Tunable syngas production from photocatalytic CO₂ reduction with mitigated charge recombination driven by spatially separated cocatalysts

Photocatalytic CO₂ reduction represents a sustainable route to generate syngas (the mixture of CO and H₂), which is a key feedstock to produce liquid fuels in industry. Yet this reaction typically suffers from two limitations: unsuitable CO/H₂ ratio and serious charge recombination. This paper describes the production of syngas from photocatalytic CO₂ reduction with a tunable CO/H₂ ratio via adjustment of the components and surface structure of CuPt alloys and construction of a TiO₂ mesoporous hollow sphere with spatially separated cocatalysts to promote charge separation. Unlike previously reported cocatalyst-separated hollow structures, we firstly create a reductive outer surface that is suitable for the CO₂ reduction reaction. A high evolution rate of 84.2 μmol h^-1 g^-1 for CO and a desirable CO/H₂ ratio of 1:2 are achieved. The overall solar energy conversion yield is 0.108%, which is higher than those of traditional oxide and sulfide based catalysts (generally about 0.006-0.042%). Finally, density functional theory calculations and kinetic experiments by replacing H₂O with D₂O reveal that the enhanced activity is mainly determined by the reduction energy of CO∗ and can be affected by the stability of COOH∗.