Electro-oxidation of methanol on gold in alkaline media: Adsorption characteristics of reaction intermediates studied using time resolved electro-chemical impedance and surface plasmon resonance techniques

Electro-catalytic oxidation of methanol is the anode reaction in direct methanol fuel cells. We have studied the adsorption characteristics of the intermediate reactants of this multistep reaction on a gold film electrode in alkaline solutions by combining surface plasmon resonance (SPR) measurements with Fourier transform electro-chemical impedance spectroscopy (FT-EIS). Methanol oxidation in this system shows no significant effects of “site poisoning” by chemisorbed CO. Our results suggest that OH− chemisorbed onto Au acts as a stabilizing agent for the surface species of electro-active methanol. Double layer charging/discharging and adsorption/desorption of OH− show more pronounced effects than adsorption/oxidation of methanol in controlling the surface charge density of the Au substrate. These effects are manifested in both the EIS and the SPR data, and serve as key indicators of the surface reaction kinetics. The data presented here describe the important role of adsorbed OH− in electro-catalysis of methanol on Au, and demonstrate how SPR and FT-EIS can be combined for quantitative probing of catalytically active metal-solution interfaces.