Unravelling the effect of Ti³⁺/Ti⁴⁺ active sites dynamic on reaction pathways in direct gas-solid-phase CO₂ photoreduction

Converting CO₂ to CH₄ by solar-powered catalysis involves complex steps that produce a range of by-products. Therefore, designing efficient heterostructures for a particular chemical synthesis is challenging. The optimisation of photocatalyst surfaces can achieve the desired CO₂ photoreduction pathway. Herein, we developed TiO₂/CdSe nanocrystals with both amorphous and crystalline TiO₂ surfaces. In situ EXAFS analysis revealed that the amorphous surface contains abundant active Ti³⁺ sites, while the crystalline surface is limited. Moreover, the amorphous surface of TiO₂/CdSe exhibits self-regenerating Ti³⁺ active sites, which enable a novel CH₄ cycle. Density functional theory calculation showed that an amorphous structure enhances electron transfer and localisation to Ti³⁺, favouring CO₂ adsorption. In situ DRIFTS analysis showed different CO₂ to CH₄ pathways on both surfaces. These results show the potential for enhanced photocatalytic CO₂ reduction through surface engineering, which has far-reaching implications for sustainable energy conversion.