Quantum capacitance: The large but hidden capacitance in supercapacitors

Increasing energy storage demands, and the reducing device size have led to the development of high surface area nanoporous materials. However, the energy storage in such materials do not typically scale as expected according to the increase in the surface area. This is because of another capacitance that appears in series with the electric double-layer capacitors used for energy storage. This capacitance is termed quantum capacitance, which is although present in all materials but becomes considerable in value for materials with low density of electronic states. The quantum capacitance and its effects can greatly enhance our understanding of the double-layer capacitance. In this review, we present the understanding built behind quantum capacitance based on some of the some recent work elucidating the vastness of the area that can be explored.