A Crystallographic Descriptor for Alkaline Hydrogen Evolution on Nickel

Abstract

Crystallographic descriptors for alkaline hydrogen evolution on nickel, which are essential for the rational design of improved electrocatalysts, remain elusive, particularly for technologically relevant polycrystalline materials. Here, scanning electrochemical cell microscopy (SECCM) is combined with co-located electron backscatter diffraction (EBSD) to map grain-resolved hydrogen evolution reaction (HER) activity on polycrystalline Ni, generating a pseudo-single-crystal dataset spanning 52 individual grains. Spatially resolved voltammetry reveals pronounced orientation-dependent variability, with currents closely following the underlying microstructure. Normalization using the Ni(0) → α-Ni(OH)2 oxidation charge reduces, but does not eliminate, this heterogeneity, demonstrating that alkaline HER on Ni is intrinsically structure-sensitive. The oxidation charge itself exhibits strong orientation dependence, reflecting both the electrochemically participating surface and the propensity for hydroxide adsorption. After normalization, {001}-type orientations exhibit the highest intrinsic activity, {111}-type orientations intermediate behavior, and {101}-type orientations the lowest. Beyond discrete facet classification, the minimum angular deviation from the {101} pole (δ{101}) emerges as the statistically strongest crystallographic descriptor of intrinsic HER activity, indicating that surfaces approaching {101} are intrinsically less capable of mediating water dissociation and hydroxide adsorption. These findings establish crystallographic geometry and electrochemical surface state as independent determinants of HER kinetics and identify suppression of {101}-type orientations as a practical microstructural design strategy for high-performance Ni-based cathodes for alkaline water electrolysis.