MECHANISTIC STUDY OF THE HYDROGEN EVOLUTION REACTION ON NI-CO-ZN ELECTRODES

Electrodeposited Ni-Co-Zn alloy on a mild steel substrate have shown h igh electrochemical activity for the hydrogen evolution reaction. Such materials were investigated previously by EDX surface analysis and ev aluated as H-2-evolving cathodes in alkaline solution through steady-s tate techniques and under conditions of long-term operation. The mater ial was found to have high surface area and its polarization behaviour to exhibit a low Tafel slope. This paper describes a detailed mechani stic study of the hydrogen evolution reaction on Ni-Co-Zn carried out mainly with impedance techniques. The values of the rate constants for the elementary steps were obtained. The analysis of the results sugge sts a mechanism involving an electron transfer followed by an electroc hemical desorption step (Volmer-Heyrovsky mechanism). Through the stud y of the effect of temperature, it was possible to calculate the appar ent activation energy of the rate determining step (25 kJ mol(-1)) whi ch is the same value as that found for the overall reaction.