Facile synthesis of biomass-derived hierarchical porous carbon microbeads for supercapacitors

Using the facile method of solvent evaporation, the leonardite fulvic acids (LFA)-based porous carbon microbeads (PCM) have been successfully prepared at ambient pressure, followed by carbonization and KOH activation (a low mass ratio alkali/LFA = 1.5) in an inert atmosphere. The effects of KOH treatment on pore structures and the formation mechanism of the PCM were discussed. The results showed that the sample exhibited remarkable improvement in textural properties. The activated carbon microbeads had high surface area (2269 m2 g−1), large pore volume (1.97 cm3 g−1), and displayed excellent capacitive performances, compared with carbon powder. The porous carbon material electrodes with the “porous core structure” behaved superiorly at a specific capacitance of 320 F g−1 at a current density of 0.05 A g−1 in 6 M KOH electrolyte, which could still remain 193 F g−1 when the current density increased to 100 A g−1. Remarkably, in the 1 M TEABF4/PC electrolyte, the PCM samples could reach 156 F g−1 at 0.05 A g−1, possess an outstanding energy density of 39.50 Wh kg−1, and maintain at 22.05 Wh kg−1 even when the power density rose up to 5880 W kg−1. The balance of structural characteristic and high performance makes the porous carbon microbeads a competitive and promising supercapacitor electrode material.