Separating Faradaic and Non-Faradaic Charge Storage Contributions in Activated Carbon Electrochemical Capacitors Using Electrochemical Methods: I. Step Potential Electrochemical Spectroscopy

Development of an electrochemical method for separating the contributions made by faradaic and non-faradaic processes to the total specific capacitance of an electrochemical capacitor electrode is reported. The method is based on step potential electrochemical spectroscopy (SPECS), and its application is demonstrated on activated carbon electrodes in aqueous media. The method involves applying a sequence of small potential steps (±25 mV) across the electrochemical window of the electrode material, with sufficient rest time between steps to allow for current equilibration. Modelling of the resultant i-t data using combined resistive, capacitive, diffusional and residual current terms allows for separation of the faradaic and non-faradaic terms. The behavior of these contributions across the electrode potential window is reported and discussed in comparison with conventional methods of electrochemical analysis, such as cyclic voltammetry.