Entropy-Enabled Stabilization and Activity Enhancement of Ruthenium Oxides for Acidic Oxygen Evolution

Achieving both high catalytic activity and long-term electrochemical stability remains a central challenge for acidic oxygen evolution reaction (OER) catalysts. Using benchmark ruthenium oxide (RuO₂) as a model system, we employ the Pourbaix decomposition free energy (ΔG_pbx) as a quantitative stability descriptor and demonstrate that high-entropy design enables access to RuO₂-based oxides with enhanced stability. Guided by this insight, we computationally identify an idealized stoichiometric high-entropy oxide, RuMnFeNiCuO₂, with markedly reduced ΔG_pbx. Machine-learning-assisted density functional theory calculations reveal that compositional complexity modulates Ru-O bonding characteristics and diversifies the electronic structure of surface Ru sites, enabling roughly two-thirds of them to outperform those on pristine RuO₂. Proof-of-concept experiments validate these predictions using the corresponding synthesized RuMnFeNiCuO_x catalyst, where x accounts for oxygen nonstoichiometry. This catalyst exhibits an overpotential of 196 mV at 10 mA cm^-2 and only 2% activity loss after 1000 accelerated CV cycles, surpassing RuO₂ in both activity and durability. This work establishes an entropy-enabled and ΔG_pbx-guided design framework for acid-stable and high-performance OER catalysts, providing a generalizable strategy for next-generation energy conversion materials.