Redox-based supercapacitor materials: a review

Advancements in new efficient electrochemical energy storage materials are urgently needed to meet upcoming societal and environmental requirements. The global demand for efficient and sustainable electrochemical energy storage has motivated commercial and scientific communities to pursue novel ideas and discover new experimental techniques in sophisticated capacitor research. Capacitors are electricity storing devices that can be rapidly charged and discharged and they are essential building blocks of electrical circuits ranging from minute microprocessors to gigantic power supplies. Unlike batteries, capacitors have a low capability to store electrical energy. Redox materials with tailored features are used as electrodes and electrolytes of electrochemical supercapacitors because they provide good energy density, with no compromise to their high power density and exceptional cyclability. Specifically, electrode materials that involve redox reactions of electrolyte ions are predicted to bridge the gap between conventional capacitors with the high power density and classical batteries with high energy density. In this work, redox-based electrode and electrolyte materials are reviewed to understand how their structure, properties, and mechanisms can be tailored to obtain improved electrochemical performance of the supercapacitors for future sustainable energy storage applications