Effect of Functional Groups on EDLC Characteristics

These surface groups are considered less stable and include such groups as carboxyl, lactonic, and phenol ones. Basic and neutral surface oxides are considered to be more stable than acidic oxides and tend to contact oxygen at low temperatures. Functional groups that are electrochemically inert in the range of working potentials can cause an increase in the wettability of carbon electrodes and therefore enhance specific capacitance of carbon by improving access of aqueous electrolytes to pores that results in better use of the surface. 

After electrochemical oxidation of graphite, the concentration of strong and weak acidic groups on its surface increases, which was confirmed using the titration technique. Electrochemical preoxidation results in an increase in the capacitance of graphite and ACC. Impedance measurements were used to calculate capacitance 160 F/g for electrodes without oxidation and 220 F/g for electrodes after oxidation. An additional contribution into the overall capacitance is because of pseudocapacitance of redox reactions of surface groups. 

At the same time, surface functional groups contribute to the main capacitance under charge accumulation on carbon electrodes they can charge and discharge fast and result in a significant increase in pseudocapacitance. 

Electrochemical pretreatment of activated carbon fibers (ACEs) based on polyacrylonitrile (PAN-based) in a NaN03 solution resulted in an increase in the content of oxygen-containing functional groups in the fiber surface and therefore led to an increase in specific capacitance Cg. ACEs oxidized for 6h contained 1.3mmol/g of O and Co was formed on 76% of them under thermal treatment. Various carbon materials, including anthracite and different carbon fibers, were activated by KOH, NaOH, CO2, or water vapor at 650-750 C. The values of Cg measured for all carbon 

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