A review of 3D porous MXene architectures: Design strategies and diverse electrochemical applications

The increasing energy crises and environmental pollution highlight the urgent requirement for exceptional functional materials. Two-dimensional (2D) transition metal carbides and/or nitrides (MXenes) are garnering growing interest and demonstrating competitive electrochemical applications in energy and environment due to their outstanding electrical conductivity, plentiful surface functional groups, excellent dispersibility, and high specific surface area. However, the aggregation and self-restacking of 2D MXene nanosheets are typically unavoidable throughout electrode fabrication, which will restrict the accessibility of their active sites and ion diffusion channels, and compromise their electrochemical properties. The creation of three-dimensional (3D) porous structures using 2D MXene nanosheets has been verified as a successful approach for enhancing surface utilization efficiency and reducing ion and mass transport distances, leading to the advancement of MXene and MXene-based composites with outstanding electrochemical performance. This review outlines some common approaches to construct 3D porous MXene architectures, including spray drying, template, assembly, gas foaming and 3D Printing methods. Meanwhile, the structure–property relationships of 3D porous MXenes and their electrochemical applications, such as supercapacitors, Li-ion battery, electrocatalysis, and electrosorption, are also pointed. Finally, the authors present a concise overview of on the potential, challenges, and future opportunities of 3D porous MXenes.