High double-layer capacitance, electrolyte materials

High double-layer capacitance. The capacitance C of a capacitor is proportional to the capacitance of an electrode, which is dependent on the type of electrolyte material chosen. An electrolyte material showing a high double-layer capacitance Cd for a given electrode is desired. 

High r factors are, however, not without some other complications since they imply porosity of materials. Porosity can lead to the following difficulties (a) impediment to disengagement of evolved gases or of diffusion of elec-trochemically consumable gases (as in fuel-cell electrodes 7i2) (b) expulsion of electrolyte from pores on gas evolution and (c) internal current distribution effects associated with pore resistance or interparticle resistance effects that can lead to anomalously high Tafel slopes (132, 477) and (d) difficulties in the use of impedance measurements for characterizing adsorption and the double-layer capacitance behavior of such materials. On the other hand, it is possible that finely porous materials, such as Raney nickels, can develop special catalytic properties associated with small atomic metal cluster structures, as known from the unusual catalytic activities of such synthetically produced polyatomic metal clusters (133). 

The EDLCs store charge electrostatically by using reversible adsorption of ions of the electrolyte on to high specific surface area materials, usually activated carbons. The charge separation occurs on polarisation at the electrode-electrolyte interface, which was first described by Helmholtz in 1853 as double layer capacitance. This is mathematically defined as ... 

Electrode impedance is an important parameter while fabricating the microelecffode array. Lower impedance is generally favoured for the stimulation material which enables high charge transfer capabilities. Looking closer to the elecffode-electrolyte interface the electrode impedance is dominated by the double-layer capacitance (Cd) as explained earlier, which is in series with the resistance of the electrolyte (Rg) [43], This acts like a high-pass filter with a cut-off frequency at ... 

The semicircle at the high frequency region and the spike at the low frequency region are attributed to the bulk material and double layer capacitance at the electrolyte-electrode interface, respectively. The semicircle was found to diminish with temperature increment. On the other hand, the spike becomes more prominent as the temperature rises. This may be due to the ions moving to the electrolyte-electrode interface as temperature increases. 

For both materials, the PEIS spectra show a high frequency semicircle which according to Thomas et al. (Ref (Thomas, Bruce, and Goodenough 1985)) may be associated with charge transfer resistances between the electrolyte and the particles, and double-layer capacitance. They exhibit a high frequency ending at a purely real value of about 10 Q which can be... 

The electric double-layer capacitance is almost linear to the accessible surface area of the electrolyte ions. Additionally, the chemically/electrochemically stability, electric conductivity, and adequate commercial price are necessary for the EDLC electrode, so the activated carbons are suitable as practical electrode materials. The EDLC has been commercialized as a memory back-up device since the 1970s because of its high cycle efficiency and its long cycle life. Recently, the EDLC is also being considered to be one of the promising systems for... 

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]. 

---