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AN ELECTROCHEMICAL EVALUATION OF RUTHENIUM-BASED
ELECTROCATALYSTS FOR OXYGEN EVOLUTION
by
Thomas I. Valdez
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 Thomas I. Valdez
Object Description
| Title | An electrochemical evaluation of ruthenium-based electrocatalysts for oxygen evolution |
| Author | Valdez, Thomas I. |
| Author email | tivaldez@usc.edu; tivaldez@ca.rr.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Materials Science & Engineering |
| School | Viterbi School of Engineering |
| Date defended/completed | 2010-12 |
| Date submitted | 2010 |
| Restricted until | Unrestricted |
| Date published | 2010-12-09 |
| Advisor (committee chair) | Mansfeld, Florian B. |
| Advisor (committee member) |
Goo, Edward K. Prakash, G.K. Surya |
| Abstract | A study of ruthenium oxide-based oxygen evolution catalysts for use in proton exchange membrane (PEM) electrolyzers was performed. In this work, oxygen evolution catalysts were fabricated via sol-gel, high energy ball milling, and thermal processing techniques. Thermal analysis techniques such as differential scanning calorimetry (DSC), differential thermal analysis (DTA), and thermal gravimetric analysis (TGA) were used to determine the optimum processing temperatures to be used for catalysts fabrication and annealing. The materials properties of the catalysts were studied with scanning electron microscopy, energy dispersive analysis (EDAX), X-ray diffraction, and X-ray photo-electron spectroscopy.; Electrodes were fabricated from the oxygen evolution catalysts and tested in electrolysis and three-electrode cells. The catalysts fabricated via sol-gel techniques included a ruthenium oxide and an iridium-ruthenium oxide catalyst. Three families of the thermally processed catalysts were developed: iridium-ruthenium oxide, lead-ruthenium oxide, and tin ruthenium oxide. A lead oxide: ruthenium oxide catalyst was fabricated via high energy ball-milling to be used as a fabrication comparison to the thermally processed catalysts.; The electrochemical evaluations for the oxygen evolution catalysts fabricated as electrolysis cells included current-step polarization and constant current electrolysis. The current step polarization experiments were used to determine the relative performance of the catalysts as well as to determine the kinetic parameters for the oxygen evolution reaction. The constant-current electrolysis experiments were used to estimate the degradation of the catalysts during operation. In these studies, it was determined that the thermal processing technique could produce stable and high performing catalysts. The thermally processed iridium ruthenium oxide catalysts with 9 to 12 mole percent iridium had the lowest overpotential for oxygen evolution of the electrolysis cells tested.; The electrochemical evaluation of the oxygen evolution catalysts in the three electrode cell included potentiodynamic and electrochemical impedance spectroscopy (EIS) studies. The potentiodynamic polarization studies were used to rank the relative performance of catalysts being studied. The EIS studies were also used to rank the relative performance as well as to provide an estimate of the electrochemically active surface area of the catalysts. The three families of thermally processed catalysts were studied in the three-electrode cell. The results of these studies include identifying that the mechanism of oxygen evolution changed when ruthenium oxide was thermally processed with iridium and lead. Iridium, lead, and tin were all found to stabilize ruthenium oxide at oxygen evolution potentials. The three-electrode cell studies confirmed that the thermally processed iridium-ruthenium oxide with 12 mole percent iridium was the superior catalysts for oxygen evolution. |
| Keyword | catalysis; electrolysis; oxygen evolution; oxygen generation; proton exchange membrane; ruthenium oxide |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m3594 |
| Contributing entity | University of Southern California |
| Rights | Valdez, Thomas I. |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | cisadmin@dots.usc.edu |
| Filename | etd-Valdez-4201 |
| Archival file | uscthesesreloadpub_Volume14/etd-Valdez-4201.pdf |
Description
| Title | Page 1 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@dots.usc.edu |
| Full text | AN ELECTROCHEMICAL EVALUATION OF RUTHENIUM-BASED ELECTROCATALYSTS FOR OXYGEN EVOLUTION by Thomas I. Valdez 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 Thomas I. Valdez |
