Mass transport and electrolyte accessibility through hexagonally ordered channels of self-assembled mesoporous carbons

Ordered mesoporous carbons have attracted great interest for their potential use to electrodes for electric double layer capacitors. However, it is crucial to develop an electrode such that the active sites within the mesoporous carbons are accessible to electrolyte solution species via facile mass transport through well-defined pores. Here, we investigate the electrolyte accessibility and the effective mass transport for the ordered mesoporous carbons possessing p6mm symmetry, whereas having different mesochannel length, formed by soft-templating self-assembly. Mesoporous carbons were prepared from a thermosetting phenolic resin and a thermally decomposable copolymer template in ethanol/water solutions of different molar ratios. The general evolution of the mesophase follows the trends that are expected based on packing parameters due to swelling of the hydrophobic volume of the copolymer micelles. However, changes in mesochannel length and the degree of long-range order are found to depend on ethanol/water ratio. Electrochemical impedance spectroscopy was used to assess the transport properties. The impedance data clearly demonstrated that the degree of long-range order and channel length can be a dominant factor that determines the transport and the degree to which the equilibrium adsorption sites are accessible. The lengthy mesochannels in well-ordered mesoporous carbon serve as ion-highways and allow for very fast mass transport into the micropores of the channel frameworks. (C) 2012 Elsevier B.V. All rights reserved.