Method Comparison for Deconvoluting Capacitive and Pseudo-Capacitive Contributions to Electrochemical Capacitor Electrode Behavior

Abstract

Several electrochemical methods have been developed to determine the contribution of different charge storage mechanisms, such as via the electrical double layer and diffusion-limited processes, to electrochemical capacitor behavior. This includes using cyclic voltammetry (CV) data at different sweep rates to obtain the relationship between voltammetric current and sweep rate, and also the relationship between voltammetric charge and sweep rate. Step potential electrochemical spectroscopy (SPECS) also has been used to effectively differentiate between different charge storage mechanisms. Herein we compare these three methods experimentally and also discuss their advantages and limitations toward differentiating between different charge storage mechanisms. These methods have been applied to electrolytic manganese dioxide (EMD) in 0.5 M K2SO4 between 0.0-0.8 V (vs SCE). It was found that in all cases, the specific capacitance was decreased by increasing the sweep rate. The capacitance-sweep rate dependence was only found to be accurate in a short range of low sweep rates. Overall there was good agreement between the SPECS and current-sweep rate dependence models over the full range of sweep rates. However, the SPECS method provided more precise information about the kinetic behavior of the electrochemical cell through a full range of sweep rates.