Ensemble Site Requirements for Oxidative Adsorption
of Methanol and Ethanol on Pt Membrane Electrode Assemblies
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Abstract
The ensemble site requirements for the oxidative adsorption of
methanol and ethanol on platinum based membrane electrode assemblies
in operating liquid feed fuel cells were measured by CO stripping
voltammetry. At 30 °C and 0.2 V vs reference hydrogen electrode
(RHE), the CO<sub>ads</sub> coverage from directly dosed CO (CO<sub>CO</sub>), methanol (CO<sub>MeOH</sub>), and ethanol (CO<sub>EtOH</sub>) are 94%, 49%, and 39%, respectively. At 50 °C the CO<sub>MeOH</sub> and CO<sub>EtOH</sub> approach equality. The ratio of CO<sub>EtOH</sub>/CO<sub>MeOH</sub> was simulated with assumed ensemble site requirements
of 3 and 2 for ethanol and methanol respectively. Experimental and
simulated ratios of 0.79 and 0.78 suggest that high surface area fuel
cell Pt catalysts at 30 °C have adsorption properties similar
to that of a Pt (100) surface. Potential dependent infrared spectroscopy
of CO<sub>MeOH</sub> and CO<sub>EtOH</sub> from flash evaporated aqueous
alcohols delivered to a 50 °C fuel cell show lower CO<sub>EtOH</sub> relative to CO<sub>MeOH</sub> with Stark tuning rates below 10 cm<sup>–1</sup>/V
