Abstract
A double layer capacitance (DLC) has mainly been brought about in the Helmholtz layer rather than in the diffuse layer, as was demonstrated with the invariance of DLC to salt concentration, c, less than 0.5 M (M = mol dm−3). The DLC measured here increased with concentrations of KCl and HCl solutions as high as 1 M at a platinum electrode by the ac impedance method. It was represented as a sum of the Helmholtz capacitance and the ionic one which had 0.7 power of the concentrations. The simple addition implies that the Helmholtz contribution and the ionic one should be represented by a parallel combination rather than a series one such as in the Stern model. The disagreement of the experimental values of the DLC with the Gouy–Chapman theory at high concentrations has been conventionally attributed to the effects of packing of ions over their sizes. In this paper, a model of avoiding the packing was introduced, in which ions were distributed in the direction normal to the electrode in the balance of electric motive force and the thermal energy, keeping the uniform distribution on a plane projected to the electrode. The energy balance was taken by using the grand canonical ensemble in statistical mechanics. The ionic contribution had a linear relation with the applied voltage rather than exponential dependence. When a series combination was applied to the Helmholtz capacitance and the ionic one under the condition of difference between the locally anionic DLC and the cationic one, we obtained approximately a parallel combination of the two capacitances because either the anionic or the cationic DLC works predominantly.
Highlights
The development of double layer capacitance (DLC) as an electric energy storage has focused [1,2] on the enhancement of the output energy, the power, and cycle stability
We show here the concentration- and voltage-dependence of the DLC including frequency-dispersion obtained by ac-impedance at a platinum wire in KCl and HCl solutions
The DLC at platinum electrode in KCl and HCl solutions can be represented as a simple sum of the Helmholtz capacitance and the ionic contribution
Summary
The development of double layer capacitance (DLC) as an electric energy storage has focused [1,2] on the enhancement of the output energy, the power, and cycle stability. Industrial improvements have been conceptually directed [3,4] towards: (a) the geometric feature of electrodes such as the enhancement of specific surface areas, (b) solutions to increase ionic conductance, and (c) an increase in applied voltages. Inactive electrodes and solutions with widely depolarized voltage domains have been searched tentatively in order to enhance the energetic performance with the square of the applied voltage [7,8]. These improvement techniques have been used on an empirical basis rather than thermodynamic theory
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
