pseudokapazitives

Pseudocapacitance, sometimes referred to as pseudokapacitance, is a type of electrochemical energy storage mechanism in which charge is stored through fast, reversible Faradaic reactions at or near the surface of an electrode. Unlike purely electrostatic electric double-layer capacitance, pseudocapacitance involves electron transfer and redox processes that contribute to a capacitive response at high rates.

The mechanism involves fast surface redox reactions (surface faradaic processes) or interfacial intercalation pseudocapacitance, where ions insert into a material's near-surface region with rapid charge transfer. The result is a capacitance contribution that follows quasi-rectangular charge–discharge behavior in many cases, or distinct redox features in voltage profiles, particularly at high scan rates.

Common pseudocapacitive materials include transition metal oxides and hydroxides such as MnO2, RuO2, IrO2, and NiO, as well as conducting polymers like polyaniline and polypyrrole. Some transition metal sulfides and oxyhydroxides also exhibit pseudocapacitive behavior. In addition, certain carbon-based materials show pseudocapacitance when surface functional groups or defects provide reversible redox activity. The overall performance depends on the material, structure, and electrolyte.

In devices, pseudocapacitance adds to the electric double-layer capacitance to yield higher total capacitance and often improved rate capability, with energy density higher than EDLCs but sometimes at the expense of cycle stability. Pseudocapacitors are commonly used in supercapacitors and hybrid energy storage systems. Characterization relies on cyclic voltammetry, galvanostatic charge–discharge, and methods that separate Faradaic and non-Faradaic contributions.