Advancements in supercapacitors: breaking barriers and enabling amazing applications

Supercapacitors (SCs) display intrinsic advantages such as high power density and high rate capability but low energy density. Thus, the development of advanced pseudocapacitive electrode materials is crucial for the advancement of supercapacitor technologies. These electrode materials significantly influence the performance of supercapacitors in electrical energy storage (EES) systems in terms of energy density and cycling stability. In this review, we first discuss EES technologies and their development and types of SCs, followed by an overview of the importance of organic electrode materials in pseudocapacitor (PSC) applications. Moreover, we present the principles of different redox-active organic molecule design strategies and their theoretical calculations to understand their electrochemical characteristics. Furthermore, we highlight the role of redox-active organic electrode materials in achieving a wider potential voltage window and, in turn, higher energy density, thus enhancing the electrochemical performance of PSCs. Subsequently, we discuss the role of molecular structures, the composition of electronic conducting materials and their structural and electrochemical performance relationship. Moreover, we highlight the advantages and disadvantages of organic materials compared with traditional transition-metal oxide inorganic materials for PSCs. Then, we present a brief discussion on the advances in small redox-active molecular architectures and their use in the fabrication of novel electrode materials, including polymers, covalent organic frameworks and metal organic frameworks. We provide an in-depth discussion on how material development from small redox-active molecules advances the charge-storage field and their application in illuminating light-emitting diodes. We hope that this review article will help provide a fundamental basis for the design and development of next-generation pseudocapacitive electrode materials from renewable sources for sustainable supercapacitor systems with higher charge-storage capability.