Superior supercapacitance behavior of oxygen self-doped carbon nanospheres: a conversion of Allium cepa peel to energy storage system

Mesoporous carbon nanospheres are produced from biowaste, Allium cepa peels, well known as onion dry peels using the catalyst-free pyrolysis method. The synthesis process involves an unusable bio-precursor that is accumulated in millions of tons per year. The obtained materials show nanosphere morphology with particles size of 63-66 nm and surface area up to 2962 m(2) g(-1). After pyrolysis at 800, 900, and 1000 degrees C, the carbon nanospheres are directly applied for supercapacitance study without further activation processes. The electrochemical studies show promising results such as high electrode capacitance of 189.4 at 0.1 A g(-1) in 3 M KOH. Moreover, full cell symmetrical supercapacitor is fabricated and further investigated under a wide potential window up to 1.6 V. An excellent electrochemical behavior is observed for the supercapacitor in terms of high energy density of 22.1 Wh kg(-1) at a power density of 39.6 W kg(-1), high cyclic stability of 78%, and high coulombic efficiency of 90% over 4500 cycles at 0.5 A g(-1). These studies support carbon nanospheres obtained from Allium cepa wastes to be used as promising materials for supercapacitor application.

Automated summary

Mesoporous carbon nanospheres are successfully synthesized from Allium cepa peels using a catalyst-free pyrolysis method, demonstrating high surface area and small particle size. These nanospheres exhibit promising electrochemical performance for supercapacitor application, including high energy density, cyclic stability, and coulombic efficiency.