Fig. 1: Mechanistic prediction of intermediates on the catalyst surface.

a Simulative structural model of symmetric dual active sites. b The illustration of the end-on model and bridge model. c Schematic structure models of Ru(SA)-NiOMS, Ru(SA)-OMS, NiOMS, and OMS from the top view. Surface Pourbaix diagrams of d Ru(SA)-NiOMS, e Ru(SA)-OMS, f NiOMS, and g OMS. The thermodynamically stable states of the surface under relevant reversible hydrogen electrode (RHE) and pH values are highlighted by green (for O*), blue (for OH*), and orange (for H2O*), respectively. h Computed H2O*, OH*, and O* adsorption free energies on catalyst surfaces. i Energy levels of theoretical redox potential (UR) and theoretical coupling potential (UL). The UR is defined as the electrode potential of H2O* deprotonation, and the UL is defined as the limiting electrode potential needed to remove the surface OH* species for the theoretical formation of intramolecular O–O bonds.