Degree Type

Dissertation

Date of Award

2004

Degree Name

Doctor of Philosophy

Department

Chemical and Biological Engineering

First Advisor

Andrew C. Hillier

Abstract

Polymer electrolyte membrane fuel cells (PEMFCs) are compact power sources that can operate with high efficiencies and low emission of environmentally harmful gases. One of the major barriers impeding the development of PEMFCs as a competitive energy source is the inability of existing anode catalysts to oxidize fuels other than hydrogen at sufficient levels due to catalyst deactivation by carbon monoxide (CO) and other partial oxidation products. The focus of this research is the development and application of combinatorial strategies to construct and interrogate electrooxidation (anode) catalysts pertaining to PEMFCs to discover catalysts with enhanced performance in catalyst deactivating environments. A novel method (known as the "gel-transfer" method) for synthesizing catalyst composition gradient libraries for combinatorial catalyst discovery was developed. This method involved transferring a spatial concentration gradient of precursor metal salts created within a polymer gel on to a solid conducting substrate by electrochemical reduction. Chemically sensitive surface-imaging techniques, namely, scanning electrochemical microscopy (SECM) and optical screening with a pH-dependent fluorescence probe were used to characterize the combinatorial catalyst samples. The utility of SECM as a screening tool to measure the activity of multicomponent catalyst libraries towards fuel cell electrooxidation reactions was established with simple catalyst libraries including a platinum coverage gradient and platinum-ruthenium and platinum-ruthenium-molybdenum arrays. A platinum-ruthenium surface composition gradient was constructed through the gel-transfer method and its reactivity towards hydrogen oxidation in the presence of a catalyst poison (CO) was mapped using the SECM. Ruthenium composition between 20 and 30% exhibited superior performance than the rest of the binary. The gel-transfer method was extended to construct a ternary platinum-ruthenium-rhodium catalyst library and its reactivity towards several electrooxidation reactions including oxidation of hydrogen, CO, methanol and ethanol was mapped using a pH-sensitive fluorescent probe. Trends in reactivity for these reactions as a function of catalyst composition were determined. Future directions of this research are also presented.

DOI

https://doi.org/10.31274/rtd-180813-14305

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu

Copyright Owner

Shrisudersan Jayaraman

Language

en

Proquest ID

AAI3145650

File Format

application/pdf

File Size

193 pages

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