Atomic Cluster Outperforms Single Atom in Hydrogen Evolution and Hydrazine Oxidation for Energy‐Efficient Water Splitting

Abstract The hydrazine‐assisted water splitting (HzAWS) is promising for energy‐saving hydrogen production. However, developing efficient bifunctional catalysts that exert hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR) at industrial‐grade current densities remains challenging. Here, Ru C ‐NiCoP catalyst, ruthenium clusters (Ru C ) immobilized onto NiCoP, is developed to elucidate the superior performance of Ru C in enhancing bifunctional electrocatalytic activity over ruthenium single atoms (Ru SA ). The Ru C ‐NiCoP achieves current densities of 10 and 100 mA cm −2 for HER and HzOR with working potentials of −10 and −89 mV, respectively, outperforming Ru SA ‐NiCoP (−16 and −65 mV). During HzAWS, a cell voltage reduction of 1.77 V at 300 mA cm −2 is observed compared to overall water splitting. Density functional theory calculations reveal that Ru C improves the adsorption energy for H 2 O and N 2 H 4 , optimizes the H* intermediate desorption, and reduces the dehydrogenation barrier from *N 2 H 3 to *N 2 H 2 . Additionally, the direct hydrazine fuel cell with a Ru C ‐NiCoP anode delivers an impressive power density of 226 mW cm −2 and enables a self‐powered hydrogen production system, achieving an unprecedented hydrogen production rate of 4.9 mmol cm −2 h −1 . This work offers a new perspective on developing efficient sub‐nanoscale bifunctional electrocatalysts and advancing practical energy‐saving hydrogen production techniques.