Non‐Metal Heteroatom‐Mediated Synchronous Size and Electronic Structure Control of Ru Nanoclusters for Enhanced Hydrazine Oxidation and Hydrogen Evolution Reactions

Abstract Simultaneous control over the size and electronic structure of ruthenium nanoclusters (Ru NCs) is crucial for optimizing their electrocatalytic performance. Herein, this challenge is addressed by systematically screening typical non‐metal heteroatoms (e.g., N, P, S, or B) in graphene (G) substrate to mediate the nucleation and growth of Ru NCs. Theoretical analysis identifies S as the optimal candidate mainly by comparing the Gibbs free energy of Ru adsorption. Experimentally, Ru NCs on S‐doped G (G‐S) exhibit a uniform and dense distribution, with an average diameter of ≈1.1 nm, significantly smaller than those supported on N‐, P‐, or B‐doped G. The resulting Ru/G‐S catalyst demonstrates exceptional bifunctional catalytic activity, surpassing commercial Pt/C in both the hydrazine oxidation reaction (HzOR) and hydrogen evolution reaction (HER). Specifically, it requires an ultralow working potential of −46 mV (vs RHE) for HzOR and a minimal HER overpotential of 15 mV at 10 mA cm ⁻² . In a two‐electrode system, it needs only 31 mV to deliver 10 mA cm ⁻² and maintains stability over 120 h. Mechanistic studies further reveal that S‐doping not only dictates Ru nucleation but also induces charge redistribution, lowering kinetic barriers for the formation of key HzOR and HER intermediates.