Influence of the NaOH Concentration on the Hydrogen Electrode Reaction Kinetics of Ni and NiCu Electrodes

Abstract Nickel is a promising electrocatalyst for hydrogen electrode reactions in alkaline media. Its electrocatalytic activity for hydrogen oxidation and evolution reactions can be enhanced when its surface is partially covered by Ni (hydr)oxides or by associating it with Cu. In this work, the influence of the NaOH concentration on the hydrogen electrode kinetics on various Ni electrodes is investigated. On metallic Ni, the electrocatalytic activity (measured as an exchange current density normalized to the surface area of Ni) is almost constant between pH 12 and 14, whereas it decreases by a factor of two on partially oxidized Ni and on the NiCu/C electrode. Analyzing the current potential curves with the help of microkinetic modeling reveals that the H ad and OH ad binding energies on Ni do not depend on pH, whereas the rate constants of the Volmer and Heyrovsky reactions decrease with pH. The pH effect on the electron transfer elementary act is briefly discussed in the framework of a quantum mechanical theory.