The electrochemical capacitance of nanoporous carbons in aqueous and ionic liquids

The electrochemical capacitance of porous carbon materials including activated carbon, carbon nanotubes, and carbon gels were investigated. Due to their different porous structures, these carbons showed different capacitive behaviors in aqueous solutions and ionic liquids. It was found that carbon nanotubes, having the largest micropore volume, and the carbon gels with 3D macroporous framework presented the opposite results in charge capacity in the two media. The experimental data showed that microporous materials presented the higher capacitance in aqueous solutions, while macropores were more favorable for improving power and energy properties in ionic liquids owing to the higher operable voltage of the ionic liquids. This may imply that the capacitive performance of a porous material depends more on its matching degree to the applied electrolytes than on its overall pore volume. Carbon materials with ample macropores could be more suitable to be used in ionic liquids to fully exert the energy output for a capacitor. An electrochemical capacitor based on 3D macroporous carbon gels in ionic liquids has been demonstrated to show a specific energy of 58 W h kg(-1), comparable to a commercial battery. (c) 2007 Elsevier B.V. All rights reserved.