Antibonding–Vacancy Coupling Boosts Hydrogen Evolution Rate in Diborides

A non-noble-metal electrocatalyst, V1–xMox–δB2 (x = 0–1; δ < 0.2), is introduced to replace costly hydrogen evolution reaction (HER) catalysts, enabling a greener energy economy. This solid solution catalyst includes vacancy-free and Mo-vacancy-containing variants (δmax = 0.16 for x = 0.7). Combining dual active sites and vacancies, it achieves a low overpotential (η1000 = 0.391 V), outperforming Pt/C (η1000 = 0.837 V) at industry-relevant current densities. DFT calculations reveal that strong antibonding metal–boron interactions at the Fermi level in Mo-deficient samples drive a unique volcano-like behavior in the c-lattice parameter and enhance HER activity. The catalyst also demonstrates exceptional stability, showing no degradation after 24 h at 900 mA/cm2 or after 5000 CV cycles. This work highlights a novel approach to designing high-current-density non-noble-metal HER catalysts by leveraging antibonding interactions and vacancy formation.