Kinetics of hydrogen evolution reaction in alkaline electrolysis on a Ni cathode in the presence of Ni–Co–Mo based ionic activators

Abstract

This paper presents investigations on the influence of in-situ ionic activation using combination of three d-metals: Ni, Co and Mo on the hydrogen evolution reaction (HER) mechanism and kinetics. Polarization measurements were performed to obtain kinetic parameters for the HER and the results are presented to show Tafel slopes, exchange current densities and apparent energy of activation. The values of the kinetic parameters confirm the existence of two Tafel slopes, in the case of NiCoMo based ionic activators (i.a.) in the investigated temperature range, with very high values of the exchange current density. Electrochemical impedance spectroscopy measurements were employed to further investigate the origin of the obtained electrocatalytic effect on the HER. The measurements were performed at several overpotentials and temperatures. It was found that co-deposition of Ni, Co and Mo species on the Ni cathode results in a large number of active sites for hydrogen adsorption, and a synergetic effect giving electronic structure suitable for the HER, are the main factors contributing to the enhanced HER kinetics. It was shown that EIS measurements had a crucial role in determining the HER mechanism, especially with the complex in-situ activation of the alkaline electrolysis.