2D MXenes: high-performance supercapacitors for future energy systems

Abstract

The increasing demand for advanced energy storage in applications like wearable electronics, electric vehicles, and renewable technologies encourages the growth of advanced supercapacitor materials. MXenes, which are two-dimensional compounds made of transition metals, carbides, nitrides, and carbonitrides, attract attention as promising electrode materials due to their strong electrical conductivity, flexibility, water attraction, and easily altered surface chemistry. This review covers significant progress in MXene-based supercapacitors, discussing methods of making them, their structure and the performance characteristics within the realm of pseudocapacitive energy storage mechanisms in supercapacitor architectures, and how they are incorporated into devices. Methods for synthesis, such as HF etching, fluoride processes, and new environmentally friendly approaches with alkali and electrochemistry, are examined, and their role in surface alterations and scale-up efforts is emphasized. Physicochemical characteristics of MXenes, including high specific surface area, pseudo-capacitive properties, and good cycling, are investigated to determine their suitability for flexible, solid-state, and micro-supercapacitors. The blending of MXene with carbon, conductive polymers, and metal oxides in electrodes addresses restacking and oxidation, enhancing storage capacity (250–700 F g⁻¹) and energy density (20–70 Wh kg⁻¹). Although they appear promising for use in supercapacitors, MXene-based devices face difficulties in manufacturing due to oxidation stability and safety. Future developments are expected to introduce new materials, promote eco-friendly synthesis, and advance design for wearable, connected devices. Overall, this review consolidates the current understanding and technological progress of MXene-based supercapacitors and outlines pathways for translating their lab-scale success into practical applications.