Adsorption and anodic oxidation of methanol on iridium and rhodium electrodes

Adsorption and electro-oxidation of methanol on smooth iridium and rhodium electrodes have been studied. The regularities obtained were compared with the results of previous measurements on smooth platinum. The adsorption of methanol on iridium has been established as characterized by regularities peculiar to a surface with an exponentially distributed inhomogenity of adsorption sites (Freundlich isotherm, linear change of the activation energy of adsorption with logarithm of surface coverage). The adsorption regularities for rhodium are more complex. The character of the isotherms on iridium and rhodium, as well as on platinum, does not depend on the nature of adsorbed neutral particles (methanol, hydrogen etc) and is apparently determined by the electrode surface properties. As follows from kinetic regularities (influence of potential, concentration and pH of solution, surface coverage) the rate-determining step of steady-state methanol electro-oxidation on iridium and rhodium is the oxidation of carbonaceous chemisorbed particles by adsorbed OH radicals.