Constructing Fully‐Active and Ultra‐Active Sites in High‐Entropy Alloy Nanoclusters for Hydrazine Oxidation‐Assisted Electrolytic Hydrogen Production

Abstract The development of sufficiently high‐efficiency systems and effective catalysts for electrocatalytic hydrogen production is of great significance but challenging. Here, high‐entropy alloy nanoclusters (HEANCs) with full‐active sites and super‐active sites are innovatively constructed for hydrazine oxidation‐assisted electrolytic hydrogen production. The HEANCs show an average size of only seven atomic layers (1.48 nm). As the catalysts for both hydrogen evolution reaction (HER) and hydrazine oxidation reaction, the HEANC/C exhibits the best‐level performance among reported electrocatalysts. Especially, the HEANC/C achieves an ultrahigh mass activity of 12.85 A mg⁻¹_{noble metals} at −0.07 V and overpotential of only 9.5 mV for 10 mA cm⁻² for alkaline HER. Further, with HEANC/C as both anode and cathode catalysts, an overall hydrazine oxidation‐assisted splitting (OHzS) electrolyzer shows a record mass activity of 250.2 mA mg⁻¹_catalysts at 0.1 V and only requires working voltages of 0.025 and 0.181 V to reach 10 and 100 mA cm⁻², respectively, outperforming those of overall water‐splitting system and other reported chemicals‐assisted hydrogen production systems. Active site libraries including 72 sites on HEANC surface are originally constructed by theoretical calculations, revealing that all sites on HEANC surface are effective active sites for OHzS; especially some are super‐active sites, endowing the best‐level performance of HEANC/C.