Pseudokapacitans

Pseudokapacitance, sometimes written as pseudocapacitance and appearing in some languages as pseudokapacitans, refers to a mode of charge storage in electrochemical systems where fast, reversible faradaic (redox) reactions occur at or near the electrode surface, producing a capacitive-like charge–voltage response. It is an energetic component of devices called pseudocapacitors and is distinct from electric double-layer capacitance, which arises from nonfaradaic charge separation. In English literature, the term pseudocapacitance is standard, while pseudokapacitans may appear as a plural form in non-English contexts.

Mechanisms include fast surface redox reactions, adsorption processes, and near-surface intercalation in conducting materials. These processes enable high specific capacitance and good rate performance, often surpassing pure double-layer storage, while avoiding full diffusion-controlled limits typical of batteries. Common pseudocapacitive materials are transition metal oxides such as MnO2, RuO2, NiO, and Co3O4; conducting polymers like polyaniline, polypyrrole, and PEDOT; and layered or nanostructured materials such as MXenes (Ti3C2Tx). Composites and engineered nanostructures are frequently employed to improve electrical conductivity and ion transport.

Characterization relies on cyclic voltammetry and galvanostatic charge–discharge, with the current response reflecting faradaic contributions that can be capacitive-like. A common diagnostic uses the power-law relation between peak current and scan rate (i ∝ v^b), where b near 1 indicates capacitive behavior and lower values indicate diffusion control. Pseudokapacitance can increase the energy density of supercapacitors and hybrid devices while offering substantial power delivery. Challenges include cycle stability, structural changes during redox cycling, and material cost, guiding ongoing research into durable, scalable systems.