Demonstration of Uninvolvement of Ions for Double Layer Capacitance by Use of Latex Suspensions

Abstract

Water molecules in aqueous solutions were demonstrated to participate in formation of electric double layer capacitance, as partly agrees with the Stern–Gouy–Chapman theory, which is quite different from current fabrication techniques of industrial double layer capacitors. This conclusion was supported firstly by invariance of capacitance to ionic concentrations and secondly by exhibiting the same capacitance values in ionic latex suspensions without free ions as those in conventional ionic solutions. The latex particles used were mono-dispersed polystyrene sulfonic acid, 3.33 μm in diameter. The latex suspension was deionized to show low ionic concentration of less than 0.01 mM. Ac-impedance data were obtained at parallel platinum wires without insulating shield in order to avoid stray capacitance at cracks between electrodes and shields. They were analyzed through the equivalent circuit of a series combination of solution resistance and the double layer impedance. The latter was composed of a parallel combination of the capacitance and resistance, both of which depended on frequency. The solution resistance was inversely proportional to the concentration of the ionic latex particles, whereas the parallel capacitance was independent of the concentrations.