Ionic transport in pores in activated carbons for EDLCs

The transport properties and morphology of an activated carbon containing macro-, meso-, and micropores were studied and compared to a sophisticated fully nanoporous carbon that almost lacks meso- and macropores. The morphology of the activated carbon was studied using nitrogen adsorption methods and the pore size distribution was investigated using Barret, Joyner, and Halenda and density functional theory models. The transport properties were studied using a microelectrode technique that allows for determination of the effective diffusivity, D-eff. For the meso/macroporous carbon the effective diffusivity was determined using potential step experiments and analysis for both Cottrell and filling diffusivities were made. The Cottrell diffusivity was smaller than the value of the filling diffusivity, with mean values of (9.4 +/- 3.8) x 10(-14) m(2) s(-1) and (3.1 +/- 1.6) x 10(-12) m(2) s(-1), respectively. This difference in diffusivities is the basis for an agglomerate hypothesis presented for the meso/macroporous carbon. The results for the meso/macroporous carbon are compared with the corresponding results for the sophisticated fully nanoporous carbon. This gave further evidence for the presented agglomerate hypothesis. (c) 2006 The Electrochemical Society.