Synthesis, Structure Regulating and the Applications in Electrochemical Energy Storage of MXenes

MXenes have attracted intensive research attention owing to its unique two-dimensional layered structure, high specific surface area, excellent conductivity, superior surface hydrophilicity and chemical stability. In recent years, selectively etching the A element layers from MAX phases by fluoride-containing etchants (HF, LiF-HCl, etc) is a common method to prepare multilayer MXenes with plentiful surface terminations. Due to the pollution problems of fluoride-containing etchants, at present, many studies have been reported on the use of more green and environmentally friendly fluorine-free etchants (NaOH, ZnCl2, etc) to etch MAX phases. The properties of MXenes are closely related to its structure. Additionally, it is found that the preparation methods have great impacts on the layer spacing and surface terminations of MXenes, consequently affecting its performance. Hence, this paper summarizes and compares the research progress of the preparation strategies , layer spacing and surface terminations regulation of MXenes. Then the applications of MXenes in electrochemical energy storage are outlined. Finally, the challenges and prospects for the future development of MXenes are also proposed.