Recent advances in MXenes: beyond Ti-only systems

Since the first report on Ti3C2Tx in 2011, the number of reports on 2D transition metal carbides and nitrides, known as MXenes, has increased rapidly. Most of the reports have focused on Ti-based MXenes due to their ease of synthesis and striking properties; however, MXenes beyond Ti-only systems have also been recently reported to exhibit intriguing electronic, magnetic, optical, and mechanical properties. This forward-looking review aims to summarize the research trends, synthesis, properties, and applications of non-Ti MXenes to motivate researchers to unearth the characteristics and unleash the full potential of less explored MXenes. Furthermore, the properties and applications of theoretically predicted non-Ti MXenes are also highlighted to stimulate further research in synthesizing them experimentally. Finally, the challenges to be addressed and future research directions are presented.