Co

Photocatalytic CO2 reduction coupled with H2O oxidation has been pursued extensively, albeit facing challenges in efficiency and selectivity. Herein, we develop a PdSAs+NPs/PTI catalyst by co-anchoring atomic and nanoparticulate Pd species on poly(triazine imide) crystals, which exhibits high activity, selectivity, and stability for CO2 reduction to CO using H2O as the reductant. Combined experimental and theoretical studies reveal that the dual Pd species synergistically enhance charge separation and transfer while promoting CO2 activation, CO desorption, and H2O dissociation. Photo-stimulated electrons migrate to Pd nanoparticles to reduce CO2, and holes oxidize Pd2+ sites to Pd4+ species that catalyze H2O splitting to OH* and H*. The resulting H* spills onto adjacent Pd nanoparticles to support proton-coupled CO2 reduction, whereas OH* is oxidized by Pd4+ to evolve O2, regenerating Pd2+, and closing the catalysis cycle. Importantly, the photoinduced Pd4+ sites dynamically modulate the local adsorption environment, weakening *CO binding on nearby Pd nanoparticles. This facilitates *CO desorption and hampers its hydrogenation to CH4, enabling high CO selectivity. The optimal catalyst achieves a CO yield rate of 22.2 mmol gPd -1 h-1 with 95.7% selectivity, stably operating over 30 h.