Influence of Surface Oxides on the Electrochemical Behaviour of Ni(111) in the Hydrogen Evolution Potential Region

The electrochemical behaviour of nickel (Ni) surfaces in the hydrogen evolution reaction (HER) potential region is strongly influenced by the presence of surface oxides; however, controlling and quantifying such effects remain experimentally challenging. In this study, we establish an improved electrode preparation and transfer methodology that minimises unintended surface oxidation arising from short-term air exposure, enabling systematic investigation of the intrinsic electrochemical behaviour of Ni electrodes. Using monocrystalline bead-shaped Ni electrodes and well-defined Ni(111) single-crystal electrodes in alkaline electrolyte, we examine the reversible and irreversible redox processes associated with the metallic Ni, α-hydroxide, and β-hydroxide species. Cyclic voltammetry measurements reveal that trace amounts of surface oxide formed during brief air exposure can markedly enhance the apparent HER activity, whereas suppression of oxidation leads to strongly diminished HER activity. The transformation from α-hydroxide to β-hydroxide is shown to commence once about one equivalent monolayer of α-hydroxide is formed, and proceeds irreversibly with increasing anodic excursion and repetitive potential cycling. On the Ni(111) surface, an analysis of the voltammetric features suggests that this transformation occurs preferentially at step or defect sites, while terraces remain comparatively less affected. The HER activity exhibits a non-monotonic dependence on the surface oxide accumulation, indicating the existence of an optimum amount of oxide. These results highlight the critical role of trace amounts of surface oxides in governing the HER behaviour on Ni and emphasise the necessity of precise surface-state control in electrochemical studies.