Flexible fiber hybrid supercapacitor with NiCo₂O₄nanograss@carbon fiber and bio-waste derived high surface area porous carbon

Flexible, light weight and portable energy storage devices are receiving much attention for flexible electronic applications. Nonetheless, these conventional two-dimensional (2D) or planar structured flexible energy storage devices could not meet the demand for wearable or textile electronics. To meet this demand, in this work, a novel flexible fiber hybrid supercapacitor (HSC) is fabricated using NiCo2O4nanograss (NG)-array coated carbon fiber (NiCo2O4NG@CF) as the positive electrode to provide a pseudocapacitance and porous carbon coated carbon fiber electrode as the negative electrode to provide an electric double-layer capacitance (EDLC). Particularly, the porous carbon is prepared from Lemon peel waste to obtain a low cost electrode material. Interestingly, the fabricated HSC exhibits a maximum specific capacitance of 17.5 F g-1(25.03 mF cm-2) and an energy density of 6.61 Wh kg-1(9.46 μWh cm-2) at the current of 1 mA, which is far better than previous reports. Moreover, three knitted fiber HSCs connected in series could successfully power up a red LED, even at a folded condition. It is believed that this type of fiber HSC could be a potential candidate for flexible/wearable electronic applications.