Ion transport behaviors in MXenes for electrochemical energy storage and conversion

MXenes, an innovative class of two-dimensional (2D) materials composed of transition-metal carbides and/or nitrides, have garnered significant interest for their potential in energy storage and conversion applications, which is largely attributed to their modifiable surface terminations, exceptional conductivity, and favorable hydrophilic characteristics. MXenes show various ion transport behaviors in applications like electrochemical catalysis, supercapacitors, and batteries, encompassing processes like electrostatic adsorption of surface ions, redox reactions of ions, and interlayer ion shuttle. This review aims to present a summary of advancements in the comprehension of ion transport behaviors of Ti₃C₂T _x MXenes. First, the composition, properties, and synthesis techniques of MXenes are concisely summarized. Subsequently, the discussion delves into the mechanisms of ion transport in MXenes during CO₂ reduction, water splitting, supercapacitor operation, and battery performance, elucidating the factors determining the electrochemical behaviors and efficacy. Furthermore, a compilation of strategies used to optimize ion transport behaviors in MXenes is presented. The article concludes by presenting the challenges and opportunities for these fields to facilitate the continued progress of MXenes in energy-related technologies.