Supra‐Photothermal CO₂ Methanation over Greenhouse‐Like Plasmonic Superstructures of Ultrasmall Cobalt Nanoparticles

Abstract Improving the solar‐to‐thermal energy conversion efficiency of photothermal nanomaterials at no expense of other physicochemical properties, e.g., the catalytic reactivity of metal nanoparticles, is highly desired for diverse applications but remains a big challenge. Herein, a synergistic strategy is developed for enhanced photothermal conversion by a greenhouse‐like plasmonic superstructure of 4 nm cobalt nanoparticles while maintaining their intrinsic catalytic reactivity. The silica shell plays a key role in retaining the plasmonic superstructures for efficient use of the full solar spectrum, and reducing the heat loss of cobalt nanoparticles via the nano‐greenhouse effect. The optimized plasmonic superstructure catalyst exhibits supra‐photothermal CO₂ methanation performance with a record‐high rate of 2.3 mol g_Co⁻¹ h⁻¹, close to 100% CH₄ selectivity, and desirable catalytic stability. This work reveals the great potential of nanoscale greenhouse effect in enhancing photothermal conversions through the combination with conventional promoting strategies, shedding light on the design of efficient photothermal nanomaterials for demanding applications.