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

Potentiodynamic broadband sum-frequency generation and electrochemistry were used to elucidate the mechanism of ethanol electrooxidation on polycrystalline platinum in acidic electrolytes. [Display omitted] ► 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 –CH x . ► –CH x is difficult to oxidize. ► Electrolyte anions affect adsorption of intermediates CO and acetate. 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 H 2SO 4 and HClO 4 solutions. However, CO molecules on bridge sites and sulfuric acid anions are found in H 2SO 4 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 ( 12CH 3 13CH 2OH) reveal information on the carbon–carbon bond cleavage and the subsequent CO formation. In particular, the methyl fragment (– 12CH x ) produces far less 12CO and suggests methyl electroreduction to methane and/or the persistence of –CH x on the Pt surface.