High electrochemical performance flexible solid-state supercapacitor based on Co-doped reduced graphene oxide and silk fibroin composites.

A simple method for the preparation of flexible supercapacitor based on Co-doped reduced graphene oxide (rGO) and silk fibroin composites film is reported. The facile and cost-effective green pathways are chosen to reduce the exfoliated graphite oxide using a microbial strain, at room temperature. Doping process is performed by using in-situ precipitation technique. The Co-doped reduced graphene oxide (Co-rGO) is characterized by X-ray diffraction, Raman spectroscopy and Scanning Electron Microscopy (SEM). The as-prepared Co-rGO and silk fibroin are used to prepare flexible electrode for supercapacitor device. Electrochemical performance of the electrode is examined using cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. The fabricated supercapacitor shows the specific capacitance of 104 F g−1 at a current density of 0.5 A g−1 in ionic liquid electrolyte (EMIm+BF4−). After a charge–discharge rate of 1 A g−1 for 10,000 cycles, the Co-rGO film exhibits remarkable electrochemical stability with the capacitance retention ratio of 89%. Furthermore, the Co-rGO film based supercapacitor achieves high energy density up to 28.31 Wh kg−1 at a power density of 78.24 kW kg−1 by using the ionic liquid electrolyte. The results shown in this work indicate that our proposed Co-rGO-silk fibroin composites film is a promising electrode material for manufacturing flexible supercapacitors.