Pseudocapacitance: Mechanism and Characteristics

Pseudocapacitance is a mechanism of charge storage in electrochemical devices, which has the capability of delivering higher energy density than conventional electrochemical double-layer capacitance and higher power density than batteries. In contrast to electric double-layer capacitors (EDLC) where charge storage is mainly due to the electrostatic interaction of ions in the electrolyte with the electrode, in pseudocapacitors charge storage between the electrode–electrolyte interface is associated with a highly reversible redox reaction or intercalation. Though by definition pseudocapacitors involve faradic processes, they are largely different from faradic processes that occur in batteries. With extensive research and development of nanoscale materials, which give different electrochemical capacitive signatures for varying particle size, the definition of pseudocapacitance is highly misinterpreted and often a battery-type material is reported as pseudocapacitive material, misreporting the capacitance to exaggerated values. There is a lack of understanding among the electrochemical research community in differentiating the pseudocapacitive process from others. This chapter aims to provide a comprehensive note on understanding the fundamentals of pseudocapacitance, its origin, and different type of pseudocapacitive charge storage mechanisms. The electrochemical characteristics of pseudocapacitive along with that of EDLC and battery-type material are discussed to help the reader understand the differentiation.