Solar‐Driven CO ₂ and H ₂ O Conversion Over a High‐Density Nickel Single‐Site Catalyst With Unprecedented CO Evolution Rate

Achieving carbon dioxide (CO 2 ) reduction with water (H 2 O) on photothermal catalysts remains a major challenge. Here, we report a high‐density Ni single‐site catalyst based on a porous aromatic framework (PAF), which enables efficient CO 2 reduction in pure H 2 O under full‐spectrum illumination without the need for additives. Ni‐PAF achieves CO production rates of 25.64 mmol·g −1 ·h −1 under Xe light and 229.04 mmol·g −1 ·h −1 under concentrated sunlight, exceeding all reported results. Nitrogen‐rich groups anchor Ni single sites uniformly, serving as the active centers for the activation of CO 2 and H 2 O. Calculations and experiments show that UV–Vis light drives charge transfer, while IR absorption induces a localized temperature rise. Besides, the low thermal conductivity of PAF confines this heat, creating a thermal microenvironment that enhances charge migration and proton transfer, thereby accelerating CO 2 conversion. These synergistic effects make Ni‐PAF a highly promising catalyst for solar‐driven CO 2 reduction in H 2 O and offer new opportunities for designing efficient photothermal catalysts toward solar fuel production.