Pseudocapacitor

Scheme on double layer on electrode (BMD model).
1. IHP Inner Helmholtz Layer
2. OHP Outer Helmholtz Layer
3. Diffuse layer
4. Solvated ions
5. Specifically adsorptive ions (Pseudocapacitance)
6. Solvent molecule.

Hierarchical classification of supercapacitors and related types

Pseudocapacitors ^[1] store electrical energy faradaically by electron charge transfer between electrode and electrolyte. This is accomplished through electrosorption, reduction-oxidation reactions (redox reactions), and intercalation processes,^[2] termed pseudocapacitance.

A pseudocapacitor is part of an electrochemical capacitor, and forms together with an electric double-layer capacitor (EDLC) to create a supercapacitor.

A pseudocapacitor has a chemical reaction at the electrode, unlike EDLCs where the electrical charge storage is stored electrostatically with no interaction between the electrode and the ions. An example is a redox reaction where the ion is O2+ and during charging, one electrode hosts a reduction reaction and the other an oxidation reaction. Under discharge the reactions are reversed.

Unlike batteries, in faradaic electron charge-transfer ions simply cling to the atomic structure of an electrode. This faradaic energy storage with only fast redox reactions makes charging and discharging much faster than batteries.

Double-layer capacitance and pseudocapacitance combine to produce a supercapacitor's capacitance value. Pseudocapacitance may be higher by a factor of 100 than double-layer capacitance with the same electrode surface.

References

1. ↑ B. E. Conway (1999) (in German), Electrochemical Supercapacitors: Scientific Fundamentals and Technological Applications, Berlin: Springer, pp. 1-8, ISBN 0306457369, //books.google.com/books?id=8yvzlr9TqI0C&pg=PA1  See also Brian E. Conway in Electrochemistry Encyclopedia: ELECTROCHEMICAL CAPACITORS Their Nature, Function, and Applications
2. ↑ Marin S. Halper, James C. Ellenbogen, Supercapacitors: A Brief Overview, MITRE, March 2006