Chromium Cation‐Induced Self‐Reconstruction of a Stable and High Performance Boride‐derived Electrocatalyst for Oxygen Evolution Reaction

The rational design of efficient electrocatalysts for the oxygen evolution reaction (OER), holds the key to advancing the overall electrolytic water splitting performance. Here, a scalable one-pot synthesis of a stable chromium─iron nickel boride (Cr─FeNiB) electrocatalyst is reported for OER in which nickel-boron sites are micro-environmentally modified through interactions with iron and chromium. Comprehensive, correlative electrochemical, structural, and chemical analyses reveal the formation of amorphous-crystalline core-shell structures that transform into nanosheets upon activation with enhanced water oxidation catalytic activity. The enhanced catalytic performance is attributed to the chromium-induced chemical self-reconstruction of the catalyst, which facilitates favorable OER kinetics, increased turnover frequency, and a synergistic effect between metal and boron constituents. Density Functional Theory (DFT) calculation showed that chromium incorporation effectively shifts the d-band centers (ɛ_d) closer to the Fermi level and narrows the metal-d/boron-p band center gap (Δɛ_d-p) (Ni₂B 1.10 eV → FeNiB 0.71 eV → Cr─FeNiB 0.55 eV) ultimately enhancing OER activity. Accordingly, the Δɛ_d-p is established as a key electronic descriptor for predicting and optimizing OER performance. These findings pave the way for a better understanding of metal boride-derived electrocatalysts and also contribute to the development of efficient, stable, earth-abundant, non-noble metal catalysts for water oxidation.