151.
Gorby, Y. A., Yanina, S., McLean, J. S., Rosso, K. M., Moyles, D., Dohnalkova, A.,
Beveridge, T. J., Chang, I. S., Kim, B. H., Kim, K. S., Culley, D. E., Reed, S. B.,
Romine, M. F., Saffarini, D.A., Hill, E. A., Shi, L., Elias, D. A., Kennedy, D. W.,
Pinchuk, G., Watanabe, K., Ishii, S., Logan, B., Nealson, K. H., Fredrickson, J. K.,
(2006), “Electrically conductive bacterial nanowires produced by Shewanella
oneidensis strain MR-1 and other microorganisms”, PNAS 103(30): 11358-11363.
Gregory, K. B. and Lovley, D. R. (2005). "Remediation and Recovery of Uranium from
Contaminated Subsurface Environments with Electrodes." Environmental Science
& Technology 39(22): 8943-8947.
Hamman, C. H., Hamnett, A. and Vielstich, W. (2007). Electrochemistry, Wiley - VCH.

140
He, Z. and Angenent, L. T. (2006). "Application of Bacterial Biocathodes in Microbial
Fuel Cells." Electroanalysis 18(19-20): 2009-2015.
He, Z. and Mansfeld, F. (2009). "Exploring the Use of Electrochemical Impedance
Spectroscopy (EIS) in Microbial Fuel Cell Studies." Energy & Environmental
Science 2(2): 215-219.
He, Z., Huang, Y., Manohar, A. K. and Mansfeld, F. (2008). "Effect of Electrolyte pH on
the Rate of the Anodic and Cathodic Reactions in an Air-Cathode Microbial Fuel
Cell." Bioelectrochemistry 74(1): 78-82.
He, Z., Shao, H. B. and Angenent, L. T. (2007). "Increased Power Production from a
Sediment Microbial Fuel Cell with a Rotating Cathode." Biosensors &
Bioelectronics 22: 3252-3255.
He, Z., Wagner, N., Minteer, S. D. and Angenent, L. T. (2006). "An Upflow Microbial
Fuel Cell with an Interior Cathode: Assessment of the Internal Resistance by
Impedance Spectroscopy." Environmental Science & Technology 40(17): 5212-
5217.
Heitz, E. and Kreysa, G. (1986). Priciples of Electrochemical Engineering, VCH.
Henkel International. "Technical Data Sheet.".
Hinton, B. R. W. (1992). "Corrosion Inhibition with Rare-Earth-Metal Salts." Journal of
Alloys and Compounds 180: 15-25.
Hjelm, A. K. and Lindbergh, G. (2002). "Experimental and Theoretical Analysis of
LiMn
2
O
4
Cathodes for Use in Rechargeable Lithium Batteries by Electrochemical
Impedance Spectroscopy (EIS)." Electrochimica Acta 47(11): 1747-1759.
Jun, Z., Gerald, F. and Richard, L. M. (1998). "Corrosion Protection of Untreated Al-
2024-T3 in Chloride Solution by a Chromate Conversion Coating Monitored with
Raman Spectroscopy." Journal of The Electrochemical Society 145(7): 2258-2264.
Karube, I., Matsunaga, T., Tsuru, S. and Suzuki, S. (1976). "Continous Hydrogen
Production by Immobilized Whole Cells of Clostridium Butyricum." Biochimica
et Biophysica Acta (BBA) - General Subjects 444(2): 338-343.

