Preparation and characterization of heteroatom self-doped activated biocarbons as hydrogen storage and supercapacitor electrode materials

This manuscript describes cost-effective synthesis of heteroatom self-doped activated biocarbons from sword bean shells (ACBS) by a simple two-step process of carbonization and activation using different weight ratios of KOH/chars. The results showing as-prepared samples at different weight ratios present prevailing characteristics with mainly micropores , surface area as high as 2838 m 2  g −1 and nitrogen content of 1.67 wt%. The specific surface area (S BET ) and micropore volume (V DR ) of the ACBS samples significantly contribute to hydrogen uptake, and at 77 K, these values can reach up to 2.63 and 5.74 wt% at 1 bar and 40 bar, respectively. In addition, the ACBSs exhibit a high specific capacity of 183 F g −1 at 2 mV s −1 and 211 F g −1 at 0.5 A g −1 from CV and GCD analysis in a three-electrode system. The button cell CR 2032 devices assembled by two solid-state symmetric electrodes from ACBSs also present a high energy density of 19.5 W h kg −1 at 10 A g −1 . These devices also demonstrate superior cycling stability and rate performance with capacitance retention of nearly 100% capacity after 5000 cycles at a current density of 1 A g −1 . These results suggest that the as-prepared nitrogen-doped porous carbon material has a promising potential for energy conversion and storage devices or for hydrogen adsorptions.