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

Abstract Photothermal catalytic CO ₂ 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 CO ₂ activation, active proton formation via H ₂ O 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 CO ₂ activation and proton feeding. Using (CoCrFeMnNi) ₃ O ₄ 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 H ₂ O activation to yield active proton, while adjacent photogenerated electron‐rich Cr─O clusters primarily adsorb CO ₂ via a bridging mode. Furthermore, the photothermal effect of (CoCrFeMnNi) ₃ O ₄ 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 CH ₄ 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 CO ₂ photoreduction.