Advancements in 2D MXene-based supercapacitor electrodes: synthesis, mechanisms, electronic structure engineering, flexible wearable energy storage for real-world applications, and future prospects

Abstract

Supercapacitors are widely recognized as a favorable option for energy storage due to their higher power density compared to batteries, despite their lower energy density. However, to meet the growing demand for increased energy capacity, it is crucial to explore innovative materials that can enhance energy storage efficiency. Recent research has focused on investigating various electrode materials for use in supercapacitors, with particular attention given to MXenes. MXenes exhibit immense potential for energy storage due to their unique characteristics, including a 2D van der Waals layered structure, small band gaps, hydrophilic surface, excellent electrical conductivity, high specific surface area, and active redox sites on the surface facilitated by transition metals. These attributes collectively contribute to their promising stability, energy and power density, and overall lifespan. This comprehensive review explores a diverse array of topics pertaining to the latest 2D MXene-based supercapacitor electrodes. It encompasses discussions on different synthesis methods, electrode structures, the underlying working mechanisms, and the impact of electrolytes on supercapacitor performance. Additionally, a concise overview of various types of MXene materials is presented, ranging from titanium-based MXenes to niobium-based MXenes, vanadium-based MXenes, molybdenum-based MXenes, and tantalum-based MXenes. Furthermore, this review focuses on electronic structure engineering strategies such as heterostructures based on MXenes, heteroatom-doping based on MXenes, polymer based MXenes, and ternary composites based on MXenes, all of which contribute to improving the electrochemical performance of supercapacitors. The review thoroughly examines the advantages and disadvantages of MXene-based supercapacitor electrodes, offering a comprehensive understanding of their strengths and limitations. Additionally, it discusses the structural stability of MXene-based electrodes after electrochemical testing, as well as their applications in daily human life, particularly focusing on the uses of MXene-based flexible wearable energy storage for real-world applications. In the end, the challenges and prospects of MXenes in supercapacitors are discussed.