Redox active electrolytes in carbon/carbon electrochemical capacitors

The application of redox-active electrolytes to realize carbon/carbon electrochemical capacitors has created a great opportunity to enhance the mediocre energy of these devices. Taking advantage of the faradic current from the redox transformation of electrolyte species, which generates a large capacity at one electrode, the resulting hybrid cells can store twice more energy than typical electrical double-layer capacitors based on the same carbon electrode material. However, among a relatively large number of tested redox active electrolytes, only few are acknowledged to provide ideally performing hybrid capacitors. This review critically discusses the literature data and provides clues for realizing optimized systems.