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

Abstract

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 μm) was highly expanded into a layered structure of rGT (d = 7.2 ± 0.5 μm) intercalated by the TiO₂ nanoparticles, which prevent the interlayer stacking of graphene sheets. The intensities of C–O and CO bonding peaks in X-ray photoelectron spectra of rGT films decreased dramatically, as the reduction temperature was increased from 100 to 600 °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 rGT₆₀₀ electrode (annealed at 600 °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.