3D hierarchical porous carbon from fulvic acid biomass for high energy density supercapacitor with high withstanding voltage

Abstract

Biomass-derived porous carbons (BD-PC) have evoked wide attention in the field of supercapacitors. However, the oxygen-containing groups (OFGs) in BD-PC bring a great threat to the structural stability of porous carbons in organic electrolyte at the voltage window higher than 2.7 V. Therefore, it is a worthwhile challenge to construct BD-PC with very-low content of OFGs which can operate stably at the ultrahigh voltage window. Herein, the green and renewable fulvic acid biomass is used as carbon precursor to construct 3D hierarchical porous carbon (HPC) with high yield of 13.3% by KOH activation and annealing method. This HPC presents continuous carbon network with ultrathin nanosheets of 50 nm. It has high specific surface area of 3028 m2 g−1, good e-conductivity of 43 S m−1, ultrahigh C/O ratio of 27.4 and high sp2 carbon content of 90%. Thus, the voltage window upper limits can be raised up to 3 V in TEABF4/PC and 3.5 V in EMIMBF4 electrolytes. In TEABF4/PC electrolyte, this HPC displays high Cg of 124 F g−1 at 0.05 A g−1 with C10/0.05 as high as 70.8% and ultralong lifespan of 94% after 20,000 cycles. In EMIMBF4 electrolyte, the energy density can reach up to 56.6 Wh kg−1.