On the kinetics of the hydrogen evolution reaction on zinc in sulfate solutions

Abstract

The kinetics and mechanism of the hydrogen evolution reaction (her) were studied on zinc in 1.0 mol dm-3 Na2SO4 at 298 K, in the pH range 4.4 - 10. It was found that a combination of classical potentiostatic steady-state voltammetry (PSV) and electrochemical impedance spectroscopy (EIS) can help to elucidate dilemmas concerning the mechanism of this reaction. Thus, over the whole potential region, the reaction path of the her on zinc cannot be presented by the classical Volmer-Tafel-Heyrovsky route. It was found that the very complex S-shape of the polarization curves could be explained by two parallel reaction mechanisms for the her. The first reaction mechanism is a consecutive combination of three steps, in which the surface zinc oxide plays an active role in the her, and second reaction mechanism is a consecutive combination of a Volmer step, followed by a Heyrovsky step. The second mechanism is dominant in the more negative potential region where the active sites for the her are metallic zinc.