Beyond Ti-based MXenes: A review of emerging non-Ti based metal-MXene structure, properties, and applications

MXene is one of the most interesting two-dimensional (2D) materials that have been discovered. With more than 70% of publication-related studies, titanium-based MXene (Ti-MXene) has been well-evaluated, hence, laying the very first foundation of the 2D MXene with tailorable properties acquainted with a diverse range of applications. Yet there are still other candidates amongst transitional metals that can play the role of 2D MXene well beyond known applications. In this critical review, we provide a systematic discussion of the preparations, properties, challenges, key findings, and applications of less-evaluated M-MXene where M represents other non-Ti transitional metals. In certain applications, such as electrocatalysis and energy storage, the remarkable properties of non-Ti MXene exceed the performance of conventional Ti-MXene. Indeed, there has been a lot of progress in the top-down and bottom-up synthesis of MXenes that can precisely control the properties of M-MXene catering advanced applications. From the main challenges in preparing complicated M-MXenes to the choice of their applications accordingly to their well-established properties, this review provides a comprehensive evaluation of published studies. This review also studies the progress in double metal combinations, and other metal candidates expanded outside the IIIB to VIB family group and the further expansion of the 2D metal carbide/nitride/carbonitride to the 2D metal boride family. Lastly, this critical review ends with the prospects and further suggestions for the direction of MXene in nanomaterial development.