Nickel-based materials underpin alkaline water electrolysis, yet their intrinsic activity remains difficult to quantify. Reported structure–activity relationships vary widely across the literature, driven by unresolved challenges in electrochemically active surface area (ECSA) normalisation and by the dynamic redox chemistry of nickel surfaces under polarisation. Here, we present an integrated electrochemical framework that resolves these inconsistencies by explicitly linking crystallography, local surface structure, and intrinsic reactivity across multiple length scales.
We first tackle the fundamental challenge of ECSA determination for nickel, a prerequisite for meaningful comparison of intrinsic catalytic activity. A unified ECSA methodology is developed that is applicable to metallic nickel as well as nickel-derived oxides, hydroxides, and oxyhydroxides, enabling consistent normalisation of electrocatalytic currents across chemically evolving surfaces. Building on this foundation, high-resolution electrochemical mapping using scanning electrochemical cell microscopy (SECCM) is employed to directly probe the hydrogen and oxygen evolution reactions on polycrystalline nickel. These measurements reveal pronounced spatial heterogeneity in activity that apparently correlates with crystallographic orientation and local surface structure, demonstrating that macroscopic measurements obscure critical structure-sensitive behaviour.
To move beyond polycrystalline complexity, we investigate well-defined single-crystalline nickel oxide particles exposing distinct facets. This approach enables direct identification of facet-dependent electrocatalytic behaviour under alkaline conditions and provides insights into the origins of activity variations. Collectively, these results reconcile discrepancies in the nickel literature and highlight how surface structure, rather than composition alone, governs catalytic performance.
By integrating quantitative surface area determination with spatially and crystallographically resolved electrochemistry, this work provides a general framework for evaluating intrinsic electrocatalytic activity and offers practical guidance for the rational design and benchmarking of next-generation energy materials for alkaline electrolysis.