The oxygen evolution reaction on passive oxide covered transition metal electrodes in aqueous alkaline solution. Part 1 - Nickel

Abstract

Various aspects of the oxygen evolution reaction (OER) at passive oxide covered polycrystalline Ni electrodes in aqueous alkaline solution were investigated using electrochemical techniques. Steady state polarisation and electrochemical impedance spectroscopy (EIS) were used to measure kinetically significant parameters including the Tafel slope and the reaction order with respect to OH- activity. While reproducible values of the Tafel slope were readily observed, the recorded current density at a given applied potential displayed considerable variability over the course of a number of polarisation experiments, rendering difficult the extraction of the experimental reaction order parameter. This problem was resolved by applying relatively mild electrochemical pre-treatment routines to the working electrode. Cyclic voltammetry was used to probe the important issue of the interplay between the nickel oxy-hydroxide surface electrochemistry and the activity of the electrode for the OER. A current transient decay method was employed to estimate the electrode roughness factor. Amongst the mechanistic pathways proposed for the OER in the literature, only two are consistent with the experimental results reported here. The relative merits of these two pathways are discussed and the most likely is identified. The well known Krasil’shchikov mechanism is not suggested.