From onion skin waste to multi-heteroatom self-doped highly wrinkled porous carbon nanosheets for high-performance supercapacitor device

Herein, we report the synthesis of N, S, P-self-doped porous and wrinkled graphene-like carbon nanosheets derived from the abundant waste onion skin via carbonization and activation strategy. The optimized onion skin derived carbon (OnC-900) exhibits highly wrinkled graphene-like morphology and multi-heteroatom doping without any external dopants is confirmed via field emission scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. The OnC-900, acting as a supercapacitor electrode, exhibits excellent specific capacitance of 478 F g(-1) at a current density of 1 A g(-1) and maintains 241.7 F g(-1) even at 6.7 A g(-1) in the three-electrode cell indicating its excellent rate capability. The assembled symmetric supercapacitor device using aqueous neutral electrolyte (1 M Na2SO4) delivers outstanding specific energy of 17 Wh kg(-1) with a wide potential window up to 1.4 V. The device also exhibits excellent cyclic stability by retaining 93% of initial capacitance over 10,000 cycles at a current density of 3 A g(-1). This enhanced performance of the electrode is mainly due to the high specific surface area and the heteroatom co-doping that provides improved surface wettability by polarized surface, induced pseudocapacitance effect, and improved electronic conductivity. These results demonstrate that onion waste derived multi-heteroatom co-doped graphene-like carbon nanosheets have great potential for renewable and sustainable energy storage devices.