The interfacial surface of an electrode for a supercapacitor as a factor affecting the capacitance and energy density

The present paper proposes a criterion-based approach for selecting carbon material for supercapacitors, which is based on the type of surface functional groups and the micro/mesopore ratio. The activated carbons DLC Supra 30, W35, SX1G and CAP Super WJ (Cabot Corp.) with different porous structure and surface composition have been used as model objects. The BJH, DFT and t-plot methods have been used to calculate the specific surface area and the porosity of activated carbons, characterizing them as micro- and mesoporous materials with a surface area from 845 to 1855 m2·g−1. The SEM micrographs of electrodes allowed estimating the size and agglomeration degree of carbon particles and width of pores on surface. The combined results of FTIR spectroscopy and Boehm titration showed the presence of phenolic, carbonyl and carboxyl functional groups on the surface, the concentration of which depended on the activated carbon grade. By comparing these results with the data of cyclic voltammetry, the influence of the micro/mesopore surface area ratio on the specific capacitance was established. Also, a correlation between the ionic character of the functional groups and the value of energy density has been noted. The results obtained by these methods can serve as a criterion for choosing the activated carbon as an electrode material for supercapacitors.