Pseudocapacitance: An Introduction

An electrochemical energy storage device that can deliver high power and energy density is needed globally. To accomplish this one method adopted involves the use of pseudocapacitive materials that use reversible surface or near-surface Faradaic processes to store charges. By doing so, they can overcome the mass transfer and capacity limits of batteries and electrical double-layer capacitors. Both chemical and electrostatic processes are used to store charges in pseudocapacitors. Pseudocapacitors have a charge transfer process that is comparable to that of a battery. There is a greater rate of transfer because of the use of a thinner redox material on the electrode or less ion penetration into the structure from the electrolyte. Technology is still in need of development in materials performance and device reliability. Research is still being done to determine the materials and electrochemical properties that can produce high energy density at quicker charge–discharge rates. In this context, transition metal oxides are attractive. With this as the background, the latest developments in pseudocapacitor materials and devices are discussed here.