Schottky−Defect–Photothermal Coupling in Nb ₂ C/Nb ₂ O _{5– <i>x</i>} Heterostructures for Enhanced CO ₂ Photoreduction

Photocatalytic reduction of CO2 into carbon-based fuels offers a viable approach for solar-to-chemical energy conversion but remains limited by inefficient charge separation and the intrinsic inertness of CO2. Overcoming these challenges requires rationally engineered heterostructures capable of simultaneously accelerating charge transport and activating CO2 molecules. Here, a well-defined Nb2C/Nb2O5–x hybrid photocatalyst is developed via controlled partial oxidation of Nb2C MXene. Comprehensive time-resolved and in situ spectroscopic analyses reveal a Schottky-governed interfacial charge-transfer pathway in which photogenerated holes in Nb2O5–x rapidly migrate to Nb2C for water oxidation, while electrons remain within the Nb2O5–x domains to drive CO2 reduction. The in situ-formed Nb2O5–x nanodomains contain abundant oxygen vacancies that act as electron-storing centers, extending carrier lifetimes, enhancing CO2 adsorption and bending, and lowering the free-energy barrier of the rate-determining step during the CO2 conversion. The metallic Nb2C substrate provides high conductivity and generates a pronounced photothermal effect under illumination, locally elevating the surface temperature to thermodynamically promote endothermic CO2 chemisorption. Benefiting from this integrated Schottky–defect–photothermal coupling mechanism, the Nb2C/Nb2O5–x heterostructure delivers enhanced CO2 reduction activity compared with pristine Nb2O5–x and Nb2C, establishing a broadly applicable design paradigm for MXene-derived photocatalysts featuring cooperative charge transfer and thermally assisted molecular activation.