Carbon-Caged-Yttria Catalysts for Stable Electrosynthesis of H₂O₂ in Concentrated Acid

The electrosynthesis of hydrogen peroxide (H₂O₂), with renewable electricity, air, and water as inputs, offers a sustainable alternative to the conventional anthraquinone process. Performing H₂O₂ electrosynthesis in concentrated acid offers advantages in functionality and energy efficiency over alkaline media yet is currently limited by short longevity. Here, we first investigate the origins of performance loss of oxidized carbon, a proven catalyst for H₂O₂ electrosynthesis, and observe its gradual reduction to pristine carbon during acidic electrolysis. This inspires us to design a catalyst that can stabilize the oxidized carbon sites via strong Y-O-C coordination─a strategy we instantiate via carbon-caged-yttria (C@Y₂O_x) catalysts. In acids, the C@Y₂O_x catalyst sustains a H₂O₂ selectivity of 97% after 10,000 cycles. Integrated into a gas diffusion electrode and operated in concentrated acids of pH < 0, the C@Y₂O_x catalyst delivers a partial current density of ∼100 mA cm^-2 at -0.4 V versus RHE over 100 h in a flow cell. Using quasi in situ NAP-XPS, operando FT-IR, and theoretical calculations, we elucidate that coordination with yttrium energetically suppresses the breakage of the O-C bond and accordingly preserves the oxidized carbon sites for selective and long-term electrosynthesis of H₂O₂.