Contributions of storage sites located in micro- and meso/macropores to the capacitance of carbonaceous double layer capacitor electrodes

To investigate the contributions of charge storage sites located in micro- and meso/macropores, respectively, to the electrochemical double layer capacitance in carbon electrodes, a series of monolithic (non-activated) carbon aerogel electrodes was synthesized. The major feature of the prepared model materials is their systematic variation with respect to surface area located in micro- and meso/macropores. For comparison, selected samples of the electrode series were activated using thermal treatment in CO2. Structural characterization of all electrodes was performed by scanning electron microscopy and gas adsorption analysis utilizing density functional theory and t-plot method. Cyclic voltammetry in aqueous KCl-solution (1 M) was performed to determine the samples' gravimetric capacitance for different voltage windows (0.2-1.8 V) and scan rates (10, 1, 0.1 mV/s). The capacitance contributions of micro- and meso/macropores normalized to the corresponding surface area were separated using the linear fit method introduced by Shi. The obtained results suggest a steric or energetic limitation of the ion accessibility to small micropores, that is resolved with increasing voltage applied. Contrary, the charge storage sites in meso- and macropores exhibit no such restriction but are accessible in all voltage windows considered. Activation of the samples by CO2 thermal treatment did not lead to a change of these voltage window dependences.