A novel approach for preparing in-situ nitrogen doped carbon via pyrolysis of bean pulp for supercapacitors

The preparation of activated carbon by complex and expensive nitrogen doping and activation process has been studied extensively. N-doped activated biochar or carbon material prepared from renewable and low-cost biomass has arisen more and more attention due to the hierarchical porous structure and abundant nitrogenous functional groups in the application of supercapacitors. Herein, a method for preparation of in-situ nitrogen doped activated carbon derived from bean pulp (BPC) by one-step carbonization and CO2 activation at 1073 K was proposed. The morphological structure, specific surface area (SSA), pore size and nitrogen-containing functional group compounds could be controlled by the adjustment of CO2 concentration. The maximum SSA could be up to 558.2 m2 g−1 for BPC. The N content increased from 5.0% to 10.0% with the increase of CO2 concentration from 0 to 50 vol%. In addition, pyridine, pyrrole, graphite, and nitrous oxide were detected and analyzed, in which pyridine and pyrrole nitrogen enhance the pseudocapacitance. A maximum specific capacitance of BPC-50 reached 106 F g−1 at 0.25 A g−1. The capacitance retention maintained 93% at 10 A g−1 after 20,000 cycles in the symmetrical supercapacitor with a 6 M KOH electrolyte. Schematic diagram representing synthesis of BPCs. [Display omitted] •In-situ N doped porous activated carbon was prepared from bean pulp.•Morphology structure and chemical composition were controlled by CO2 concentration.•Maximum specific surface area of 558.2 m2 g−1 for BPC-100.•The capacitance of BPC-50 reached 106 F g−1 and maintained 93% after 20,000 cycles.