Pseudocapacitor

Family of super capacitors
Super capacitors                                     Double layer capacitors ( electrostatic , Helmholtz layer ) double layer capacitance   Pseudo capacitors ( electrochemically , Faradaysch ) pseudocapacitance                         Hybrid capacitors (electrostatic and electrochemical, Faradaysch) double layer plus pseudo capacitance

Schematic representation of a double layer on an electrode (BMD model).
1. inner Helmholtz layer ( English inner Helmholtz plane , IHP),
2. outer Helmholtz layer ( English outer Helmholtz plane , OHP),
3. diffuse layer,
4. solvated cations ,
5. desolvated and adsorbed anion (redox ion which contributes to the pseudocapacity),
6. Molecules of the electrolyte solvent

A pseudocapacitor is part of an electrochemical capacitor and, together with a double-layer capacitor (EDLC), forms a supercapacitor . The electrical charge of a pseudocapacitor , the electrochemical pseudocapacitance , adds up to the charge of the double-layer capacitor, the static double-layer capacitance to the total capacitance of the supercapacitor. There is no such thing as a pseudocapacitor alone.

Pseudo capacitors store electrical energy by means of reversible redox reactions at suitable electrode of an electrochemical capacitor with a Helmholtz - bilayer . The redox reactions are associated with a Faraday charge exchange from the ions in the electrolyte to the metallically conductive ions in the electrode. Only one electron from a desolvated and adsorbed ion is involved. The adsorbed ion does not form a chemical bond with the electrode. There is only one electron transfer .

Electrochemical pseudocapacitors use electrodes made of metal oxides or conductive polymers , which are suitable for accepting a large amount of charge carriers. The amount of charge stored in a pseudocapacitor is linearly proportional to the applied electrical voltage . The pseudocapacitor in a supercapacitor has, depending on the design of the electrodes, a very different proportion of the total capacitance. The pseudocapacitance of an electrode suitable for this can, for example, be a factor of 100 greater than the double-layer capacitance with the same electrode surface.

In the reversible redox reactions in a pseudocapacitor, no chemical bonds are made or broken, which means that the charging or discharging of the capacitor is significantly faster than with an accumulator, in which more energy is stored with the help of the chemical bonds, but the charging and discharging are also much faster runs much slower.

Individual evidence

1. ↑ Zbigniew Stojek: The Electrical Double Layer and Its Structure . In: Fritz Scholz (Ed.): Electroanalytical Methods: Guide to Experiments and Applications . Springer, Berlin / Heidelberg 2010, ISBN 978-3-642-02914-1 , p. 3-10 ( online ).
2. ^ ^{A b} B. E. Conway: Electrochemical Supercapacitors: Scientific Fundamentals and Technological Applications . Springer, Berlin 1999, ISBN 0-306-45736-9 , pp. 1–8 ( limited preview in Google Book search). See also Brian E. Conway in Electrochemistry Encyclopedia: ELECTROCHEMICAL CAPACITORS Their Nature, Function, and Applications ( April 30, 2012 memento in the Internet Archive ) (accessed December 7, 2015)
3. ↑ ^{a b} Marin S. Halper, James C. Ellenbogen: Supercapacitors: A Brief Overview. (PDF) In: MITER Nanosystems Group. March 2006, accessed on September 16, 2015 .  (last accessed on September 16, 2015)
4. ^ ^{A b} E. Frackowiak, F. Beguin: Carbon Materials For The Electrochemical Storage Of Energy In Capacitors. In: CARBON. 39, 2001, pp. 937-950 ( PDF ) and E. Frackowiak, K. Jurewicz, S. Delpeux, F. Béguin: Nanotubular Materials For Supercapacitors. In: Journal of Power Sources . Volumes 97-98, July 2001, pp. 822-825, doi: 10.1016 / S0378-7753 (01) 00736-4 .
5. ↑ Josie Garthwaite: How ultracapacitors work (and why they fall short). In: Earth2Tech. GigaOM Network, July 12, 2011, accessed April 23, 2013 .