Nanoarchitectonics of MXene/semiconductor heterojunctions toward artificial photosynthesis via photocatalytic CO2 reduction

Artificial photosynthesis via photocatalytic CO2 reduction to transform CO2 into C1/C2 hydrocarbon fuels represents a fundamental solution to energy shortage and global warming. The main challenges in this process are the low CO2 adsorption and activation stability and low utilization rate of the charge carriers. Two-dimensional transition metal carbides (MXenes) have been explored as cocatalysts to improve the charge separation efficiency and CO2 adsorption/activation power and thereby increase the photocatalytic CO2 reduction activity. In this study, we identify the role of MXenes in heterojunction photocatalytic CO2 reduction and provide some suggestions for preparing MXene-based heterojunction photocatalysts. First, we elaborate on the effect of surface terminations on the electronic structure of MXenes, such as the bandgap and work function. Subsequently, we provide a detailed discussion on the role of MXenes in photocatalytic CO2 reduction: they can serve as electron/hole reservoirs, provide abundant CO2 adsorption and activation sites, and exhibit photothermal conversion characteristics. Moreover, we expound on the photocatalytic CO2 reduction pathways on MXene heterojunction photocatalysts. Finally, the challenges and prospects of MXenes for photocatalytic CO2 reduction are discussed.