CO₂ Photoreduction by H₂O: Cooperative Catalysis of Palladium Species on Poly(triazine imide) Crystals

Photocatalytic CO 2 reduction coupled with H 2 O oxidation has been pursued extensively, albeit facing challenges in efficiency and selectivity. Herein, we develop a Pd SAs+NPs /PTI catalyst by co‐anchoring atomic and nanoparticulate Pd species on poly(triazine imide) crystals, which exhibits high activity, selectivity, and stability for CO 2 reduction to CO using H 2 O as the reductant. Combined experimental and theoretical studies reveal that the dual Pd species synergistically enhance charge separation and transfer while promoting CO 2 activation, CO desorption, and H 2 O dissociation. Photo‐stimulated electrons migrate to Pd nanoparticles to reduce CO 2 , and holes oxidize Pd 2+ sites to Pd 4+ species that catalyze H 2 O splitting to OH* and H*. The resulting H* spills onto adjacent Pd nanoparticles to support proton‐coupled CO 2 reduction, whereas OH* is oxidized by Pd 4+ to evolve O 2 , regenerating Pd 2+ , and closing the catalysis cycle. Importantly, the photoinduced Pd 4+ sites dynamically modulate the local adsorption environment, weakening *CO binding on nearby Pd nanoparticles. This facilitates *CO desorption and hampers its hydrogenation to CH 4 , enabling high CO selectivity. The optimal catalyst achieves a CO yield rate of 22.2 mmol g Pd −1 h −1 with 95.7% selectivity, stably operating over 30 h.