Heteroatom doping in 2D MXenes for energy storage/conversion applications

MXenes (inorganic metal carbides, nitrides, and carbonitrides) are currently the rising star of two-dimensional (2D) family. After its discovery in 2011, initial research was concentrated on pristine MXenes only. However, in the last few years, the MXene family has been expanded with the exploration of novel double MXenes, synthesis of non-Ti MXenes, and heteroatom doping of MXenes. The current review article delivers an exclusive overview of the current research trends on the heteroatom doping of MXenes. The recent advances in heteroatom doping of MXenes (majorly Ti-MXenes) for energy storage/conversion applications including secondary batteries (Li-ion, Li–S, Na–S, Na-ion, K-ion, Zn-ion batteries), supercapacitors, electrocatalysis, etc. are summarized. A brief overview of the defects as well as doping in various 2D materials is included in the manuscript. Various doping strategies of MXenes are outlined. Moreover, the impact of artificial intelligence/machine learning on MXene research is also concisely discussed. Additionally, the advantages of doping on MXenes are discussed in detail. Lastly, the existing challenges and future prospects of doped MXenes are addressed. It is expected that the current review will open new prospects for the fabrication of advanced energy devices through heteroatom doping of MXenes.