Defective Nb 2 C MXene Cocatalyst on TiO 2 Microsphere for Enhanced Photocatalytic CO 2 Conversion to Methane.

Sustainable and scalable solar-energy-driven CO 2 conversion into fuels requires earth-abundant and stable photocatalysts. In this work, a defective Nb 2 C MXene as a cocatalyst and TiO 2 microspheres as photo-absorbers, constructed via a coulombic force-driven self-assembly, is synthesized. Such photocatalyst, at an optimized loading of defective Nb 2 C MXene (5% def-Nb 2 C/TiO 2 ), exhibits a CH 4 production rate of 7.23 µmol g -1  h -1 , which is 3.8 times higher than that of TiO 2 . The Schottky junction at the interface improves charge transfer from TiO 2 to defective Nb 2 C MXene and the electron-rich feature (nearly free electron states) enables multielectron reaction of CO 2 , which apparently leads to high activity and selectivity to CH 4 (sel. 99.5%) production. Moreover, DFT calculation demonstrates that the Fermi level (E F ) of defective Nb 2 C MXene (-0.3 V vs NHE) is more positive than that of Nb 2 C MXene (-1.0 V vs NHE), implying a strong capacity to accept photogenerated electrons and enhance carrier lifetime. This work gives a direction to modify the earth-abundant MXene family as cocatalysts to build high-performance photocatalysts for energy production.