Precise Engineering of Cobalt Sites on Strained TiO_2-x Enables Tunable Syngas Production via Photocatalytic CO₂ and...

Photocatalytic CO₂-to-syngas conversion represents a sustainable approach to addressing global energy and environmental challenges, yet its practical efficiency is often hindered by poorly defined active sites and sluggish reaction kinetics. In this work, we construct well-defined cobalt single-atom (Co_SA) and cobalt nanoparticle (Co_NP) sites anchored on strained TiO_2-x through an in situ topological transformation of a bimetallic Co-Ti-ethylene glycolate metal-organic framework (Co-Ti-EG BMOF) precursor. The Co_SA sites exhibit highly selective reduction of CO₂ to CO, achieving a production rate of 329.0 μmol g^-1 over 5 h, whereas the Co_NP sites predominantly facilitate the hydrogen evolution reaction, yielding 123.7 μmol g^-1 of H₂ without the use of sacrificial reagents. Owing to the distinct site-specific functionalities and enhanced charge separation imparted by the strained TiO_2-x matrix, the catalyst enables precise tuning of syngas composition, with CO:H₂ ratios adjustable from 0.08 to 6.78. Furthermore, the incorporation of an organic solvent improves the reactant solubility, thereby significantly enhancing both product yields and syngas selectivity. This study presents a rational design strategy for multifunctional photocatalytic systems aimed at controllable and efficient CO₂ valorization.