Hierarchical porous biomass carbon derived from cypress coats for high energy supercapacitors

In the present work, we report a simple two-step process to fabricate hierarchical porous carbon from biomass. The so-called two-step refers to hydrothermal carbonization of cypress coats followed by activation with KOH. The morphology and porous parameters of the resulting porous carbon can be controlled by adjusting KOH/carbon mass ratio during activating stage. The optimal sample (SHPC-2) has a hierarchically porous structure containing micropores and meso-/macropores, high specific surface areas (1325.9 m2 g− 1) with appropriate pore size and hydrophilous surface properties due to rich nitrogen and oxygen co-doping. The electrochemical measurements show the as-prepared SHPC-2 exhibits a high specific capacitance (345 and 330 F g− 1 at 1.0 A g− 1) and better rate capability (75.4% and 87.8% capacitance retention at 50 A g− 1) in 1 M H2SO4 and 6 M KOH, respectively. Furthermore, the assembled symmetric supercapacitor based on SHPC-2 and filled with 1 M Na2SO4 electrolyte delivers an outstanding energy storage performance (energy density of 30.5 W h kg− 1 at power density 900 W kg− 1) with good cycling stability (86.2% retention after 10000 cycles at 5 A g− 1). These results indicate that the eco-friendly carbon materials derived from biomass have a huge potential in the applications of high-performance electrode materials for supercapacitors.