Pre-Carbonization of B/N/O heteroatom-codoped hierarchical porous carbon spheres derived from bio-waste orange peel for high-performance supercapacitors

Here, boron, nitrogen, and oxygen heteroatoms-doped hierarchical porous carbon spheres (HPCS) have been produced by consuming scrap bio-waste orange peel as a natural carbon precursor in a low-cost production technique. The synthetic method provides a quick and environmentally friendly approach for fabricating B/N/OHPCS by annealing carbon materials with boric acid followed by NaOH activation. Additionally, autoclave pre-carbonization promotes the polymerization of the precursors, leading to an increased carbon yield. The synthesis of B/N/OHPCS products with a multi-scale pore structure can enhance specific capacitance activity because of the synergistic usage of heteroatoms, efficient mass transfer, and improved transport kinetics from linked 3D architecture. As a result, the B/N/OHPCS-750 pre-carbonization material for the Supercapacitors (SC) exhibits a high specific capacitance of 436 F g^-1 at 0.5 A g^-1 in 1 M Na₂SO₄. Also, the B/N/OHPCS-750-based symmetric SC demonstrates exceptionally high specific capacitance of 365 F g⁻1 at a current density of 0.5 Ag⁻1 and an impressive power density of 456.2 W kg⁻1 and an energy density of 28.6 Wh kg⁻1. Notably, the SC maintains outstanding capacitance retention of about 92 % even after 30,000 charge-discharge cycles at a high current density of 10 Ag⁻¹. This study displays the excellent performance of SCs fabricated with heteroatom-doped HPCS, synthesized via a salt-assisted method, offering an eco-friendly solution for converting bio-waste into valuable materials.