Charge symmetry breaking stabilizes high-valence Ru sites for proton exchange membrane electrolysis

High-valence Run+ (n > 4) sites possess high catalytic activity to negotiate the sluggish oxygen evolution reaction in proton exchange membrane water electrolysis, but undergo thermodynamic instability. The synthesis of Ru-based catalysts with stable high-valence Ru sites remains challenging. Here, we present an interstitial nitrogen doping strategy to trigger a charge symmetry breaking for the stabilization of high-valence Ru sites in ruthenium dioxide. The resultant catalyst requires a low overpotential of 195 mV at 10 mA cm-2 and operates stably with negligible activity drop over 1000 hours. In-depth electrochemical characterizations combined with in-situ spectroscopic studies reveal that the presence of high-valence Ru sites accelerates the charge accumulation for the chemical bond making/breaking and water dissociation at the reaction interface, leading to enhanced kinetics. Additionally, the strong Ru-N electronic coupling and weak Ru-O covalency suppress the Ru oxidative dissolution and lattice oxygen oxidation, accounting for the long-term stability. A realistic water electrolysis cell assembled with this catalyst at the anode achieves 1000 mA cm-2 at 1.79 volts and can run steadily for at least 300 hours. Stabilizing high-valence ruthenium sites is key for efficient acidic water splitting but remains challenging. Here, the authors report an interstitial nitrogen doping strategy to stabilize these sites in ruthenium dioxide, achieving enhanced activity and long-term stability for hydrogen production.