Liquefaction pitch-based porous carbon: Preparation and relationship between pore structure and electrochemical properties

Abstract

Coal liquefaction pitch is a byproduct rich in polycyclic aromatic hydrocarbon generated during coal liquefaction process, and can be used to prepare porous carbon electrodes for electric double-layer capacitors. However, the effects of the proportion of pore volume in different pore size ranges on the electrochemical properties of porous carbon are still not well investigated. Herein, porous carbon was fabricated from liquefaction pitch and KOH at a mass ratio of 1:2 and activation temperatures of 600–900 °C. The results showed an increase in both specific surface area and total pore volume of the samples with the activation temperature, inconsistent with the changing trend of the specific capacitances due to well-stored electrolyte ions in micropores. In particular, micropores with pore volume diameter below 1 nm greatly impacted the specific capacitance performance of porous carbon. The pore volume with pore width below 1 nm first increased and then decreased with the activation temperature. Among samples, porous carbon prepared at activation temperature of 700 °C delivered the highest specific capacitance of 329 F g−1 at a specific current of 0.5 A g−1, and retained 254 F g−1 of specific capacitance at 20 A g−1 in 6 mol L−1 KOH electrolyte. The reason for this was related to the largest pore volume with pore width below 1 nm (0.43 cm3 g−1). Afterward, the optimized sample was assembled into a symmetrical supercapacitor and test results showed that 96.37% of the initial capacitance was retained after 10,000 cycles at 1 A g−1, suggesting good cycling stability. In sum, the as-prepared porous carbon is very promising for use as electrode material for supercapacitors.