141
Kendig, M. W. and Buchheit, R. G. (2003). "Corrosion Inhibition of Aluminum and
Aluminum Alloys by Soluble Chromates, Chromate Coatings, and Chromate-Free
Coatings." Corrosion 59(5): 379-400.
Kendig, M., Jeanjaquet, S., Addison, R. and Waldrop, J. (2001). "Role of Hexavalent
Chromium in the Inhibition of Corrosion of Aluminum Alloys." Surface and
Coatings Technology 140(1): 58-66.
Kim, B. H., Chang, I. S., Cheol Gil, G., Park, H. S. and Kim, H. J. (2003). "Novel BOD
(Biological Oxygen Demand) Sensor Using Mediator-Less Microbial Fuel Cell."
Biotechnology Letters 25(7): 541.
Kim, B. H., Park, H. S., Kim, H. J., Kim, G. T., Chang, I. S., Lee, J. and Phung, N. T.
(2004). "Enrichment of Microbial Community Generating Electricity Using a
Fuel-Cell-Type Electrochemical Cell." Applied Microbiology and Biotechnology
63(6): 672.
Kus, E. (2006). An Electrochemical Evaluation of New Materials and Methods for
Corrosion Protection, University of Southern California. PhD Thesis.
Liu, H., Grot, S. and Logan, B. E. (2005). "Electrochemically Assisted Microbial
Production of Hydrogen from Acetate." Environmental Science & Technology.
39(11): 4317-4320.
Logan, B. E., Hamelers, B., Rozendal, R., Schroder, U., Keller, J., Freguia, S., Aelterman,
P., Verstraete, W. and Rabaey, K. (2006). "Microbial Fuel Cells: Methodology
and Technology." Environmental Science & Technology. 40(17): 5181-5192.
Manohar, A. K., He, Z. and Mansfeld, F. (2009). The Use of Electrochemical Impedance
Spectroscopy (EIS) for the Evaluation of the Electrochemical Properties of
Microbial Fuel Cells. Bioelectrochemical Systems from Extracellular Electron
Transfer to Biotechnological Application. K. Rabaey, L. T. Angenent, U.
Schroder and J. Keller, IWA Publishing.
Mansfeld, F. (1990). "Electrochemical Impedance Spectroscopy (EIS) as a New Tool for
Investigating Methods of Corrosion Protection." Electrochimica Acta 35(10):
1533-1544.

142
Mansfeld, F. (1994). "Determination of the Reactive Area of Organic Coated Metals -
Physical Meaning and Limits of the Break-Point Method - Discussion."
Electrochimica Acta 39(10): 1451-1452.
Mansfeld, F. (1995). "Use of Electrochemical Impedance Spectroscopy for the Study of
Corrosion Protection by Polymer-Coatings." Journal of Applied Electrochemistry
25(3): 187-202.
Mansfeld, F. (2005). "Tafel Slopes and Corrosion Rates Obtained in the Pre-Tafel Region
of Polarization Curves." Corrosion Science 47(12): 3178-3186.
Mansfeld, F. (2006). “Electrochemical Impedance Spectroscopy”, Analytical Methods in
Corrosion Science and Engineering. P. Marcus and F. Mansfeld, CRC Press: 463-
505.
Mansfeld, F. (2006a). "Classic Paper in Corrosion Science and Engineering with a
Perspective by F. Mansfeld." Corrosion 62(10): 843-844.
Mansfeld, F. (2006b). Electrochemical Impedance Spectroscopy. Analytical Methods in
Corrosion Science and Engineering. P. Marcus and F. Mansfeld, CRC Press: 463-
505.
Mansfeld, F. (2007a). “An Evaluation of a Microbial Fuel Cell Using Different
Electrochemical Techniques”. 7th International Symposium on Electrochemical
Impedance Spectroscopy, June 3 - 8, 2007, Argelès-sur-Mer, France.
Mansfeld, F. (2007b). "The Interaction of Bacteria and Metal Surfaces." Electrochimica
Acta 52(27): 7670-7680.
Mansfeld, F. (2009). "Fundamental Aspects of the Polarization Resistance Technique-the
Early Days." Journal of Solid State Electrochemistry 13(4): 515-520.
Mansfeld, F. and Kendig, M. W. (1985). "Electrochemical Impedance Spectroscopy of
Protective Coatings." Materials and Corrosion/Werkstoffe und Korrosion 36(11):
473-483.
Mansfeld, F. and Tsai, C. H. (1991). "Determination of Coating Deterioration with EIS .1.
Basic Relationships." Corrosion 47(12): 958-963.

