The electrolyte effects on the kinetics of hydrogen and oxygen evolution reaction on polycrystalline nickel in alkaline media

Abstract

Understanding and controlling electrolyte effects is essential for improving the efficiency and reliability of alkaline water electrolysis. In this study, we systematically investigate the influence of alkali cation identity (Li⁺, Na⁺, K⁺) and concentration, as well as surface oxidation, on the kinetics of hydrogen and oxygen evolution reactions (HER and OER) on polycrystalline nickel. HER performance was found to be optimal in 0.1 mol dm⁻³ NaOH, while OER activity improved with increasing KOH concentration (1.0 mol dm⁻³ vs. 0.1 mol dm⁻³). In contrast, lithium-containing electrolytes consistently suppressed both reactions, likely due to the strong hydration of cations hindering interfacial charge transfer. Controlled anodic oxidation enhanced HER through the formation of β-Ni(OH)<inf>2</inf> and Ni|Ni(OH)<inf>2</inf> interfaces. In contrast, more extensive oxidation leading to NiOOH formation suppressed HER but had a more nuanced impact on OER. These results reveal a strong interplay between surface chemistry and electrolyte composition, with significant implications for both fundamental mechanistic understanding and practical catalyst optimization. The findings also highlight the importance of carefully defining electrolyte identity and electrode pre-treatment when benchmarking HER activity on nickel-based materials.