Breaking Base Dependence: Solar-Boosted CO ₂ Hydrogenation to Formic Acid over Confined PdAg@NH ₂ -UiO-66

The hydrogenation of carbon dioxide (CO 2 ) to formic acid under mild conditions and in the absence of alkali remains a critical challenge. Herein, we demonstrate a breakthrough in base-free CO 2 hydrogenation by confining bimetallic PdAg nanoparticles within amino-functionalized UiO-66 (PdAg@NH 2 -UiO-66), creating a light-responsive microenvironment that synergistically enhances formic acid production under mild conditions. PdAg NPs were encapsulated into NH 2 -UiO-66 via impregnation–reduction, and the catalytic performance was evaluated in a photothermal reactor (60 °C, 1 MPa, CO 2:H 2 = 1:1, H 2 O solvent) under full-spectrum light irradiation, with mechanistic insights validated by in situ DRIFTS, DFT calculations, and photoelectrochemical analysis. The catalyst achieved a record formic acid production rate of 1853 μmol g –1 h –1 (>99% selectivity) under light, 1.3 times higher than dark conditions (1440 μmol g –1 h –1 ). Light excitation drives photogenerated electrons from NH 2 -UiO-66 to the CO 2 antibonding orbital, reducing the activation barrier for *COOH formation (rate-determining step) while PdAg NPs facilitate H 2 dissociation. Confinement within NH 2 -UiO-66 enables three critical synergies: (i) atomic proximity of CO 2 activation sites (Zr-oxo clusters) and H 2 dissociation sites (PdAg NPs), (ii) localized surface plasmon resonance (LSPR) enhancing electron transfer, and (iii) photothermal effects lowering energy requirements. Therefore, this work establishes a new benchmark for solar-assisted thermocatalysis, enabling efficient CO 2 -to-fuel conversion without alkaline additives, paving the way for sustainable chemical synthesis using renewable energy.