Temperature dependence double-layer capacitance, electrolytic

From their calculations of the surface excess entropy and volume of the electric double layer at a mercury-aqueous electrolyte interface, Hill and Payne (HP) [147] postulated an increase in the number of water molecules in the Stern inner region as the surface charge a of about 30 piC/m2, which is consistent with the results of TC on a silver surface obtained some 30 years later. HP used an indirect method to determine the excess entropy and volume by measuring the dependence on temperature and pressure of the double layer capacitance at the mercury-solution interface. 

The existence of a current hump near Tc is confirmed by several additional facts. In the first place, these are deduced from the results of the quantitative treatment of the impedance spectra of the HTSC/solid electrolyte system [147]. This approach consists of calculating from the experimental complex-plane impedance diagrams the parameters characterizing the solid electrolyte, the polarization resistance of the reaction with the participation of silver, and the double-layer capacitance (Cdi) for each rvalue (measured with an accuracy of up to 0.05°). Temperature dependence of the conductance and capacitance of the solid electrolyte (considered as control parameters) were found to be monotonic, while the similar dependences of two other parameters exhibited anomalies near Tc- The existence of a weakly pronounced minimum of Cji near Tc, which is of great interest in itself, was interpreted by the authors as the result of sharp reconstruction of the interface in the course of superconducting transition [145]. 

The rapid temperature change of the electrode perturbs the equilibrium at the electrode-solution interface and causes a change in the potential of the electrode measured with respect to a reference electrode. The change in the open-circuit potential, A t, and its relaxation with time are used to obtain kinetic information about the electrode reaction. A number of different phenomena come into play to cause the potential shift with temperature (e.g., temperature dependence of the double-layer capacitance and the Soret potential arising from the temperature gradient between the electrode and the bulk electrolyte), but the response can be treated by a general master equation (40) ... 

Reszko-Zygmunt, J., S. Sokolowski, D. Henderson, and D. Boda. 2005. Temperature dependence of the double layer capacitance for the restricted primitive model of an electrolyte solution from a density functional approach. The Journal of Chemical Physics 122 084504. 

The actual value of the double-layer capacitance depends on many variables including electrode type, electrochemical potential, oxide layers, electrode surface heterogeneity, impurity adsorption, media type, temperature, etc. [1, pp. 45-48]. Capacitance of the double layer also largely depends on the intermolecular structure of the analyzed media, such as the dielectric constant (or high-frequency permittivity), concentration and types of conducting species, electron-pair donicity, dipole moment, molecular size, and shape of solvent molecules. Systematic correlation with dielectric constant is lacking and complex, due to ionic interactions in the solution. In ionic aqueous solutions with supporting electrolyte ("supported system") the values of -10-60 pF/ cm are typically experimentally observed for thin double layers and solution permittivity e - 80. The double-layer capacitance values for nonpolar dielec-... 

Figure 17.7 shows the change of the capacitances of the double-layer capacitors using various electrolytes, when operating temperature was varied from 25 to —25°C. The capacitance of all ionic liquids decreased rapidly compared with the 1 M Et3MeNBFVPC due to the increase of internal resistance reflecting the temperature dependence of electrolytic conductivity in Figure 17.4. We have learned that this behavior is a fatal disadvantage of ionic liquids, and that EMIF -2.3HF is the one exception that affords enough capacitance even at —25°C, as reflects its high electrolytic conductivity.

Figure 17.10 Temperature dependences of electrolytic conductivity of a new ionic liquid (a) and capacitance of a double-layer capacitor using the ionic liquid (b).

The discussion about Equations (2.16) and (2.19) shows that the differential capacitance of the double-layer is mainly dependent on the charge (z ), the electrolyte concentration (C°), the solvent used (s,.), and the temperature (T), but does not depend on the types of electrolytes or electrode materials and their structures. It may be true that as long as an electrode is electrically conductive, the differential capacitance should be similar if other conditions are the same. However, if the electrode is a semiconductive material, the net charge accumulated at the electrode will have a diffuse distribution near the interface at the electrode side. 

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