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.