The aim of this study is to observe the effects of electrolyte cation on the electrochemical performance of anodic electrode in electrochemical capacitor. In an ideal electrochemical capacitor, the symmetrical anodic and cathodic electrodes have the same contribution to overall cell performances. However, the performance of anodic and cathodic electrodes is dependent on the size of electrolyte cations and anions which are adsorbed at the surface of electrodes. Hence, there would be a deviation in anodic and cathodic potential due to diffusion of ions with different characteristics into the electrode materials.

In this study, each electrochemical cell has been made of two symmetrical activated carbon (AC) electrodes with the same mass of active material on each electrode. The AC electrochemical cells have been tested in organic electrolytes with the same anion and different cations, using cycling voltammetry (CV) at 25 mV/s sweep rate. This was followed by the step potential electrochemical spectroscopy (SPECS) experiment with a 10 mV potential step and 300 s equilibration time. SPECS method is based on applying a series of equal magnitude potential steps on a working electrode, with sufficient rest time to allow for equilibrium to be established for each step throughout an applied potential window [1]. At the same time, the open circuit potential (OCP) of both electrodes have been measured with respect to Ag/AgNO₃ reference electrode during the CV and SPECS experiments. This technique allows us to see how an individual electrode behaves in overall cell performances.

The outcome of this work indicates the shift between the anodic and cathodic potential in all different electrolytes. It was found that, the cathodic potential is more shifted towards the anodic electrode which means that during charging process more anions are adsorbed at the surface of the cathodic electrode so it covers a larger potential window than the anodic electrode.

Additionally, the specific capacitance obtained by the SPECS method was used to obtain the performance of the AC electrochemical cell in non-aqueous electrolytes with different cations in the form of a Ragone diagram.

[1]. Marveh Forghani and Scott W. Donne, Journal of the Electrochemical Society 2018 165: A664-A673.