Plant extract assisted synthesis of cobalt doped nickel oxide nano structures for high-efficient supercapacitor electrodes

• The Co doping on NiO NSs was successfully made without crystal structure distraction. • M. ferruginea leaf extract was used to synthesize the NSs for the first time. • A new electrode composition of rGO, PVA, and the active material was fabricated. • The capacitance of NiO NSs was enhanced by Co doping to more than 2.9 times. The development of green energy source parallel to the advancement of high capacity storage device has been taken as the main out way from the energy related crisis. The nickel based supercapacitors exhibiting smart electrochemical properties attract most researchers’ attention. In this study, NiO nanostructures (NSs) doped with cobalt (Co) at Co:Ni ratios of 0.0, 0.01, 0.03, 0.05, and 0.07 were synthesized by Millettia ferruginea ( M. ferruginea ) leaf extract assisted co-precipitation method for supercapacitor electrode fabrication. The X-ray diffraction (XRD) pattern confirmed the formation of face-centered cubic (FCC) NiO crystal and Co ion substitution for Ni, with crystallite size decreased as Co doping increased. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images revealed semi-spherical particles. The high resolution (HR-TEM) image confirmed crystallinity, showing an inter-planar distance of 0.0242 nm, closely matched the XRD results. The electrochemical study displayed an improvement in specific capacitance of Co doped NiO NSs compared to the undoped NiO NSs. The higher specific capacitance (1,107.3 Fg -1 ) was obtained at 0.5 Ag -1 and capacitance retention of 83.16% at 4 Ag -1 from the C 1 @Ni NSs with a smaller particle size. This suggests that Co doped NiO NSs could be a promising electrode material for energy storage. The Co doped NiO NSs was synthesized from Co and Ni salts using the M.ferruginea leaf extract. The synthesized NSs was used to fabricate an electrode in combination with rGO and PVA, and then pasted on Ni foam. The dried electrode was characterized using three electrode electrochemical cell.