Synergistic coupling of defective Ru nanoclusters with oxygen-ligand-steered Ru single-atoms modifying interfacial water structure and key intermediates bonding toward efficient hydrogen energy conversion

Constructing highly efficient ruthenium (Ru)-based electrocatalysts and understanding their reaction mechanisms for hydrogen energy conversion are highly desirable, but extremely challenge. Herein, we integrate the well-dispersed defective Ru nanoclusters and oxygen-coordinated Ru single atoms into one electrocatalyst (RuSAO4/RuNC) toward alkaline hydrogen oxidation and evolution reactions (HOR/HER). Synergistic catalytic mechanism of dual-sites has been revealed by in situ ATR-SEIRAS characterization, EDTA/SCN- poisoning experiments and DFT calculations. Benefiting from the electronic redistribution between RuSA-O4 and RuNC sites, the single-atom RuSA-O4 species can act as Lewis acid sites that display strong affinity toward interfacial water via an O-down (H2O down arrow) conformation and subsequently promote water dissociation/formation as well as hydroxide adsorption. Meanwhile, adjacent defective Ru sites have around thermoneutral value of H adsorption free energy. RuNC works with RuSA-O4 species, collaboratively reducing reaction barriers. As expected, the RuSAO4/RuNC achieves 20.3 times mass activity of commercial Pt/C for alkaline HOR at 10 mV overpotential and excellent alkaline HER activity with a low overpotential of 22 mV to deliver 10 mA cm-2, as well as considerable HER mass activity of 17.0-times compared to commercial Pt/C at 50 mV overpotential. Besides, the synergistic dual-sites strategy can also be extended to prepare efficient PtSA-O4/PtNC and IrSA-O4/IrNC electrocatalysts.