A novel model electrode for investigating ion transport inside pores in an electrical double-layer capacitor: Monodispered microporous starburst carbon spheres

Model electrodes were prepared from monodispered microporous starburst carbon spheres obtained by nanocasting route using monodispersed mesoporous silica spheres as a template. The obtained starburst carbon particles had different particle diameter (510-1000 nm) with the same surface area of 1700 m(2) g(-1) and a pore size of 1.2 nm. The effect of effective pore length, which is regarded as the particle diameter in this study, and the electrode thickness on the ion diffusive resistance of electrical double-layer capacitors has been separately investigated. Electrochemical impedance spectroscopy was employed to evaluate the length of the 45 degrees Warburg region in the Nyquist plot, which relates to the equivalent distributed resistance in the porous structure of the electrode. For electrodes with constant thickness of 200 mu m an increase of the ion transport resistance was observed with increasing particle diameter. On the other hand, for constant particle diameter the resistance increases with increasing electrode thickness. Using the starburst microporous carbon spheres as electrode active materials, the contribution of the particle's micropores and of the macropores between the particles can be clearly distinguished. The influence of the effective pore length of carbon particles on the transport of ions within the pores is directly evaluated for the first time. (c) 2012 Elsevier Ltd. All rights reserved.