143
Mansfeld, F., Han, L. T., Lee, C. C. and Zhang, G. (1998). "Evaluation of Corrosion
Protection by Polymer Coatings Using Electrochemical Impedance Spectroscopy
and Noise Analysis." Electrochimica Acta 43(19-20): 2933-2945.
Mansfeld, F., Jeanjaquet, S. L. and Kendig, M. W. (1986). "An Electrochemical
Impedance Spectroscopy Study of Reactions at the Metal-Coating Interface."
Corrosion Science 26(9): 735-742.
Mansfeld, F., Lin, S., Kim, S. and Shih, H. (1989). "Surface Modification of Al Alloys
and Al-Based Metal Matrix Composites by Chemical Passivation."
Electrochimica Acta 34(8): 1123-1132.
Mansfeld, F., Shih, H., Greene, H. and Tsai, C. H. (1993). ASTM STP 37: 1188.
Mansfeld, F., Tsai, C. H. and Shih, H. (1992). ASTM STP 186: 1154.
Mansfeld, F., Wang, Y. and Shih, H. (1992b). "The Ce---Mo Process for the
Development of a Stainless Aluminum." Electrochimica Acta 37(12): 2277-2282.
Min, B. and Logan, B. E. (2004). "Continuous Electricity Generation from Domestic
Wastewater and Organic Substrates in a Flat Plate Microbial Fuel Cell."
Environmental Science & Technology 38(21): 5809-5814.
Min, B., Kim, J. R., Oh, S. E., Regan, J. M. and Logan, B. E. (2005). "Electricity
Generation from Swine Wastewater Using Microbial Fuel Cells." Water Research
39(20): 4961-4968.
Niessen, J., Schröder, U., Rosenbaum, M. and Scholz, F. (2004). "Fluorinated
Polyanilines as Superior Materials for Electrocatalytic Anodes in Bacterial Fuel
Cells." Electrochemistry Communications 6(6): 571-575.
Oldham, K. B. and Mansfeld, F. (1973). "Corrosion Rates from Polarization Curves -
New Method." Corrosion Science 13(10): 813-819.
Ouitrakul, S., Sriyudthsak, M., Charojrochkul, S. and Kakizono, T. (2007). "Impedance
Analysis of Bio-Fuel Cell Electrodes." Biosensors & Bioelectronics 23(5): 721-
727.

144
Park, D. H. and Zeikus, G. J. (2002). "Impact of Electrode Composition on Electricity
Generation in a Single-Compartment Fuel Cell Using Shewanella Putrefaciens."
Applied Microbiology and Biotechnology 59(1): 58.
Park, D. H. and Zeikus, G. J. (2003). "Improved Fuel Cell and Electrode Designs for
Producing Electricity from Microbial Degradation." Biotechnology and
Bioengineering 81(3): 348-355.
Park, D. H., Kim, S. K., Shin, I. H. and Jeong, Y. J. (2000). "Electricity Production in
Biofuel Cell Using Modified Graphite Electrode with Neutral Red."
Biotechnology Letters 22(16): 1301-1304.
Park, H. S., Kim, B. H., Kim, H. S., Kim, H. J., Kim, G. T., Kim, M., Chang, I. S., Park,
Y. K. and Chang, H. I. (2001). "A Novel Electrochemically Active and Fe(III)-
Reducing Bacterium Phylogenetically Related to Clostridium Butyricum Isolated
from a Microbial Fuel Cell." Anaerobe 7(6): 297.
Pham, C. A., Jung, S. J., Phung, N. T., Lee, J., Chang, I. S., Kim, B. H., Yi, H. and Chun,
J. (2003). "A Novel Electrochemically Active and Fe(Iii)-Reducing Bacterium
Phylogenetically Related to Aeromonas Hydrophila, Isolated from a Microbial
Fuel Cell." FEMS Microbiology Letters 223(1): 129.
Prasad, D., Arun, S., Murugesan, A., Padmanaban, S., Satyanarayanan, R. S., Berchmans,
S. and Yegnaraman, V. (2007). "Direct Electron Transfer with Yeast Cells and
Construction of a Mediatorless Microbial Fuel Cell." Biosensors & Bioelectronics
22(11): 2604-2610.
Qiao, Y., Li, C. M., Bao, S. J. and Bao, Q. L. (2007). "Carbon Nanotube/Polyaniline
Composite as Anode Material for Microbial Fuel Cells." Journal of Power
Sources 170(1): 79-84.
Rabaey, K., Boon, N., Siciliano, S. D., Verhaege, M. and Verstraete, W. (2004). "Biofuel
Cells Select for Microbial Consortia That Self-Mediate Electron Transfer."
Applied and Environmental Microbiology 70(9): 5373-5382.
Ramasamy, R. P., Gadhamshetty, V., Nadeau, L. J. and Johnson, G. R. (2009).
"Impedance Spectroscopy as a Tool for Non-Intrusive Detection of Extracellular
Mediators in Microbial Fuel Cells." Biotechnology and Bioengineering 104(5):
882-891.

