The Effect of Surfactants on Double-Layer Capacitance Induced by Electric Fields

Abstract

The wettability of the interface between a solution and an electrode has a significant impact on the improvement of the capacitance behavior of an electric double layer (EDL), especially in water-based carbon electrode supercapacitors. In this paper, we demonstrate the effect of surfactants on the capacitance behavior of an EDL induced by an electric field. The chronopotetiometry method is used to measure the electrochemical model of a carbon electrode in an KCl aqueous solution. It is found that the concentration of the sodium dodecyl sulfate (SDS) surfactant below the critical micelle concentration (cmc) has a positive correlation with the increase in the EDL capacitance, but exceeding the cmc will reduce the measured value of the EDL capacitance. This may be attributed to the influence of surfactants on the orientation of the solvent dipoles on the electrode surface with various micelle states. In addition, we selected different carbon chain lengths of SDS to study the variation of EDL capacitance and the ratio of dipole moment; the effect of the length of the carbon chain on the dipole moment ratio and EDL capacitance shows an increase when the number of carbon atoms is less than 12 and then gradually decreases with the increase of the carbon atoms.