ELECTROCATALYSIS OF ORGANIC OXIDATIONS - INFLUENCE OF WATER-ADSORPTION ON THE RATE OF REACTION

Current/potential responses of small organic molecules show as a chara cteristic feature an increase in anodic current when changing the pote ntial in the cathodic direction. In situ infrared data on the adsorpti on of methanal, formic acid, and water at Pt(111) are used to develop a new model explaining these well-known catalytic effects. Since the s trength of water adsorption increases with increasing potentials above 0.4 V, the adsorption of organic molecules has to be considered as a water displacement reaction. The reaction rate is thus the result elf the concurrence of two processes that are oppositely affected by the p otential: the rate of oxidation (charge transfer) and the rate of adso rption. In situ TX data and cyclic voltammograms for the oxidation of methanal and formic acid on a Pt(111) surface are presented and discus sed. For comparison, data on CO oxidation are presented.