Defective Nb₂C MXene Cocatalyst on TiO₂ Microsphere for Enhanced Photocatalytic CO₂ Conversion to Methane

Abstract

Sustainable and scalable solar‐energy‐driven CO2 conversion into fuels requires earth‐abundant and stable photocatalysts. In this work, a defective Nb2C MXene as a cocatalyst and TiO2 microspheres as photo‐absorbers, constructed via a coulombic force‐driven self‐assembly, is synthesized. Such photocatalyst, at an optimized loading of defective Nb2C MXene (5% def‐Nb2C/TiO2), exhibits a CH4 production rate of 7.23 µmol g−1 h−1, which is 3.8 times higher than that of TiO2. The Schottky junction at the interface improves charge transfer from TiO2 to defective Nb2C MXene and the electron‐rich feature (nearly free electron states) enables multielectron reaction of CO2, which apparently leads to high activity and selectivity to CH4 (sel. 99.5%) production. Moreover, DFT calculation demonstrates that the Fermi level (EF) of defective Nb2C MXene (−0.3 V vs NHE) is more positive than that of Nb2C 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.