Valorization of composting leachate for preparing carbon material to achieve high electrochemical performances for supercapacitor electrode

Composting leachate, a potential precursor, was attempted to prepare the activated carbons via hydrothermal carbonization plus KOH activation in this work. The obtained carbons were further investigated to check their electrochemical performances as electrode materials of supercapacitor. The carbon material that activated at 700 °C (CL-700) exhibits the highest specific surface area of 2184.9 m2 g−1 and the largest pore volume of 1.55 cm3 g−1 comparing to the activated carbons at other temperatures. In a three-electrode system, CL-700 displayed an excellent capacitance of 228 F g−1 at 0. 5 A g−1, and it was 178 F g−1 even though at a higher current density of 10 A g−1. After 5000 tests on the charge-discharge cycle, CL-700 showed a superior stability with 83.2% capacity retention and almost 100% coulombic efficiency at 5 A g−1. Moreover, CL-700 had a good energy density of 7.1 Wh kg−1 at a power density of 124.9 W kg−1 in a symmetric two-electrode system. Based on the comparison with the currently reported biomass-deriver carbons, the composting leachate can be regarded as a feasible precursor to harvest carbon materials for supercapacitor electrode, which was meaningful to offer a novel path for the valorization of the leachate fraction from bio-wastes.