Electrochemical double layer capacitors (EDLCs) store the charge by reversible adsorption of ions at the electrode/electrolyte interface. The optimization of EDLC performance needs to push further our basic understanding of the ion fluxes that occur during the charging/discharging process. Microporous carbon has been widely used as supercapacitor electrode material thanks to their tunable porosity and high specific surface area. However, most of the porous carbon materials have complex carbon structures, so that the mechanism is still poorly understood.

Using electrochemical quartz crystal microbalance technique (EQCM) technique, we studied the charge storage mechanisms of two nanoporous carbide-derived carbon (TiC-CDC) electrodes, namely CDC-800 synthesized at 800℃ and CDC-1100 synthesized at 1100℃. These two carbons have a similar porosity but the CDC-1100 sample shows more graphitic carbon microstructure. We found that a counter-ion adsorption process mainly controls the charging mechanism of CDC-800 (“V” shape m vs Q plot), while an expanded ion-exchange and counter-ion adsorption process is obtained for CDC-1100 (“U” shape). We show here that the local carbon structure affects the charging mechanism of electrical double layer capacitance, and a strong interaction between the anions and graphitic carbons explains these different behaviors. Our results provide more insights into the fundamental understanding of the carbon/electrolyte interface and the charge of the electrical double layer capacitance.

Figure 1. Electrode mass change versus charge during the polarization of CDC-800 (a) and CDC-1100 (b) coated Au electrodes in 2M EMI-TFSI/ACN electrolyte at the scan rate of 10 mV·s⁻¹.