Capacitance control of carbon aerogel electrodes

Carbon aerogels are promising materials as electrodes for capacitive deionization (CDI) units and electrical double layer capacitors (EDLCs). An optimum process is presented for synthesis of nanoporous carbon aerogels via pyrolyzing resorcinol-formaldehyde (RF) organic aerogels, which could be cost-effectively manufactured from RF wet gels by a modified ambient drying technique using acetone exchange/controlled evaporation instead of conventional supercritical drying. The linear shrinkage of RF aerogel during ambient-drying of wet gels was controlled to be less than 4%, almost same as that of supercritical drying. Carbon aerogels obtained by pyrolyzing of RF aerogels (specific surface area 300-400 m(2)/g) retains high specific surface area (400-700 m(2)/g), low density (0.40-1.16 g/cm(3)), and ultrafine pore size (<50 nm) depending on the pH 3.0-6.5 range of the starting RF solution. The specific capacitance of carbon aerogel electrodes activated at 450degreesC in air environment for 1 h has been improved to 220 F/g. (C) 2004 Elsevier B.V. All rights reserved.