High-performance flexible wire-shaped electrochemical capacitors based on gold wire@reduced graphene oxide

Flexible gold @reduced graphene oxide sheathed wires (WAu@rGO) were prepared by soaking a gold wire (100μm in diameter) in the center of glass capillaries with inner diameters of 1.0, 1.3 and 1.8 mm in a suspension of graphene oxide (GO) in a L-ascorbic acid aqueous solution at 30 °C for 48 h. The WAu@rGO wires were obtained after removal of the capillaries, and their microstructures were characterized by SEM and their electrochemical properties as flexible electrodes in electrochemical capacitors were investigated by electrochemical tests. Results show that the specific capacitance of the WAu@rGO wire with the smallest diameter is 5.47 mF cm−1 or 176.7 F g−1 at a scan rate of 1 mV s−1. A symmetric all-solid-state flexible electrochemical capacitor based on the two smallest wires and a polyvinyl alcohol/H3PO4 gel electrolyte shows a maximum capacitance of 2.06 mF cm−1, or 6.87 mF cm−2 or 411.9 mF cm−3. The solid-state capacitor has energy and power densities of 9.48×10−4 mWh cm−2 and 0.017 mW cm−2, respectively, based on the whole device. Three devices connected in series can light a light-emitting diode with a threshold voltage of 2.5 V. Moreover, the device also shows a long cyclic stability and a good bending ability.