Carbon materials for the electrochemical storage of energy in capacitors Review Article

The electrochemical storage of energy in various carbon materials (activated carbons, aerogels, xerogels, nanostructures) used as capacitor electrodes is considered. Different types of capacitors with a pure electrostatic attraction and/or pseudocapacitance effects are presented. Their performance in various electrolytes is studied taking into account the different range of operating voltage (1 V for aqueous and 3 V for aprotic solutions). Trials are undertaken for estimating the role of micro and mesopores during charging the electrical double layer in both kinds of electrolytic solutions for which the electrical conductivity and the size of solvated ions are different. The effect of pseudocapacitance for maximising the total capacitance is especially documented. Carbons chemically modified by a strong oxidation treatment represent a very well defined region of pseudocapacitance properties due to the Faradaic redox reactions of their rich surface functionality. Conducting polymers (polyaniline, polypyrrole, polythiophene derivatives) and oxidised metallic particles (Ru, Mn, Co,…) deposited on the carbons also participate in the enhancement of the final capacity through fast faradaic pseudocapacitance effects. Evaluation of capacitor performance by different techniques, e.g. voltammetry, impedance spectroscopy, charge/discharge characteristics is also discussed.