Reaction pathways of ethanol electrooxidation on polycrystalline platinum catalysts in acidic electrolytes

Ethanol electrooxidation reaction (EOR) pathways on polycrystalline platinum were studied with broadband sum-frequency generation (BB-SFG) spectroscopy and electrochemistry in unprecedented detail and under working fuel cell conditions. We present the first observation of adsorbed acetate and co-adsorbed sulfuric acid anions with SFG and a discussion of their relation to the EOR. Surface-adsorbed intermediates such as CO on Pt atop sites and acetate are observed in both H2SO4 and HClO4 solutions. However, CO molecules on bridge sites and sulfuric acid anions are found in H2SO4 only. At E < 0.5 V vs. Ag/AgCl, CO is the predominantly adsorbed species. Increasing the potential to E > 0.5 V results in the oxidative removal of CO and the adsorption of acetate anions. Experiments with isotopically labeled ethanol (12CH313CH2OH) reveal information on the carbon–carbon bond cleavage and the subsequent CO formation. In particular, the methyl fragment (–12CHx) produces far less 12CO and suggests methyl electroreduction to methane and/or the persistence of –CHx on the Pt surface.

Potentiodynamic broadband sum-frequency generation and electrochemistry were used to elucidate the mechanism of ethanol electrooxidation on polycrystalline platinum in acidic electrolytes.Figure optionsDownload high-quality image (49 K)Download as PowerPoint slideResearch highlights
► Electrocatalysis of ethanol on polycrystalline Pt surfaces.
► Reaction pathways revealed by sum-frequency generation (SFG) and electrochemistry.
► Surfaces-adsorbed intermediates include CO, acetate, and methyl fragment of ethanol produces –CHx.
► –CHx is difficult to oxidize.
► Electrolyte anions affect adsorption of intermediates CO and acetate.