▎ 摘　　要

In general, reduced graphene oxide (RGO) is prepared by conventional chemical methods using various reducing agents. The quality and properties of RGO depend on extend of exfoliation and the nature of the reducing agent used for the reduction of graphene oxide (GO). In this work, GO is prepared by modified Hummers' method and subsequent ultrasonic exfoliation. Then it is hydrothermally reduced to RGO using different amounts (0, 5, 10, 20 and 30 mL) of ethanolic extract of the environmentally threatening invasive weed, Prosopis juliflora. The ethanolic extract of the weed plays multiple roles: (i) reducing GO, (ii) doping nitrogen and (iii) incorporating spacer. The textural properties and surface functionalities (oxygen and nitrogen-based) and thus the capacitance properties of RGO largely depend on the amount of ethanolic extract of the weed used to reduce GO. RGO obtained by reducing GO using a different amount of ethanolic extract of the weed is referred to as RGOXE, where X refers to the amount of ethanolic extract of the weed. The value of specific capacitance follows the order: RGO10E (170 F g(-1)) > RGO5E (160 F g 1) > RGO20E (112 F g(-1)) > RGO30E (98 F g(-1)) > pristine GO (88 F g(-1)). Besides the high value of specific capacitance, RGO10E demonstrates good rate capability (retains 67% of its initial specific capacitance value on increasing the current density from 0.5 to 10 A g(-1)) and stable cycle-life (retention of 100% specific capacitance for the tested number of 10,000 cycles). In addition, symmetric supercapacitor fabricated using RGO10E delivers energy density of 4.9 Wh kg(-1) at a power density of 496 W kg(-1).