An X-ray photoelectron spectroscopic study of electrocatalytic activity of platinum group metals for chlorine evolution

Abstract

A correlation of the catalytic activity for anodic chlorine evolution of platinum group metals to the nature of the surface film formed during chlorine evolution in a sodium chloride solution was studied by X-ray photoelectron spectroscopy. The change in the surface film with increasing potential was found on platinum, including an increase in the cationic valence. This seemed responsible for the decrease in the activity for chlorine evolution on platinum in the high potential region. Increasing potential did not result in the appreciable increase in the cationic valence in the surface film on the other platinum group metals. Replacement of hydroxyl ions in the surface film by chloride ions became easier in the order of rhodium, iridium and palladium, and the activity for anodic chlorine evolution increased in this order due possibly to an increase in the amount of chloride ions in the film which seemed to be one of the reactants in the rate determining electrochemical desorption of adsorbed chlorine atom. Chlorine molecules adsorbed on the surface film were also found. It was assumed that the activity for anodic chlorine evolution might be low when the metal surface was covered by a large amount of molecular chlorine which was the reaction product.