Redox Materials for Electrochemical Capacitors

Abstract

Electrochemical capacitors are known for their high power density and cyclability, and various redox reactions can be utilized to improve their energy density. A great variety of redox materials have been investigated recently for use in electrochemical capacitors, not only transition metal oxides, which have been studied for many years. In this review, we provide a comprehensive explanation of redox materials for electrochemical capacitors. Manganese oxides and ruthenium oxides, which are typical metal oxides exhibiting pseudocapacitance, are first discussed. Nickel oxides used in hybrid capacitors are also covered. Various 0D and 2D nanomaterials are highlighted. Pseudo-capacitance using nanosized complex materials and metal-organic frameworks is also presented. Furthermore, electrolyte systems that exhibit redox characteristics for electrochemical capacitors are also reviewed.