Deconvolution of electrochemical double layer capacitance between fractions of active and total surface area of graphite felts

The electrochemical double layer capacitance (EDLC) of untreated and thermally-activated polyacrylonitrile based carbon felts is correlated with their active surface area (ASA), consisting of edge planes and defects, and the amount of basal planes, which can be calculated from the difference between total and active surface area (TSA-ASA). The ASA was estimated by oxygen chemisorption and desorption and TSA according to BET with Kr. The gravimetric capacitance of the felts was determined by cyclic voltammograms and electrochemical impedance spectroscopy in sulphuric acid and the influence of pseudo-capacitance on EDLC is minimized by choosing a specific, limited potential range. Under this constraint a simple method of deconvolution is applicable, which allows to calculate EDLC from ASA and TSA. The estimated specific capacitances for edge and basal planes of the felts, agreed well with literature values for highly oriented pyrolytic graphite. Therefore, carbon felts can be considered as an ensemble of mainly exposed basal planes with a lower fraction (max. 17% for our study) of edge planes and defects.