Honeycomb-like hierarchical porous carbon derived from kapok fiber for supercapacitors

The fine structural engineering of biomass -derived porous carbon is the key to maximize the specific capacitance and rate performance of capacitive carbon. Herein, a hierarchical porous carbon (HPC) has been fabricated from kapok fiber via oxalic acid hydrothermal coupled chemical activation strategy. Moderate concentration of oxalic acid hydrothermal treatment is beneficial to increase the concentration of concentration of C-O, C--O, and sp2 hybrid carbon atoms on fiber surface, and chemical activation accelerate the growth of integrated honeycomb microstructures and hierarchical pores, especially 1.0-2.0 nm micropores. The optimized HPC shows a high specific surface area of 2045 m2 g-1, moderate meso-macropore volume of 0.13 cm3 g-1, low ID/IG of 0.95, and well -developed honeycomb structure, which endows HPC with high ions adsorption capacity and fast kinetic behavior. The optimized HPC exhibits a high specific capacitance of 305.5 F g-1 at 0.5 A g-1 and 194.0 F g-1 at 50 A g-1 in 6 M KOH electrolyte, with a high capacitance retention of 63.5 %. The assembled supercapacitor based on HPC delivers a higher energy density of 10.2 Wh kg- 1 at power density of 150 W kg- 1 in KOH electrolyte and 27.7 Wh kg- 1 at 225 W kg- 1 in Na2SO4/PVA gel electrolyte, and superb capacitance retention of 95 % for 20,000 cycles. This will also provide a potential strategy for biomass micro -composition modulation and hierarchical porous carbon structural regulation toward high performance electrode materials.