Oxygen spillover from RuO₂ to MoO₃ enhances the activity and durability of RuO₂ for acidic oxygen evolution

Balancing the trade-off between the activity and durability of acidic oxygen evolution reaction (OER) catalysts is of key concern in the field of electrocatalysis. RuO₂ delivers good activity but displays poor stability due to the over-oxidation and consequent leachability of surface ruthenium species. Herein, we report an oxygen spillover strategy by designing RuO₂/MoO₃ catalysts with abundant and intimate interfaces to enable spillover of the reactive *O intermediate from RuO₂ to MoO₃ and thereby suppress over-oxidation and dissolution of RuO₂, delivering both high activity and stability of Ru-based electrocatalysts. RuO₂/MoO₃ catalysts exhibited a significantly low overpotential of 167 mV at 10 mA cm⁻² and negligible degradation of OER performance within a period of 300 h in 0.5 M H₂SO₄. Experimental evidence (in situ Raman spectra, cyclic voltammetry analysis, operando Fourier transform infrared spectroscopy, etc.), along with theoretical calculations demonstrated the occurrence of oxygen spillover from RuO₂ to MoO₃ and the subsequent participation of lattice oxygen of MoO₃ instead of RuO₂ for the steps of the release of oxygen, generation of oxygen vacancies and rehabilitation of the lattice oxygen during the acidic OER. This study provides a unique approach utilizing oxygen spillover to address the challenge associated with balancing the activity and stability of Ru-based OER electrocatalysts.