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

Photocatalytic reduction of CO 2 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 CO 2 . Overcoming these challenges requires rationally engineered heterostructures capable of simultaneously accelerating charge transport and activating CO 2 molecules. Here, a well-defined Nb 2 C/Nb 2 O 5– x hybrid photocatalyst is developed via controlled partial oxidation of Nb 2 C MXene. Comprehensive time-resolved and in situ spectroscopic analyses reveal a Schottky-governed interfacial charge-transfer pathway in which photogenerated holes in Nb 2 O 5– x rapidly migrate to Nb 2 C for water oxidation, while electrons remain within the Nb 2 O 5– x domains to drive CO 2 reduction. The in situ-formed Nb 2 O 5– x nanodomains contain abundant oxygen vacancies that act as electron-storing centers, extending carrier lifetimes, enhancing CO 2 adsorption and bending, and lowering the free-energy barrier of the rate-determining step during the CO 2 conversion. The metallic Nb 2 C substrate provides high conductivity and generates a pronounced photothermal effect under illumination, locally elevating the surface temperature to thermodynamically promote endothermic CO 2 chemisorption. Benefiting from this integrated Schottky–defect–photothermal coupling mechanism, the Nb 2 C/Nb 2 O 5– x heterostructure delivers enhanced CO 2 reduction activity compared with pristine Nb 2 O 5– x and Nb 2 C, establishing a broadly applicable design paradigm for MXene-derived photocatalysts featuring cooperative charge transfer and thermally assisted molecular activation.