Pseudocapacitor

Main article: Supercapacitor
Hierarchical classification of supercapacitors and related types
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.

Pseudocapacitors 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, termed pseudocapacitance.[1][2][3]

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

Pseudocapacitance and double-layer capacitance add up to a common inseparable capacitance value of a supercapacitor. However, they can be effective with very different parts of the total capacitance value depending on the design of the electrodes. A pseudocapacitance may be higher by a factor of 100 as a double-layer capacitance with the same electrode surface.

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. Pseudocapacitance is accompanied by an electron charge-transfer between electrolyte and electrode coming from a de-solvated and adsorbed ion. One electron per charge unit is involved. The adsorbed ion has no chemical reaction with the atoms of the electrode (no chemical bonds arise[4]) since only a charge-transfer take place. 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.

Electrochemical pseudocapacitors use metal oxide or conductive polymer electrodes with a high amount of electrochemical pseudocapacitance. The amount of electric charge stored in a pseudocapacitance is linearly proportional to the applied voltage. The unit of pseudocapacitance is farad.

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 (March 2006). Supercapacitors: A Brief Overview (PDF) (Technical report). MITRE Nanosystems Group. Retrieved 2014-01-20.
  3. ↑ E. Frackowiak, F. Beguin: Carbon Materials For The Electrochemical Storage Of Energy In Capacitors. In: CARBON. 39, 2001, S. 937–950 (PDF) E. Frackowiak, K. Jurewicz, S. Delpeux, F. Béguin: Nanotubular Materials For Supercapacitors. In: Journal of Power Sources. Volumes 97–98, Juli 2001, S. 822–825, doi:10.1016/S0378-7753(01)00736-4.
  4. ↑ Garthwaite, Josie (12 July 2011). "How ultracapacitors work (and why they fall short)". Earth2Tech. GigaOM Network. Retrieved 23 April 2013.
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