Structural equilibrium in indium oxide enables high-performance electrocatalytic hydrogen peroxide synthesis

The electrochemical two-electron oxygen reduction reaction (2e^- ORR) offers a sustainable route to hydrogen peroxide, yet it requires catalysts that combine high electrical conductivity with well-designed surface sites for optimal *OOH intermediate binding. Conventional thermal annealing often improves conductivity but at the expense of catalytically essential defects. Here, using a carbon-supported In₂O₃ system, we demonstrate that precise annealing conditions can simultaneously tailor the catalyst's conductive network and its surface-active sites. The integrated carbon support significantly elevates and stabilizes the overall electrode conductivity, while controlled annealing tunes the oxide's crystallinity, oxygen vacancy concentration, and Lewis-acidic In sites. This optimally balanced In₂O₃ catalyst exhibits optimized *OOH binding, achieving ∼90% H₂O₂ selectivity, a production rate of 44.7 ± 3.0 mol g_cat^-1 h^-1 at 250 mA cm^-2 in a flow cell while maintaining >85% Faradaic efficiency, and robust operation stability. This work establishes a principle of structural equilibration that shifts the catalyst design paradigm from a trade-off to a synergy, providing a generalizable strategy for engineering high-performance oxide electrocatalysts.