Interfacial Osmium Nanoclusters on Molybdenum Boride Enable Reverse Hydrogen Spillover for Enhanced Hydrogen Evolution

ABSTRACT The advancement of highly efficient, durable, and economically viable electrocatalysts for the hydrogen evolution reaction (HER) plays a crucial role in enabling large‐scale green hydrogen production. However, significant challenges remain in improving the efficiency of conventional catalytic processes. Here, we report osmium nanocluster‐decorated molybdenum boride (Os/MoB) as an efficient catalyst for the HER, operating via a novel hydrogen spillover mechanism. The Os/MoB catalyst achieves remarkably low overpotentials (η ₁₀ = 22, 27, and 11 mV) to reach 10 mA cm ⁻² in alkaline, acidic, and alkaline seawater (1 m KOH + seawater) electrolytes, performance that matches or surpasses commercial Pt/C. Density functional theory (DFT) calculations reveal that H ₂ O adsorbs on the MoB surface, followed by the dissociation of H ₂ O, where the generated H* species spillover to the interfacial Os sites, subsequently recombining and releasing H ₂ . Furthermore, an Os/MoB‐based anion exchange membrane water electrolyzer (AEMWE) delivers a current density of 500 mA cm ⁻² at low voltages of only 1.78 V in 1 m KOH and 1.88 V in alkaline seawater and maintains stable operation for over 100 h.