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

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, RuC-NiCoP catalyst, ruthenium clusters (RuC) immobilized onto NiCoP, is developed to elucidate the superior performance of RuC in enhancing bifunctional electrocatalytic activity over ruthenium single atoms (RuSA). The RuC-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 RuSA-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 RuC improves the adsorption energy for H2O and N2H4, optimizes the H* intermediate desorption, and reduces the dehydrogenation barrier from *N2H3 to *N2H2. Additionally, the direct hydrazine fuel cell with a RuC-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.