Electrochemical investigation of organic cation adsorption onto hydrogen oxidation reaction catalysts in hydroxide exchange membrane fuel cells
| Author(s) | Woodroof, Mariah | |
| Date Accessioned | 2017-03-23T13:17:46Z | |
| Date Available | 2017-03-23T13:17:46Z | |
| Publication Date | 2016 | |
| Abstract | Fuel cells, a promising automotive power source, eliminate carbon emissions by converting hydrogen’s chemical potential directly into electricity by separating the hydrogen oxidation reaction (HOR) and oxygen reduction reaction with an ion exchange membrane (IEM). One type of IEMs, a hydroxide exchange membranes (HEM), allows the use of inexpensive platinum-group metal (PGM)-free catalysts. However, HEMs have low durability, and PGM-free catalysts that meet platinum’s HOR performance have not yet been developed. This thesis contributes to the development of durable HEMs and PGM-free HOR catalysts. ☐ A catalyst’s HOR properties are traditionally measured in liquid electrolyte. However, in a fuel cell catalysts are interfaced with a solid polymeric electrolyte with conductive cationic side chains. In this thesis, the HOR activity is measured for platinum interfaced with a HEM, or a solid base electrolyte (SBE), and is compared, for the first time, to the activity in a liquid base electrolyte (LBE). It was found that the measured activities for platinum in the LBE and SBE systems are equivalent. ☐ However, it was also found that platinum’s active surface area (SA) and H-adsorption potentials were reduced in the SBE. To understand this effect, platinum’s HOR activity in LBE with benzyltrimethylammonium (BTMA+)—an organic cation commonly used conductive sidechains of SBEs—and its individual components, benzene and tetramethylammonium (TMA+) was investigated. It was found that the phenyl group of BTMA+ adsorbs onto platinum’s surface within the potentials of H-adsorption, and the TMA+ component, although not physically adsorbed, blocks hydrogen diffusion to the surface. Therefore, BTMA + adsorption reduces platinum’s active SA and HOR activity through two mechanisms. ☐ A similar study of BTMA+ adsorption onto PGM-free catalysts is also needed since the goal is to eliminate platinum from HEM fuel cells. This thesis reports the interaction of an organic cation with a nickel-molybdenum (NiMo) HOR catalyst. Unlike for platinum, it was found that BTMA+ does not chemically adsorb onto NiMo and does not significantly affect the HOR. Therefore interactions between Ni-based catalysts and SBEs are of minimal concern for HEM development. This thesis concludes with suggested studies to further understand BTMA+ adsorption, including thermodynamic modeling and adsorption spectroscopy. | en_US |
| Advisor | Yan, Yushan | |
| Degree | Ph.D. | |
| Department | University of Delaware, Department of Chemical and Biomolecular Engineering | |
| Unique Identifier | 978291809 | |
| URL | http://udspace.udel.edu/handle/19716/21161 | |
| Publisher | University of Delaware | en_US |
| URI | https://search.proquest.com/docview/1868414168?accountid=10457 | |
| Title | Electrochemical investigation of organic cation adsorption onto hydrogen oxidation reaction catalysts in hydroxide exchange membrane fuel cells | en_US |
| Type | Thesis | en_US |