Effects of the mesostructural order on the electrochemical performance of hierarchical micro–mesoporous carbons

Abstract

Hierarchical ordered porous carbons show a better behavior as electric double layer capacitors (EDLCs) than disordered carbons especially at high rates thanks to their unique architectural design. In the present work, we demonstrate that mesostructural order is a key factor for the performance of carbons at high rates. For that, two series of hierarchical micro–mesoporous carbons were prepared by chemical activation with KOH following two different procedures. SBA-15 silica was infiltrated by chemical vapor deposition of propylene and the resulting carbon–silica composite was split into two halves. One part was directly activated and, subsequent to the activation process, the template was eliminated. The second part was first subjected to the template removal and the resulting CMK-3 type carbon was further activated. Thus, carbons obtained by both these methods present bimodal pore size distributions and different mesostructural order as a function of the activation conditions. Carbons prepared from the direct activation of the composite present a high conservation of the ordered mesoporous structure. The electrochemical performance of both carbon series was tested in an acid aqueous electrolyte (1 M H₂SO₄) by cyclic voltammetry and impedance spectroscopy. A highly ordered mesoporous structure significantly improves the specific capacitance at high scan rates due to enhancement in the diffusion of molecules.