Microwave synthesis of hierarchically porous activated carbon from lignite for high performance supercapacitors

Abstract

A hierarchically porous activated carbon (HPAC) with high surface area (3064 m2/g) and large pore volume (2.319 cm3/g) was prepared from lignite using KOH as activation agent by microwave heating. Nitrogen adsorption–desorption at −196 °C, X-ray diffraction, scanning electron microscope, transmission electron microscope and X-ray photoelectron spectroscopy were used to characterize the HPAC. Because of its high surface area, macro–meso–micro hierarchically porous structure and oxygen-enriched surface, the HPAC exhibits excellent electrochemical performance in terms of specific capacitance, energy density and cycling stability as electrode material for supercapacitors. The HPAC showed a high specific capacitance of 390 F/g in aqueous electrolyte at a current density of 50 mA/g and 94.1 % of the initial specific capacitance was retained after 2000 cycles. Furthermore, this HPAC displayed a high specific capacitance of 198 F/g in an organic electrolyte.