Green synthesis of nitrogen self-doped porous carbons from waste garlic peels for high-performance supercapacitor applications

Based on the biological structure of biomass materials, the preparation of carbon materials with special pore structures and rich surface groups is an important route in the development of new carbon materials for electrodes. In this work, a nitrogen self-doped carbon with unique tubular channel structures was synthesized from garlic peels for the high-performance supercapacitor electrode application. The mild KHCO3 was selected as the activator and therefore the biological structure of garlic peels is well preserved, showing a large number of long tubular channels with a diameter of around 50 nm. It was found that a nitrogen self-doped porous carbon material (SPC-4KC) with a nitrogen relative content of 1.77% and a large specific surface area of 1993.73 m2 g−1 was formed at 800 ℃ at a KHCO3/SPC mass ratio of 4:1. Using as the electrode material, the mass-specific capacitance of the SPC-4KC-based electrode reached 303.38 F g−1 at a current density of 1 A g−1 in the three-electrode system. In the two-electrode system, when the energy density is 7.42 W h kg−1, the power density is 314.33 W kg−1. Also, the material exhibits excellent cycle stability, with a capacitance retention of 94.87% after 5000 cycles at a current density of 10 A g−1.