Platinum (Pt) alloy nanoparticles are used as catalysts in electrochemical cells to
reduce oxygen to water and to oxidize hydrogen; the overall reaction converts chemical
energy into electrical energy. These nanocatalysts are deposited on a carbon substrate
and their catalytic function takes place in acid medium. This harsh environment causes
an undesired reaction, which is the dissolution of the metal atoms into the acid medium;
thus affecting the catalyst life. This dissertation aims to investigate the dissolution
mechanism of fuel cell cathode catalysts at the atomic level starting from the oxygen
reaction intermediates on the cathode catalyst surface and propose guidelines to improve
cathode catalysts durability based on our proposed mechanism. Density functional
theory is employed to study various possible scenarios with the goals of understanding
the mechanism of the metal atom dissolution process and establishing some guidelines
that permit a rational design of catalysts with better stability against dissolution. A
thermodynamic analysis of potential metal dissolution reactions in acid medium is
presented first, using density functional theory calculations to explore the relative
stabilities of transition metals in relation to that of Pt. The study is performed by
comparing the change in reaction Gibbs free energies for different metals in a given
dissolution reaction. Then, a series of density functional theory studies, tending to
investigate the adsorbed atomic oxygen absorption process from cathode catalyst surface
into its subsurface, includes: 1) the oxygen adsorption on various catalyst surfaces and
oxygen absorption in subsurface sites to figure out the minimum energy pathway and
energy barrier of on-surface oxygen migration and absorption into subsurface; 2) the oxygen coverage, the other oxygen reduction reaction intermediates, and water effects
on the oxygen absorption process according to reaction pathways, energy barriers, and
thermodynamic analysis; 3) the oxygen absorption process on several Pt-based alloys
with various compositions and components to find out the best alloy to inhibit atomic
oxygen absorption including both kinetic and thermodynamic analyses, and the effects
of such alloyed species on the inhibition process.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2458 |
| Date | 15 May 2009 |
| Creators | Gu, Zhihui |
| Contributors | Balbuena, Perla B |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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