Effect of dilution ratio and drying method of resorcinol–formaldehyde carbon gels on their electrocapacitive properties in aqueous and non-aqueous electrolytes

Carbon gels were prepared by carbonization of organic gels from a resorcinol–formaldehyde mixture in the presence of potassium carbonate and with two different dilution ratios. The organic hydrogels were dried under supercritical and subcritical conditions and by lyophilization. After carbonization, the carbon aerogels, xerogels, and cryogels were characterized by N₂ and CO₂ adsorption at −196 and 0 °C, respectively, and by X-ray photoelectron spectroscopy to determine their surface area, porosity, and surface oxygen content. Electrocapacitive properties were studied by cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy in a two-electrode cell in acidic and non-aqueous aprotic electrolytes. Results obtained showed that the gravimetric capacitance from chronopotentiometry increased linearly for both electrolytes with an increase in the micropore volume accessible to N₂ at −196 °C and in the S_BET. In both series of carbon gels, the cryogel had the lowest electrical resistance and fastest discharge time from electrochemical impedance spectroscopy, indicating that lyophilization may generate a pore texture with lesser tortuosity and greater regularity in comparison with the other drying methods.