Recent progress in layered transition metal carbides and/or nitrides (MXenes) and their composites : synthesis and applications

Abstract

Since its inception in 2011, from the inaugural synthesis of multi-layered Ti3C2Tx by etching Ti3AlC2 with hydrofluoric acid (HF), novel routes with myriad of reducing agents, etchants and intercalants have been explored and added many new members to the two-dimenisonal (2D) material constellation. Despite being endowed with the rare combination of good electronic conductivity and hydrophilicity, their inherent low capacities, for instance, temper their prospect in application for electrodes in energy storage systems. MXene-based composites, however, with probable synergistic effect in agglomeration prevention, facilitating electronic conductivity, improving electrochemical stability, enhancing pseudocapacitance and minimizing the shortcomings of individual components, exceed the previously mentioned capacitance ceiling. In this review, we summarise the development and progress in synthesis of various multi-layered carbides, carbonitrides and nitrides, intercalants, as well as the subesequent processing in order to delaminate them into single- and/or few-layered and modifications to MXene-based composites, focusing on their performances and applications as transparent conductive films, environmental remediation, electromagnetic interference (EMI) absorption and shielding, electrocatalysts, Li-ion batteries (LIBs), supercapacitors and other electrochemical storage systems.