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

Cathodic polarisation curves and impedance spectra for cobalt silicides Co₂Si and CoSi₂ in 0.5–2 M 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 1 M KOH were estimated