Correlation of double-layer capacitance with the pore structure of sol-gel derived carbon xerogels

Nine different sol-gel derived carbon xerogels were prepared with different pore structures by varying the carbonization temperature (in flowing N-2) and activation time (in 5% CO2 in N-2) For each of these carbon xerogels, mesopore and micropore size distributions and cumulative surface areas were extracted from a density functional theory analysis. Increasing the carbonization temperature caused a decrease in the number of micropores in the 6 Angstrom range but had little effect on the mesopore size distribution and thus mesopore cumulative surface area. Increasing the CO2 activation time caused an increase in the number of both micro- and mesopores where pores in the 6 Angstrom width range eventually became pores in the 12 Angstrom width range. The electrochemical double-layer capacitance (DLC) of the carbon xerogels was found to correlate well with changes in the pore structure, and it was determined that pores less than about 8 Angstrom in width did not contribute to the DLC. (C) 1999 The Electrochemical Society. S0013-4651(98)12-091-8. All rights reserved.