Mechanistic study of the hydrogen evolution reaction on Ni-Co-Zn electrodes

Electrodeposited Ni-Co-Zn alloy on the mild steel substrate has shown high electrochemical activity for the hydrogen evolution reaction. Such materials were investigated previously by EDX surface analysis and evaluated as H sub 2 -evolving cathodes in alkaline solution through steady-state techniques and under conditions of long-term operation. The material was found to have high surface area and its polarization behavior to exhibit a low Tafel slope. This paper describes a detailed mechanistic 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 suggests a mechanism involving an electron transfer followed by an electrochemical desorption step (Volmer-Heyrovsky mechanism). Through the study of the effect of temperature, it was possible to calculate the apparent activation energy of the rate determining step (25 kJ mol exp -1 ) which is the same value as that found for the overall reaction.