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Polymers for Supercapacitors
Published in Soney C George, Sam John, Sreelakshmi Rajeevan, Polymer Nanocomposites in Supercapacitors, 2023
Sreelakshmi Rajeevan, Sam John, Soney C George
At the initial stage of the development of EDLCs, aqueous solutions are used as electrolytes. Later, the extension of the Helmholtz model introduced non-aqueous and ionic liquids as electrolytes for EDLCs. The charge, concentration of electrolyte, solvent, and temperature are the parameters that directly influence the electrochemical double-layer capacitance. The type and structure of the electrode material and electrolyte have no direct relation to the double-layer capacitance. In reality, differential double-layer capacitance is obtained depending on the surface structure and conductivity of both electrode and electrolyte. For a selected electrode material, the electrolyte with different sizes and morphological specialties has different interactions resulting in different adsorption strengths, and for a selected electrolyte, the mechanism is vice versa. The electrode materials generally used for the fabrication of EDLCs are carbonaceous materials such as activated carbon, graphene, carbon nanotubes, carbon-derived carbon, carbon fiber cloths, carbon organic frameworks (COFs), carbon aerogels, etc. The chosen carbon-based electrode material should be highly conductive, porous, and have a specific surface area between 500 to 4000 m2/g. The discussion regarding carbon-based EDLCs has been given in detail in the coming chapters.
Porous Materials and Electrochemistry
Published in Antonio Doménech-Carbó, Electrochemistry of Porous Materials, 2021
The classical model for describing the electrode-liquid electrolyte junction considers a highly structured region close to the electrode surface, the double-layer with dipole-oriented solvent molecules, and a double layer of charge-separated ions that creates a capacitive effect. At a larger distance from the electrode surface, there is a less structured region—the diffuse layer—that finally reduces to the randomly organized bulk electrolyte solution. The earlier formulation according to Helmholtz distinguishes between the inner (Helmholtz) layer, which comprises all species that are specifically adsorbed on the electrode surface, and the outer (Helmholtz) layer, comprising all ions that are closest to the electrode surface but are not specifically adsorbed [29]. As far as the area and geometry of the electrode surface influence the double-layer capacitance, porous materials with large effective surface areas can yield significant capacitance effects that will be further commented on.
Electrochemical Energy
Published in Prasanth Raghavan, Fatima M. J. Jabeen, Polymer Electrolytes for Energy Storage Devices, 2021
P. P. Abhijith, N. S. Jishnu, Neethu T. M. Balakrishnan, Akhila Das, Jou-Hyeon Ahn, Jabeen Fatima M. J., Prasanth Raghavan
The EDLCs are also like a battery, where there are two electrodes immersed in an electrolyte. During the charging process, the positive electrode attracts anions from the electrolyte and, similarly, the negative electrode attracts cations. However, unlike the batteries, the electrolyte ions do not react with the electrode material [77–80] as shown in Figure 1.8a. For such supercapacitors, the double layer capacitance at each electrode surface can be related to the effective surface area of the electrode and to the effective thickness of the double layer, and can be given by C= εA/d, where ε is the dielectric constant of the double layer and A is the surface area of the electrode. Here, d represents the effective thickness of the double layer. Because of this kind of surface dependence for charge storage, optimization of pore size and structure, surface properties, and conductivity of electrode materials becomes very important.
Effect of novel cryogenic treatment in the corrosion behaviour, microstructure analysis and electrochemical properties of Al 6101 closed-cell foam
Published in Australian Journal of Mechanical Engineering, 2023
Zeenath Fathima Syed, Tamilarasan T.R, Milon Selvam Dennison
The obtained Rct value increases from 966 Ohm to 47,300 Ohm for UT, HT, CT, and CHT zones, respectively. Interesting results are obtained with respect to Al 6101 closed-cell foam in the HT zone. The protection efficiency percentage of Al 6101 Closed-cell foam derived from EIS data are shown in Table 5. The protection efficiency percentage of Al 6101 closed-cell foam derived from potentiodynamic polarisation data is found to be 97.95%, 56.53%,49.28%, for HT, CT, CHT zones, respectively. The obtained results from the Nyquist curves are in good agreement with the polarisation curves in such a way that the Protection Efficiency percentage with respect to untreated foam is higher only in the HT zone when comparing to CT, CHT zones. The formation of a double-layer capacitance depends on electrode potential, temperature, ionic concentrations, type of ions, oxide layers, electrode roughness, and adsorption of impurities. The controlled kinetic reaction causes a charge transfer resistance, and the charge transfer speed depends on the kind of reaction, temperature, the concentration of reaction products and applied potential for a combination of electrolyte resistance.
Experimental and computational investigation of variamine blue as an inhibitor for copper in chloride solution
Published in Journal of Dispersion Science and Technology, 2022
Güray Kılınççeker, Sema Çelik, Farhad Zarifi, Koray Sayın
The corrosion reaction occurs at the metal/solution interface. The actual impedance, the difference between the lowest and highest frequency regions, corresponds to the load transfer resistance. The electrical equivalent circuit formed at the metal-solution interface is shown in Figure 5. Further to Rp, Rct, Rf and RF, solution resistance (Rs) and constant phase element (CPE) instead of the double-layer capacitance were used in fitting process. The value of the double-layer capacitance depends on many variables including electrode potential, temperature, ionic concentrations, types of ions, oxide layers, electrode roughness, impurity adsorption, etc. Table 1 indicates that by increasing the concentration of variamine blue the inhibition efficiency increases. The increase in RP, which results from local dielectric constant decrease and/or an increase in the thickness of the electrical double layer, suggests that these molecules act by adsorption on the metal/solution interface.[28] The degree of surface coverage for different concentrations of these compounds has been evaluated from EIS measurements too.[29] It is clear that RP increases as the inhibitor concentration increases. The increase in RP could be attributed to the adsorption of the inhibitor, forming a protective adsorption layer.[30]
A simplified state-space model for performance analysis of proton exchange membrane fuel cell
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2020
From Figure 2, at light loading condition there is heavy nonlinear potential drop in polarization characteristics of PEMFC, called as activation polarization drop. The activation polarization drop depends on exchange current density and operating temperature of PEMFC. The exchange current density again depends on electrode surface area and catalyst activity. The electrochemical double-layer capacitance (ELDC) formed between electrode and electrolyte also depends on electrode surface area and contact area between electrode and electrolyte. Hence, increase in electrode surface area and contact area between electrode and electrolyte increases numerical value of double layer capacitance. As double layer capacitance and exchange current density both depend on electrode surface area, therefore increase in double layer capacitance increases exchange current density. Increase in exchange current density decreases activation polarization drop, increases terminal voltage and hence increases power density. The effect of double layer capacitance on terminal voltage of PEMFC is shown in Figure 8. For analysis, four different values of capacitances (4 F, 8 F, 42 F, and 48 F) are considered. The decrease in activation polarization drops improves slow dynamics and increase in terminal voltage increases peak power supplying capability of PEMFC.