Modeling of electrochemical capacitors under dynamical cycling

The electric responses of electrochemical capacitors produced with electrodes build up of reduced graphene oxide (rGO) deposited on Fluorine-doped tin oxide (FTO) coated glass have been experimentally investigated by cyclic voltammetry measurements. According to our experimental data, the parametric curve of the current in the circuit versus the external voltage is a continuous curve without discontinuity points respect to the inversion points of the external voltage. A few equivalent electric circuits able to reproduce the electric response of the capacitor are discussed. The dependence of the area delimited by the parametric cyclic voltammetry curve on the elements of the circuit is investigated. The possible evaluation of the effective capacitance of the capacitor by the numerical evaluation of the area delimited by the parametric curve is critically discussed and the limit of the procedure is underlined. A model based on the Poisson-Nernst-Planck theory with adsorbing electrodes is developed and used to fit the experimental voltammogram. The agreement between the theoretical model and the experimental data is good, indicating the importance of the adsorption phenomenon in the electric response of electrochemical capacitor to an external electric field.