145
Ramasamy, R. P., Ren, Z. Y., Mench, M. M. and Regan, J. M. (2008). "Impact of Initial
Biofilm Growth on the Anode Impedance of Microbial Fuel Cells."
Biotechnology and Bioengineering 101(1): 101-108.
Rangel, C. M. and Travassos, M. A. (1992). "The Passivation of Aluminium in Lithium
Carbonate/Bicarbonate Solutions." Corrosion Science 33(3): 327-343.
Rhoads, A., Beyenal, H. and Lewandowski, Z. (2005). "Microbial Fuel Cell Using
Anaerobic Respiration as an Anodic Reaction and Biomineralized Manganese as a
Cathodic Reactant." Environmental Science & Technology 39(12): 4666-4671.
Schweitzer, P. A. (2006). Paint and Coatings - Application and Corrosion Resistance,
CRC Taylor and Francis.
Shih, H. and Mansfeld, F. (1992). ASTM STP. 1154: 174.
Sibel, D. R., Bennetto, H. P., Gerard, M. D., Jeremy, R. M., John, L. S. and Christopher,
F. T. (1984). "Electron-Transfer Coupling in Microbial Fuel Cells: 1. Comparison
of Redox-Mediator Reduction Rates and Respiratory Rates of Bacteria." Journal
of chemical technology and biotechnology. Biotechnology 34(1): 3-12.
Song, Y. B. and Chin, D. T. (2002). "Current Efficiency and Polarization Behavior of
Trivalent Chromium Electrodeposition Process." Electrochimica Acta 48(4): 349-
356.
Srikanth, S., Marsili, E., Flickinger, M. C. and Bond, D. R. (2008). "Electrochemical
Characterization of Geobacter Sulfurreducens Cells Immobilized on Graphite
Paper Electrodes." Biotechnology and Bioengineering 99(5): 1065-1073.
SurTec International. "Product Info."
Taberna, P. L., Simon, P. and Fauvarque, J. F. (2003). "Electrochemical Characteristics
and Impedance Spectroscopy Studies of Carbon-Carbon Supercapacitors." Journal
of the Electrochemical Society 150(3): A292-A300.
Ter Heijne, A., Hamelers, H. V. M., De Wilde, V., Rozendal, R. A. and Buisman, C. J. N.
(2006). "A Bipolar Membrane Combined with Ferric Iron Reduction as an
Efficient Cathode System in Microbial Fuel Cells." Environmental Science &
Technology 40(17): 5200-5205.

146
Titz, J., Wagner, G. H., Spahn, H., Ebert, M., Juttner, K. and Lorenz, W. J. (1990).
"Characterization of Organic Coatings on Metal Substrates by Electrochemical
Impedance Spectroscopy." Corrosion 46(3): 221-229.
Tsai, C. H. (1992). The Application of Electrochemical Impedance Spectroscopy in the
Study of Polymer Coatings and Biofilms, University of Southern California. PhD
Thesis.
Waldrop, J. R. and Kendig, M. W. (1998). "Nucleation of Chromate Conversion Coating
on Aluminum 2024-T3 Investigated by Atomic Force Microscopy." Journal of
The Electrochemical Society 145(1): L11-L13.
Wang, Y. (1994). Corrosion Protection of Aluminum Alloys by Surface Modification
Using Chromate Free Approaches, University of Southern California. PhD Thesis.
Xingwen, Y., Chunan, C., Zhiming, Y., Derui, Z. and Zhongda, Y. (2001). "Study of
Double Layer Rare Earth Metal Conversion Coating on Aluminum Alloy Ly12."
Corrosion Science 43(7): 1283-1294.
Yokoyama, H., Ohmori, H., Ishida, M., Waki, M. and Tanaka, Y. (2006). "Treatment of
Cow-Waste Slurry by a Microbial Fuel Cell and the Properties of the Treated
Slurry as a Liquid Manure." Animal Science Journal 77(6): 634-638.
You, S. J., Zhao, Q. L., Zhang, J. N., Jiang, J. Q. and Zhao, S. Q. (2006). "A Microbial
Fuel Cell Using Permanganate as the Cathodic Electron Acceptor." Journal of
Power Sources 162(2): 1409-1415.
You, S. J., Zhao, Q. L., Zhang, J., Liu, H., Jiang, J. Q. and Zhao, S. Q. (2008). "Increased
Sustainable Electricity Generation in up-Flow Air-Cathode Microbial Fuel Cells."
Biosensors & Bioelectronics 23(7): 1157-1160.
You, S., Zhao, Q., Zhang, J., Jiang, J., Wan, C., Du, M. and Zhao, S. (2007). "A
Graphite-Granule Membrane-Less Tubular Air-Cathode Microbial Fuel Cell for
Power Generation under Continuously Operational Conditions." Journal of Power
Sources 173(1): 172-177.
Yu, H. C., Chen, B. Z., Shi, X. C., Sun, X. L. and Li, B. (2008b). "Investigation of the
Trivalent-Chrome Coating on 6063 Aluminum Alloy." Materials Letters 62(17-
18): 2828-2831.

