Electrochemical capacitors pseudocapacitors

In the second type of supercapacitor, sometimes termed pseudocapacitors, redox capacitors or electrochemical capacitors, the non-Faradaic doublelayer charging process is accompanied by charge transfer. This Faradaic process must be characterized by extremely fast kinetics in order to allow device operation with high current density discharge pulses. 

In general, two modes of energy storage are combined in electrochemical capacitors (1) the electrostatic attraction between the surface charges and the ions of opposite charge (EDL) and (2) a pseudocapacitive contribution which is related with quick faradic charge transfer reactions between the electrolyte and the electrode [7,8], Whereas the redox process occurs at almost constant potential in an accumulator, the electrode potential varies proportionally to the charge utilized dr/ in a pseudocapacitor, which can be summarized by Equation 8.5 ... 

Pseudocapacitors store charge based on reversible (faradaic) charge transfer reactions with ions in the electrolyte. For example, in a metal oxide (such as RUO2 or I1O2) electrode, charge storage results from a sequence of redox reactions. Electrochemical capacitors (ECs) based on such pseudocapacitive materials will have both faradaic and nonfaradaic contributions. The optimization of both EDLCs and pseudocapacitors depends on understanding how features at the nanoscale (e.g. pore size distribution, crystaUite or particle size) affect ion and electron transport and the fundamental properties of electrochemical interfaces. 

This chapter describes the fundamentals of different kinds of electrochemical capacitors (ESs), including electrical double-layer capacitors (EDLCs), pseudocapacitors, and hybrid ESs. This serves as a foundation for understanding ES science... 

Lian, K., and C. M. Li. 2008. Heteropoly acid electrolytes for double-layer capacitors and pseudocapacitors. Electrochemical and Solid-State Letters 11 A158-A162. 

An electric double-layer capacitor, also known as supercapacitor, pseudocapacitor, electric double layer capacitor (EDLC), supercapacitor or ultracapacitor is an electrochemical capacitor with relatively high energy density. Compared to conventional capacitors the energy density is typically on the order of thousands of times greater than an electrolytic capacitor. In comparison with conventional batteries or fuel cells, EDLCs have lower energy density but a much higher power density. 

Electrochemical capacitors, also referred as supercapacitors or ultracapacitors, store energy using either ion adsorption (electrochemical double-layer capacitors EDLCs) or fast surface redox reactions (pseudocapacitors). In recent years, they have... 

Recently supercapacitors are attracting much attention as new power sources complementary to secondary batteries. The term supercapacitors is used for both electrochemical double-layer capacitors (EDLCs) and pseudocapacitors. The EDLCs are based on the double-layer capacitance at carbon electrodes of high specific areas, while the pseudocapacitors are based on the pseudocapacitance of the films of redox oxides (Ru02, Ir02, etc.) or redox polymers (polypyrrole, polythiophene, etc.). 

FIGURE 1.3 Schematic diagram for (a) electrostatic capacitor, (b) electric double-layer capacitor, (c) pseudocapacitor, and (d) hybrid capacitor. (Zhong, C. et al. 2015. A review of electrolyte materials and compositions for electrochemical supercapacitors. Chemical Society Reviews 44 7484-7539. Reproduced by permission of The Royal Society of Chemistry.)... 

Despite many advances and an outstanding book [1], we are convinced that we have just begun to evaluate this field. Major advances can be expected from new electrolytes, better purification procedures, new electrode materials, and also from capacitors that include very fast electrochemical reactions (pseudocapacitors). Finally the problem of unsymmetrical voltage window deserves more attention. 

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