An X-ray photoelectron spectroscopic study of electrocatalytic activity for chlorine evolution on amorphous palladium-phosphorus alloys containing rhodium, iridium or platinum

Abstract

The relationship between the electrocatalytic activity for chlorine evolution and the nature of the surface film formed on amorphous palladium-base alloy anodes during electrolysis of a hot concentrated sodium chloride solution was investigated. Chlorine evolution took place on the surface film in which cations were mainly those of additive group metals such as rhdoium, iridium or platinum ions. Amorphous PdIrP alloys showed a high activity for chlorine evolution, while a high rate of chlorine evolution on amorphous PdPtP alloys to produce chlorine gas at a further high rate even at very high overpotentials. This was interpreted in term of formation of a surface film of a low electronic conductivity due to an increase in concentration of a higher valency platinum ion Pt 4+ at high overpotentials. A large amount of neutral chlorine was found on the surface of the amorphous PdRhP andPdPtP alloys polarized at high overpotentials. This was assigned mainly to adsorbed molecular chlorine; that is, the final products of the chlorine evolution reaction, and the difficulty of their release seemed responsible for the difficulty in increasing the rate of chlorine evolution on the amorphous alloys containing rhodium and platinum. The amorphous PdIrP alloys were significantly active for chlorine evolution because they were able to release chlorine molecules without difficulty in addition to the fact that the relative amounts of the higher valency cations in the surface film were not appreciably changed with potential.