pseudocapacitive

Pseudocapacitive refers to energy storage in electrochemical capacitors that arises from fast, reversible faradaic (redox) reactions at or near the surface of electrode materials. This provides a capacitive-like current response while involving electron transfer, in contrast to purely electrostatic charge storage at the electrode–electrolyte interface.

The pseudocapacitive charge stems from surface redox processes of transition metal oxides (such as RuO2, MnO2), conducting polymers (polyaniline, polypyrrole, PEDOT), and certain carbides or nitrides such as MXenes. Reactions occur within a few nanometers of the surface and can involve intercalation, adsorption, or fast surface redox, enabling high rate capability. The measured capacitance is often described as C_p in addition to any electric double-layer capacitance.

Characterization typically relies on cyclic voltammetry showing redox features or broad quasi-rectangular shapes, galvanostatic charge–discharge with good rate performance, and impedance spectroscopy to identify pseudocapacitive contributions. Distinguishing pseudocapacitance from electric double-layer capacitance can require deconvolution of the total capacitance and analysis of its dependence on scan rate and potential.

Pseudocapacitive materials offer higher energy density than pure double-layer devices while maintaining fast power delivery, making them attractive for advanced supercapacitors and hybrid energy storage systems. Challenges include chemical and structural stability under cycling, conductivity limitations, and potential degradation of active materials over time.