Relationships between pore size and charge transfer resistance of carbon aerogels for organic electric double-layer capacitor electrodes

Abstract

Carbon aerogels are prepared from polycondensation of resorcinol and formaldehyde using sodium carbonate as a base catalyst while controlling the ratio of resorcinol to catalyst (R/C). Pore size of the carbon aerogel shows a tendency to increase with the R/C ratio because of the low addition reaction rate between two starting materials with a small amount of catalyst. In addition, the pore size of the carbon aerogels strongly affects their charge transfer resistance and their potential use as organic electric double-layer capacitor electrodes. Ionic resistance to facile mobility of electrolyte ions decreases with increasing pore size of the carbon aerogels, while their electronic resistance exhibited the opposite trend with respect to pore size. These compensation effects between ionic resistance and electronic resistance lead to a different optimum pore size of carbon aerogels for EDLC electrodes depending on the applied charge-discharge rate. A carbon aerogel with large pore size is favorable for use in a low-rate charge-discharge process, while one with small pore size have good performance in a high-rate charge-discharge process. Therefore, we suggest that designing an efficient mesoporous carbon material for an EDLC electrode should include significant consideration of its end use, especially the rate employed for the charge-discharge process.