Kinetics of double-layer charging/discharging of the activated carbon fiber cloth electrode: effects of pore length distribution and solution resistance

The effects of pore length distribution (PLD) and solution resistance R-sol, on the kinetics of double-layer charging/discharging of the activated carbon fiber cloth electrode (ACFCE) were investigated in a 30 wt% H2SO4 solution using nitrogen gas adsorption, a.c. impedance spectroscopy, the current transient technique, and cyclic voltammetry. The impedance spectra of the ACFCE were theoretically calculated based upon the transmission line model in consideration of the pore size distribution (PSD) and the PLD. From comparison of both the experimental and theoretical impedance spectra of the ACFCE, it is suggested that the deviation from the ideal impedance behavior of a cylindrical pore in the experimental impedance spectrum of the ACFCE is mainly ascribed to PLD, rather than to PSD. The cathodic current transients and cyclic voltammograrns were theoretically calculated based upon the transmission line model as functions of the standard deviation of the PLD and Rsol. From the results, it is concluded that ion penetration into the pores is closely related to both u and R-sol, during double-layer charging/discharging of the ACFCE, that is, the larger sigma and R-sol, the lower is the rate capability, thus causing higher retardation of ion penetration into the pores.