Hierarchical porous carbon derived from carboxylated coal-tar pitch for electrical double-layer capacitors

Abstract

Hierarchical porous carbons have been synthesized using amphiphilic carboxylated coal-tar pitch as a precursor via a simple KOH activation process. Amphiphilic carboxylated coal-tar pitch has a high content of hydrophilic carboxyl groups that enable it to be easily wetted in KOH solution and that facilitate the activation process. In the present study, the effect of the activation agent to precursor ratio on the porosity and the specific surface area was studied by nitrogen adsorption–desorption. A maximum specific surface area of 2669.1 m² g⁻¹ was achieved with a KOH to carboxylated pitch ratio of three and this produced a structure with micropores/mesopores. Among the various hierarchical porous carbons, the sample prepared with an activation agent to precursor ratio of two exhibited the best electrochemical performance as an electrode for an electrical double-layer capacitor in a 6 M KOH electrolyte. The specific capacitance of the sample was 286 F g⁻¹ at a current density of 2 A g⁻¹ and it had a capacitance-retention ratio of 93.9%, even after 10 000 cycles. Thus, hierarchical porous carbons derived from amphiphilic-carboxylated coal-tar pitch represent a promising electrode material for electrical double-layer capacitors.