On the effect of temperature and surface oxidation on the kinetics of hydrogen electrode reactions on nickel in alkaline media

The influence of the temperature on the kinetics of the hydrogen oxidation (HOR) and evolution reactions (HER) on Ni electrodes has been explored in the range from 298 to 338 K. By combining an expexrimental cyclic voltammetry study and microkinetic modeling, the rate constants and the activation energies of the individual Volmer-Tafel-Heyrovsky steps have been extracted for two surface states of Ni electrode, namely metallic Ni and partially oxidized one. The kinetic model suggests that the HOR/HER on metallic Ni follows the Heyrovsky-Volmer mechanism characterized by strong adsorption of the hydrogen intermediate and low reaction rate. Partial coverage of the electrode surface with Ni oxide species results in a decrease of the strength of adsorption of hydrogen atoms and an increase of the rate of the Volmer step thus leading to a significant enhancement of the HOR/HER kinetics. Furthermore, the kinetic model provides evidence for a contribution of the Tafel step in the reaction mechanism for a partially oxidized electrode. The apparent activation energy is shown to be slightly dependent on the surface state, decreasing from 30 +/- 1 for metallic to 26 +/- 1 kJ mol(-1) for partially oxidized Ni. (C) 2018 Elsevier Ltd. All rights reserved.