Synthetic tuning stabilizes a high-valence Ru single site for efficient electrolysis

Water electrolysis powered by renewable electricity can produce clean hydrogen, but the technology is limited by the slow anodic oxygen evolution reaction (OER). The most active monometallic OER catalyst is high-valence ruthenium, but it is thermodynamically unstable. Here we leverage the strong and tunable interaction between substrate and active site found in single atom catalysts, and discover a local electronic manipulation strategy for stabilizing high-valence Ru single sites (Ru SS) on a class of Ni-based phosphate porous hollow spheres (Ru SS MNiPi PHSs where M = Fe, Co, Mn, Cu) for efficient electrolysis. Both X-ray absorption fine structure and density functional theory calculation results verify the intrinsic stability of the catalyst, and suggest that this originates from the tailored valence state, coordination number and local electronic structure of the Ru SS. We formulate general guidelines for stabilizing high-valence catalytic sites and introduce a double-volcano plot to describe the superior electrocatalytic behaviours of high-valence Ru SS. The optimum Ru SS/FeNiPi achieves a low overpotential of 204 mV and 49 mV for the OER and hydrogen evolution reaction at 10 mA cm−2, respectively. Assembling Ru SS/FeNiPi in an industrial-level electrolyser with a low Ru loading of 0.081 mg cm−2 realizes a stable industrial current density of 2,000 mA cm−2 at 1.78 V, which is the highest reported value in alkaline electrolyte to the best of our knowledge, and exceeds that of commercial Pt//RuO2 by 5.7 times. Water electrolysis can produce clean hydrogen, but it is limited by the slow anodic oxygen evolution reaction. Now, a local electronic manipulation strategy for stabilizing high-valence Ru single site catalysts has been developed. The catalyst demonstrates efficient bifunctional activity for water electrolysis.