Nanoporous carbon synthesised with coal tar pitch and its capacitive performance

Abstract

Nanoporous carbon was prepared by the oxidation of coal tar pitch in a mixture of HNO₃–H₂SO₄ and simultaneous KOH activation with carbonisation at 800 °C. Its capacitive performance was studied by constructing symmetric and asymmetric capacitors. In symmetric supercapacitors in which a 6 M KOH solution was used as an aqueous electrolyte, the synthesised nanoporous carbon possessed a capacitance of more than 160 F g⁻¹ when operating at a current density of up to 100 A g⁻¹. The present process via oxidation from the pitch produced minute particles with a size of approximately 250 nm × 10 nm and abundant oxygen content, which could be efficiently activated using relatively small amounts of KOH. The use of KOH at a concentration of 1.5 times that of the carbon precursor resulted in a high BET surface area of 2600 m² g⁻¹ and a micro- and meso-pore network that was most likely to be highly connected. The asymmetric capacitor of the synthesised nanoporous carbon and hollow MnO₂ microcubes could be charged and discharged reversibly within a potential range of 0.0–2.0 V when a 1 M Na₂SO₄ solution was used as the aqueous electrolyte, delivering an energy density of 30 W h kg⁻¹ at a power density of 0.15 kW kg⁻¹ and preserving an energy density of 13 W h kg⁻¹ even at a higher power density of 30 kW kg⁻¹.