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.