Methanol Electro-Oxidation on the Pt Surface: Revisiting the Cyclic Voltammetry Interpretation

Methanol is a promising fuel for direct methanol fuel cells in portable devices. A deeper understanding of its electro-oxidation is needed for evaluating electrocatalytic performance and catalyst design. Here we provide an in-depth investigation of the cyclic voltammetry (CV) of methanol electro-oxidation. The oxidation peak in backward scan is shown to be unrelated to residual intermediate oxidation. The origin of the second oxidation peak (I-f2) is expected to the methanol oxidation on Pt-O-x. Electrochemical impedance spectroscopy coupled with CV reveals the origin of CV hysteresis to be a shift in the rate-determining step, from methanol dehydration to OH adsorption by water dissociation, induced by a change in Pt surface coverage with oxygenated species. The peak ratio between forward oxidation peak current (I-f) and backward oxidation peak current (I-b), which is I-f/I-b, is not related to the degree of CO tolerance but to the degree of oxophilicity indeed.