Each performs its own functions: Nickel oxide supported ruthenium single-atoms and nanoclusters relay catalysis with multi-active sites for efficient alkaline hydrogen evolution reaction

Single-atom catalysts (SACs) have received enormous attention owing to their unique catalytic properties. However, designing SACs for complex reactions with several elementary reactions remains challenging because they commonly accelerate only one step of reactions. Here, the nickel oxide supported ruthenium single-atoms and nanoclusters catalyst (RuSA+NC/NiO-NF) is reported for the typical multi-step alkaline hydrogen evolution reaction. By altering the ratio of single-atoms/nanoclusters, the synergistic effect between Ru single-atoms and nanoclusters is amplified. The in-situ Raman combined with density functional theory reveals that Ru single-atoms sites display high efficiency on H2O-adsorption and dissociation, while Ru nanoclusters and NiO sites promote the H-recombination. As a consequence, the prepared RuSA+NC/NiO-NF catalyst achieves a low overpotential of 11 mV at a current density of 10 mA cm−2 together with a small Tafel slope of 29 mV decade−1. This work offers prospects for the designing of single-atom-based catalysts for multi-step reactions.