Preparation, surface characteristics, and electrochemical double-layer capacitance of KOH-activated carbon aerogels and their O- and N-doped derivatives

Abstract

Carbon aerogels are obtained by carbonizing organic aerogels prepared by polycondensation reaction of resorcinol or pyrocatechol with formaldehyde. They are KOH-activated at two KOH/carbon ratios to increase pore volume and surface area. Selected samples are also surface-treated to introduce oxygen and nitrogen functionalities. The objectives are to investigate the effect of porosity and surface functionalities on the electrochemical capacitance of the carbon and activated carbon aerogels. Samples are characterized by N2 and CO2 adsorption at −196 and 0 °C, respectively, immersion calorimetry, temperature-programmed desorption, and X-ray photoelectron spectroscopy in order to determine their surface area, porosity, and surface chemistry. Two series of samples are obtained: one micro-mesoporous and the other basically microporous. A surface area up to 1935 m2 g−1 was obtained after KOH activation. Electrochemical double-layer capacitance was studied by cyclovoltammetry and chronopotentiometry with a three-electrode cell, using Ag/AgCl as reference electrode. Gravimetric capacitance at 0.125 A g−1 is related to N2 adsorption-measured micropore volume and mean size and to particle density. The highest gravimetric capacitance, 220 F g−1, is obtained with two O- and N-doped samples. Volumetric capacitance of 123 F cm−3, double the value generally needed for applications in small-volume systems, is obtained with a largely microporous oxygen-doped activated carbon aerogel.