Ethanol Oxidation on Carbon-Supported Pt, PtRu, and PtSn Catalysts Studied by Operando X-ray Absorption Spectroscopy

Operando X-ray absorption spectroscopy (XAS) has been used to study the adsorbates and structural changes and their dependence on potential, existing during the ethanol oxidation reaction (EOR) on carbon-supported Pt, PtRu, and PtSn anode catalysts. Conventional EXAFS was applied to identify nanoparticle structure and particle size. The Delta mu-XANES technique was used to investigate adsorbed species with potential. On pure Pt, an overall increase in Delta mu amplitude exists under EOR compared to that existing during the methanol oxidation reaction (MOR). This increased amplitude was attributed mainly to the C-1 species on the surface during the EOR; these C-1 species and CO become oxidized when O(H) come down on the surface. On PtRu catalysts, the O(H) formation and C-species oxidation begins at lower potentials compared to Pt. The ligand effect from oxidized RuOx islands is operative in PtRu and responsible for the performance enhancement. On PtSn, we observe O(H) at nearly all potentials, which may be explained by a very strong ligand effect involving SnOx. The operand Delta mu and EXAFS results enable the determination of relative active surface areas, particle structure, and adsorbate coverages with potential of C species, OH, and O providing new insights into the role of OH in the EOR.