147
Yu, H., Chen, B., Wu, H., Sun, X. and Li, B. (2008a). "Improved Electrochemical
Performance of Trivalent-Chrome Coating on Al 6063 Alloy Via Urea and
Thiourea Addition." Electrochimica Acta 54(2): 720-726.
Zarras, P. (2010). Private Communication. F. Mansfeld and A. Manohar.
Zeng, Z. X., Wang, L. P., Liang, A. M. and Zhang, J. Y. (2006). "Tribological and
Electrochemical Behavior of Thick Cr-C Alloy Coatings Electrodeposited in
Trivalent Chromium Bath as an Alternative to Conventional Cr Coatings."
Electrochimica Acta 52(3): 1366-1373.
Zhao, F., Harnisch, F., Schroder, U., Scholz, F., Bogdanoff, P. and Herrmann, I. (2006).
"Challenges and Constraints of Using Oxygen Cathodes in Microbial Fuel Cells."
Environmental Science & Technology. 40(17): 5193-5199.
Zhao, F., Harnisch, F., Schröder, U., Scholz, F., Bogdanoff, P. and Herrmann, I. (2005).
"Application of Pyrolysed Iron(Ii) Phthalocyanine and Cotmpp Based Oxygen
Reduction Catalysts as Cathode Materials in Microbial Fuel Cells."
Electrochemistry Communications 7(12): 1405-1410.
Zhao, F., Slade, R. C. T. and Varcoe, J. R. (2009). "Techniques for the Study and
Development of Microbial Fuel Cells: An Electrochemical Perspective."
Chemical Society Reviews 38(7): 1926-1939.

Abstract (if available)

Abstract The results of a detailed evaluation of the properties of the anode and the cathode of a mediator-less microbial fuel cell (MFC) and the factors determining the power output of the MFC using different electrochemical techniques are presented in Chapter 1. In the MFC under investigation, the biocatalyst - Shewanella oneidensis MR-1 - oxidizes the fuel and transfers the electrons directly into the anode which consists of graphite felt. Oxygen is reduced at the cathode which consists of Pt-plated graphite felt. A proton exchange membrane separates the anode and the cathode compartments. The electrolyte was a PIPES buffer solution and lactate was used as the fuel. Separate tests were performed with the buffer solution containing lactate and with the buffer solution with lactate and MR-1 as anolytes.

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Creator Manohar, Aswin Karthik (author)

Core Title Applications of advanced electrochemical techniques in the study of microbial fuel cells and corrosion protection by polymer coatings

School Viterbi School of Engineering

Degree Doctor of Philosophy

Degree Program Materials Science

Publication Date 11/22/2010

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag corrosion protection,electrochemical evaluation,microbial fuel cells,OAI-PMH Harvest

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Mansfeld, Florian B. (committee chair), Goo, Edward K. (committee member), Nealson, Kenneth H. (committee member)

Creator Email aswinkam@usc.edu,aswinkarthik@gmail.com

Permanent Link (DOI) https://doi.org/10.25549/usctheses-m3545

Unique identifier UC1301246

Identifier etd-Manohar-4183 (filename),usctheses-m40 (legacy collection record id),usctheses-c127-422316 (legacy record id),usctheses-m3545 (legacy record id)

Legacy Identifier etd-Manohar-4183.pdf

Dmrecord 422316

Document Type Dissertation

Rights Manohar, Aswin Karthik

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Repository Name Libraries, University of Southern California

Repository Location Los Angeles, California

Repository Email cisadmin@lib.usc.edu