Electrical double layer capacitors energy storage mechanism

Typically, a supercapacitor is composed of two electrodes dipped in an electrolyte solution with a suitable separator. It is generally accepted that the energy storage mechanism of supercapacitors can be classified into electrical double layer capacitors (EDLCs) and pseudocapacitors (Fig. 6.1A) (Jost et al., 2014). In EDLCs, the charge storage is based on a reversible ion adsorption from an electrolyte onto electrodes with high specific surface areas to form a double layer structure. The capacitance comes from the pure electrostatic... 

Depending on the charge storage mechanism, supercapacitors can be classified into two types electrical double layer capacitors (EDLC) and pseudocapadtors [108]. EDLCs store and release energy based on the accumulation of charges at the interface between a porous electrode, typicalty a carbonaceous material with high surface area, and the electrotyte. In pseudocapadtors, the mechanisms rely on fast and reversible Faradaic redox reactions at the surface and/or in the bulk. 

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 (Conway, 1991,1995). Several types of capacitors are classihed in Table 1.8 according to their energy storage mechanisms. 

The energy capacity of ECs arises from either double-layer capacitance for electric doublelayer capacitors (EDLCs) or pseudocapacitance for redox capacitors [2, 3]. The energy storage mechanism of EDLCs is based on non-faradic phenomena in electric double layer formed at an electrode/electrolyte interface. In regard to electrode active materials for EDLCs, carbon materials such as activated carbons have been most widely used [4] because of their reasonable cost, good electrical conductivity, and high specific surface area. However, there is a limitation in their specific capacitance the gravimetric capacitance of most carbon materials does not linearly increase with an increase in the specific surface area above 1,200 m g [5]. 

---