A Review of Advanced Electrode Materials for Supercapacitors: Challenges and Opportunities

Supercapacitors, also known as electrochemical capacitors, store energy either by the adsorption of ions (electric double-layer capacitors) or by fast redox reactions at the surface (pseudocapacitors). When high power delivery or uptake is required in electrical energy storage and harvesting applications, they can complement or replace batteries. The fundamental and applied aspects of supercapacitors have seen rapid progress in recent years. With the development of advanced nanostructured materials and a better understanding of charge storage mechanisms, significant performance improvements have been achieved. In this review, the latest advances in supercapacitors in charge storage mechanisms and electrode materials is discussed. We describe the working principle and challenges of different advanced materials used as supercapacitor electrodes and strategies to overcome these challenges. The focus is on materials like metal sulfides, metal oxides, conducting polymers, MXenes, metal–organic frameworks, and covalent organic frameworks. The performance of electrode materials is analyzed by parameters including energy density, capacitance, power density, cyclic stability, and rate capability. The prospects and challenges related to supercapacitors in applied applications are also discussed.