Kinetics and mechanism of hydrogen evolution reaction on cobalt silicides in alkaline solutions

Abstract

Cathodic polarisation curves and impedance spectra for cobalt silicides Co2Si and CoSi2 in 0.5–2M KOH at ambient temperature were obtained. It was shown that electrocatalytic activity of both silicides in hydrogen evolution reaction (HER) is higher than that of cobalt. The dependences of equivalent circuit elements on the electrode potential were analysed. The conclusion was made that the atomic hydrogen adsorption on the surface of cobalt silicides is described by the Langmuir isotherm, and hydrogen evolution proceeds through the Volmer–Heyrovsky mechanism (at α1≠α2 for Co2Si and α1=α2 for CoSi2; α1 and α2 are the transfer coefficients for the Volmer and Heyrovsky steps respectively). The Heyrovsky reaction is probably the rate-determining step. The values of the kinetic parameters of HER on Co2Si and CoSi2 in 1M KOH were estimated.