Preparation and Characterization of Heteroatom Self-doped Activated Biocarbons as Hydrogen Storage and Supercapacitor Electrode Materials

Abstract 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 m2 g−1 and nitrogen content of 1.67 wt%. The specific surface area (SBET) and micropore volume (VDR) 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.