Dissolved redox species for the improvement of the performance of supercapacitors

The recent surging investigations into the applications of redox active electrolytes for the improvement of charge storage in supercapacitors and other related hybrid devices have shown a lot of promise but also revealed a number of challenges. This review aims at providing a critical analysis of up-to-date research and development in the use of dissolved redox species in electrolytes for supercapacitors. The challenges and confusions inherent in the description of the charge storage metrics, particularly charge capacity and capacitance, are carefully appraised. The role of the carbon electrode properties such as surface area and surface functionality are explained from the standpoint of the interactions of these redox species with the carbon electrode/ electrolyte (E/E) interface. Different strategies that have been adopted for the improvement of practical devices using redox electrolytes are reviewed. Furthermore, brief descriptions on some promising progresses in this increasingly important research area are provided.