Fabrication of flexible reduced graphene oxide-TiO2 freestanding films for supercapacitor application

This paper described the fabrication of a flexible composite film electrode (rGT) composed of reduced graphene oxide (rGO) and TiO2 in an aligned stacking structure of rGO/TiO2 layers using a simple vacuum-assisted filtration method. The SEM images of rGO and rGT films indicate that the rGO film (d = 5.6 +/- 0.5 mm) was highly expanded into a layered structure of rGT (d = 7.2 +/- 0.5 mm) intercalated by the TiO2 nanoparticles, which prevent the interlayer stacking of graphene sheets. The intensities of C-O and C=O bonding peaks in X-ray photoelectron spectra of rGT films decreased dramatically, as the reduction temperature was increased from 100 to 600 degrees C, indicating almost complete removal of the oxygenated functional groups. Hence, the electrochemical properties of rGT film electrodes significantly relied on the reduction temperature of graphene oxide (GO)-TiO2 film. The rGT(600) electrode (annealed at 600 degrees C) in 1.0 M Na2SO4 aqueous electrolyte exhibited the specific capacitance of 286 F g(-1) in addition to the excellent cycling stability with 93% capacitance retention after 1000 continuous charge/discharge cycles at 1 A g(-1). The specific capacitance of the rGT600 electrode in the expanded interlayer stacking structure of rGO and TiO2 particles was by 63% higher than that of the three-dimensional TiO2-graphene hydrogel electrode (175 F g(-1), 1 A g(-1)) prepared using a one-step hydrothermal approach. The modification in the preparation of the composite films comprising rGO sheets and TiO2 particles optimized the supercapacitor electrodes into the expanded interlayer stacking rGO/TiO2 structure, exhibiting excellent electrochemical performance, which is required for the development of advanced micro-size and flexible electrodes in energy storage devices.