Engineering spatially proximate redox sites in Pd-In/TiO₂ photocatalyst for selective CO₂ photoreduction

The synergistic integration of redox reactions in the photocatalyst poses a significant challenge for CO₂ photoreduction. Addressing this issue requires the design of spatially proximate redox sites while effectively suppressing charge recombination at these sites. This work offers a pioneering tactic that exploits synergistic redox reactions in close atomic proximity. The deliberate incorporation of palladium and indium into TiO₂, where the Pd site assists in hole accumulation, accelerates water dissociation, and generates highly active H* species. Meanwhile, adjacent In sites capture photogenerated electrons from TiO₂, producing reactive intermediates by activating CO₂. The synergistic incorporation of Pd and In accelerates redox functionality, boosts charge carrier separation, and mitigates recombination at closely situated redox sites. Comprehensive characterizations, including in-situ XPS and FTIR, strengthen these innovative outcomes. The optimized Pd_0.5-In₁/TiO₂ photocatalyst achieves nearly 100 % selectivity of CH₄ with a production rate of 30.5 µmol g^-1h⁻¹ without the use of any sacrificial reagent, demonstrating a 25-fold improvement compared to pristine TiO₂. In-situ infrared spectroscopy further validates that the synergistic doping of metal ions promotes the formation of *CH₃O and *CHO, key intermediates in the production of CH₄. This investigation provides valuable insight into the intricate design of coupled redox active sites.