Asymmetric RE-O-Ru unit with bridged oxygen vacancies accelerates deprotonation of acidic water oxidation

Abstract

Proton exchange membrane water electrolysis (PEMWE) is a promising technology for sustainable hydrogen production; however, the slow deprotonation of oxo-intermediates on RuO2 during the acidic oxygen evolution reaction (OER) limits its long-term stability. Herein, we propose an innovative and effective rare-earth (RE)-mediated strategy to accelerate the deprotonation of OER intermediates on RuO₂ matrix by constructing asymmetric RE-O-Ru structural unit. Taking Sm as a RE model, the incorporation of Sm into RuO2 induces the formation of asymmetric Sm-O-Ru unit with a unique f-p-d electron ladder and an adjacent bridged oxygen vacancy (Ov), which compensates for electron loss in Ru species and creates vacancy-localized electronic perturbation at the bridged Ov due to the delocalization of 4f electrons. The optimized Sm-RuO2-x-Ov catalyst requires an overpotential of only 217 mV at 10 mA cm-2 and operates steadily for over 300 h with a negligible degradation rate of ~27 μV h-1 in acid medium, outperforming Sm-free RuO2 and most other reported Ru-based catalysts. In situ characterization and theoretical analysis demonstrate the constructed asymmetric Sm-O-Ru unit prevents the over-oxidation of Ru species at high voltages and accelerates the *OH deprotonation at the surface oxygen vacancy during OER process, leading to high OER activity and stability. The potential role of asymmetric RE-O-Ru units with bridged Ov is also observed in other RE-doped RuO2 systems (e.g., Nd and Lu), where all catalysts exhibit enhanced deprotonation of oxygenated intermediates. We believe that the RE-mediated strategy presented in this work provides a new pathway for designing highly active and stable noble-metal-based catalysts for acidic water oxidation.