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[[File:Electric double-layer (BMD model) NT.PNG|thumb|200px|Scheme on double layer on electrode (BMD model).<br/> 1. IHP Inner Helmholtz Layer<br/> 2. OHP Outer Helmholtz Layer<br/> 3. Diffuse layer<br/> 4. Solvated ions<br/> '''5. |
[[File:Electric double-layer (BMD model) NT.PNG|thumb|200px|Scheme on double layer on electrode (BMD model).<br/> 1. IHP Inner Helmholtz Layer<br/> 2. OHP Outer Helmholtz Layer<br/> 3. Diffuse layer<br/> 4. Solvated ions<br/> '''5. Specifically adsorptive ions (Pseudocapacitance)'''<br/> 6. Solvent molecule.]] |
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[[File:Supercapacitors-Short-Overview.png|thumb|center|300px|Hierarchical classification of supercapacitors and related types]] |
[[File:Supercapacitors-Short-Overview.png|thumb|center|300px|Hierarchical classification of supercapacitors and related types]] |
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Revision as of 15:03, 8 January 2013
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], coined a pseudocapacitance.
A pseudocapacitor is part of an electrochemical capacitor, and forms together with an electric double-layer capacitor (EDLC) to create a supercapacitor.
Unlike EDLCs where the electrical charge storage is statically in the Helmholtz double-layers and enhanced by ionic migration between the electrodes without any interaction between the electrode and the ions, a pseudocapacitor does have a chemical reaction at the electrode. A typical reaction is a redox reaction where the ion is O2+ and during charging at one electrode there is a reduction reaction and the other electrode an oxidation reaction. In discharging the reaction is reversed having and the ions move in the other direction across the electrolyte.
Unlike batteries the faradaic electron charge-transfer of the pseudocapacitance in a supercapacitor the ions simply cling to the atomic structure of an electrode. This faradaic energy storing only with fast redox reactions makes charging and discharging of supercapacitors much faster than batteries.
Double-layer capacitance and pseudocapacitance 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 surface of the electrode.
References
- ^ B. E. Conway (1999), [[1], p. 1, at Google Books Electrochemical Supercapacitors: Scientific Fundamentals and Technological Applications], Berlin: Springer, pp. 1–8, ISBN 0306457369
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value (help) See also Brian E. Conway in Electrochemistry Encyclopedia: ELECTROCHEMICAL CAPACITORS Their Nature, Function, and Applications - ^ Marin S. Halper, James C. Ellenbogen, Supercapacitors: A Brief Overview, MITRE, March 2006 [2]