Supercapacitor carbon electrodes

For supercapacitor carbon electrodes, it will be further shown that (1) the developed surface area is responsible of an important electrical double-layer capacitance (2) both the oxygenated and nitrogenated functionalities may be involved in redox reactions with the electrolyte, which enhance capacitance through a pseudo-capacitive contribution. 

A classic definition of electrochemical ultracapacitors or supercapacitors summarizes them as devices, which store electrical energy via charge in the electrical double layer, mainly by electrostatic forces, without phase transformation in the electrode materials. Most commercially available capacitors consist of two high surface area carbon electrodes with graphitic or soot-like material as electrical conductivity enhancement additives. Chapter 1 of this volume contains seven papers with overview presentations, and development reports, as related to new carbon materials for this emerging segment of the energy market. 

In the last paper, A. Lewandowski et al. of Poland, examines the role of ionic liquids as new electrolytes for carbon-based supercapacitors. Although not directly addressing the role of new carbon materials (the area of major focus of this book), this interesting theoretical work seeks to optimize electrolyte media, which is in contact with carbon electrodes. 

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.). 

Solid ionic conductors can also be used in the fabrication of solid state double-layer supercapacitors. An example is the device developed in the late 1960s by Gould Ionics which adopted a cell system using a silver-carbon electrode couple separated by the highly ionically conducting solid electrolyte RbAg4I5 (see Section 9.1) ... 

In recent years there has been increasing interest in the power capacitors, ultracapacitors or supercapacitors based on electrochemical systems. These include electric double layer capacitor (EDLC) types based on carbon electrodes with suitable electrolyte systems, and electrochemical capacitors with pseudocapacitance [34,35],... 

In the past five years, many ion conducting polymers and gel electrolytes have been investigated for EDLC application. Figure 15 shows the capacities of various carbon electrodes in SPE or gel electrolytes. The values listed in this figure do not satisfy the requirements for EV. However, it is expected that the requirements of supercapacitors for EV can be achieved by development of devices based on composite electrodes and gel electrolyte systems as described in this chapter. 

The capacitance of carbon electrodes in acidic and alkaline solutions is quite high, yet the narrow electrochemical window of aqueous solutions is a main disadvantage when used in supercapacitors. Hence, it is possible to increase the -> energy density of supercapacitors by enlarging their working potential window. For that, polar aprotic solutions can be suitable. Indeed, many apro-... 

An example of the effects of the stabihty of carbon chemistry is its impact on the electrochemical performance of carbon electrodes, which is altered by the presence of surface groups [1-3]. Now that the use of carbons as supercapacitors for energy storage has begun to attract interest [4-6], some attention has been devoted to the influence of the surface chemistry of these materials on their capacitance. It was found that surface functionality has a tremendous effect on the electrical double-layer properties and the capacity of the latter for energy storage [7-9]. 

Obreja, V. V On the performance of supercapacitors with electrodes based on carbon nanotubes and carbon activated material—a review. Physica E Low-dimensional Systems and Nanostructures. 2008, 40(7), 2596—2605. 

J. Fang, M. Cui, H. Lu, Z. Zhang, Y. Lai, and J. Li, Hybrid supercapacitor based on polyaniline doped with lithium salt and activated carbon electrodes, J. Cent. South Univ. TechnoL, 16, 434 39 (2009b... 

DEM 13] Demarconnay L., Calvo E.G., TIMPERMAN L., et al, Optimizing the performance of supercapacitors based on carbon electrodes and protic ionic liquids as electrolytes , Electrochimica Acta, vol. 108, pp. 361—368, 2013. 

Liu, B., Shioyama, H., Jiang, H., Zhang, X., Xu, Q., 2010a. Metal-organic framework (MOF) as a template for syntheses of nanoporous carbons as electrode materials for supercapacitor. Carbon 48,456-463. 

In addition to the ability to generate high power, there is another cause to consider supercapacitors for particular applications, namely, that they are characterized by high stability and high cycling times. This is especially true as regards supercapacitors based on carbon electrodes. Most secondary (rechargeable) batteries if left... 

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