Tailoring High‐Entropy Oxide via Grain Boundary Engineering to Establish Adjacent Asymmetric Redox Sites for Full‐Spectrum Photothermal Catalytic CO ₂ Reduction

Photothermal catalytic CO₂ reduction offers a promising route for full-spectrum carbon recycling. While high-entropy oxides (HEO) show potential as photothermal catalysts, their efficiency is often limited by uncoordinated kinetics in CO₂ activation, active proton formation via H₂O dissociation, and proton migration. Herein, a grain boundaries (GB) engineering strategy is reported to tailor HEO, constructing adjacent asymmetric redox dual sites that simultaneously promote CO₂ activation and proton feeding. Using (CoCrFeMnNi)₃O₄ HEO nanosheets, it is found that a high density of GB induces electronic redistribution and promotes asymmetric oxygen vacancies (Vo) formation, creating abundant polarized Fe-Vo-Cr-O motifs. Specifically, electron-deficient Fe centers function as Lewis acid sites, accelerating H₂O activation to yield active proton, while adjacent photogenerated electron-rich Cr─O clusters primarily adsorb CO₂ via a bridging mode. Furthermore, the photothermal effect of (CoCrFeMnNi)₃O₄ HEO catalysts leads to a substantial elevation of the catalyst surface temperature, reaching ≈198 °C, synergistically optimizes the thermodynamics and kinetics of the proton-coupled electron transfer process. Consequently, the GB-rich HEO catalysts achieve impressive CH₄ and CO yield rates of 677.7 and 957.2 µmol g^-1 h^-1, respectively, with a notable apparent quantum yield of 0.38% at 420 nm, highlighting their significant advantage in CO₂ photoreduction.