Carbon materials for the electrochemical storage of energy in capacitors

The electrochemical storage of energy in various carbon materials (activate d carbons, aerogels, xerogels, nanostructures) used as capacitor electrodes is considered. Different types of capacitors with a pure electrostatic att raction and/or pseudocapacitance effects are presented. Their performance i n various electrolytes is studied taking into account the different range o f operating voltage (1 V for aqueous and 3 V for aprotic solutions). Trials are undertaken for estimating the role of micro and mesopores during charg ing the electrical double layer in both kinds of electrolytic solutions for which the electrical conductivity and the size of solvated ions art: diffe rent. 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 proper ties due to the Faradaic redox reactions of their rich surface functionalit y. 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 far adaic pseudocapacitance effects. Evaluation of capacitor performance by dif ferent techniques, e.g, voltammetry, impedance spectroscopy, charge/dischar ge characteristics is also discussed. (C) 2001 Elsevier Science Ltd. All ri ghts reserved.