Dual-Descriptor-Guided Screening of Stable Metal-Doped RuO₂ Catalysts for Acidic Oxygen Evolution

Doping metallic elements into RuO₂ enhances the efficiency of proton-exchange membrane water electrolyzers (PEMWEs), yet identifying optimal dopants remains challenging due to a complex interplay of structural, electronic, and thermodynamic factors. Herein, computed E-pH-based Pourbaix diagrams combined with Ru-O bond-length analysis served as dual descriptors to evaluate the dopant-induced stability of RuO₂. First, thermodynamic preferences of various dopants were revealed by comparing the formation energies of three oxygen-coordination states on M-RuO₂ surfaces: O-covered (O_c), pristine, and O-depleted (O_d). Second, first-principles-derived Pourbaix diagrams for M-RuO₂, constructed as a function of pH from the formation energy, reflected the proton/electron transfer during oxidation and revealed metal-dependent thermodynamic stability. These diagrams defined distinct stability regions (SRs), governed by triple-point pH and phase-transition potentials (RuO₂ to Ru³⁺/RuO₄), serving as effective descriptors for dopant screening. Third, the Ru-O bond length (BL) acted as a structural descriptor, revealing that longer Ru^*O-O (Ru^*O: Ru with O adsorption) bonds suppress RuO₄ formation, while shorter Ru^Ov-O (Ru^Ov: Ru with O vacancies) bonds reduce Ru³⁺ formation. This led to a volcano-type relationship between the SR and BLs, establishing two thresholds for dopant selection. Finally, eight dopants (Rh, Zn, Ga, Bi, Mn, Nb, Sn, and Os) were identified at the volcano peak, consistent with the experiments. Together, these thermodynamic structural descriptors offer a robust, universal framework for screening stable Ru-based electrocatalysts.