Ethanol Electrooxidation on an Island-Like Nanoporous Gold/Palladium Electrocatalyst in Alkaline Media: Electrocatalytic Properties and an In Situ Surface-Enhanced Raman Spectroscopy Study.

Abstract

The design of electrocatalysts with high activity and the understanding of the reaction mechanism for the ethanol oxidation reaction (EOR) are pivotal for commercializing direct ethanol fuel cells (DEFCs). Herein, island-like nanoporous gold/palladium (INPG/Pd) is designed as a highly efficient EOR electrocatalyst. For a better understanding of the reaction mechanism, in situ surface-enhanced Raman spectroscopy (SERS) in conjunction with H-D isotope replacement is used to investigate the dissociation and oxidation of CH3CH2OH on the INPG/Pd electrode, with a focus on identifying significant intermediate species in the reaction process. The results show that INPG/Pd has a higher electrocatalytic performance than INPG and indium-tin oxide (ITO) glass/palladium (Pd) due to the synergistic effect of NPG and Pd. INPG/Pd-10 shows the highest specific activity, the strongest charge-transfer ability, and relatively good stability. INPG/Pd presents better SERS sensitivity than ITO glass/Pd because of the plasma enhancement effect of nanoporous Au. The in situ Raman spectral results suggest that the oxidation of ethanol proceeds via a dual-pathway (C1 and C2) reaction mechanism. Dehydrogenation of ethanol can form acetaldehyde (CH3CHO) at -0.4 V. Meanwhile, the adsorbed acetaldehyde is oxidized to acetate from approximately -0.4 V, with the potential moving positively, which is the so-called C2 pathway. Alternatively, in the C1 pathway, CH3CHO and CH3CH2OH decomposed to intermediate species (adsorbed CO) on the INPG/Pd electrode due to C-C bond breaking at potentials of approximately -0.2 V. Subsequently, the CO species is oxidized to CO2 at more positive potentials.