An asymmetric RE–O–Ru unit with bridged oxygen vacancies accelerates deprotonation during 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 the RuO₂ matrix by constructing an asymmetric RE–O–Ru structural unit. Taking Sm as a RE model, the incorporation of Sm into RuO₂ induces the formation of an asymmetric Sm–O–Ru unit with a unique f–p–d electron ladder and an adjacent bridged oxygen vacancy (O_v), which compensates for electron loss in Ru species and creates vacancy-localized electronic perturbation at the bridged O_v due to the delocalization of 4f electrons. The optimized Sm–RuO_2−x–O_v 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 an acidic medium, outperforming Sm-free RuO₂ and most other reported Ru-based catalysts. In situ characterization and theoretical analysis demonstrate that 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 the OER process, leading to high OER activity and stability. The potential role of asymmetric RE–O–Ru units with bridged O_v 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.