Removing roadblocks and opening new opportunities for MXenes

The 2D carbides and nitrides, known as MXenes, are among the most recent, and quickly expanding, material families. The field is experiencing very fast growth with the number of papers on MXenes roughly doubling every year since their discovery in 2011. Great progress in synthesis and control of MXene properties has since been achieved. Synthesis of numerous theoretically predicted MXenes, including ordered solid solutions and highentropy structures, led to the exploration of numerous applications. MXenes are not only promising candidates for energy storage and related electrochemical applications, such as electrocatalysis, but also applications in optoelectronics, plasmonics, electromagnetic interference shielding, medicine, sensing, catalysis and water desalination. We particularly focus on key material manufacturing and stability issues. We describe the scalable synthesis of MXenes by selective etching in aqueous acidic solutions; alternative synthesis methods, particularly fluorine-free synthesis; delamination without the use of organic intercalants; and improving the environmentally stability and shelf life of MXenes in colloidal suspensions. Finally, we discuss the current understanding of electronic transport in MXene films, which is of critical importance for many MXene applications.