Electronic tuning of RuO₂ polarizes metal–oxygen redox for proton exchange membrane water electrolysis

The metal–oxygen redox behavior governs the performance of transition metal oxides in many electrochemical reactions, especially for RuO2 with the activity–stability paradox in the anode oxygen evolution reaction of proton exchange membrane water electrolyzers. Herein, we modulate the electronic structure of RuO2 near the Fermi level to promote reversible Ru redox while suppressing the oxidative release of lattice oxygen. As a result, the RuO2 integrated with electron-rich p-block metals Sb achieves an overpotential of 220 mV and long-term operational stability of 1200 h at 10 mA cm−2. The assembled proton exchange membrane water electrolyzers can operate steadily over 100 h at 100, 500, and 1000 mA cm−2. Further advanced in-situ characterizations reveal the more reversible and milder Ru redox and the passivated lattice oxygen reactivity, which suppresses drastic structural changes of RuO2 during the oxygen evolution reaction. This work highlights the importance of engineering metal-oxygen redox behavior and provides insights for designing high-performance catalysts for energy conversion and storage devices.