Graphene has attracted tremendous attention in spacious energy storage fields due to its high conductivity, excellent electrical and mechanical stability, and large specific surface area [1]. However, graphene shows lower electrochemical performance than theoretical reports because of restacking or agglomeration induced by strong van der Waals interactions between adjacent layers. To prevent this phenomenon and improve electric properties, transition metal oxides or hydroxides are generally introduced into the interlayer of graphene [2]. Among diverse transition metal oxides, TiO₂ which has numerous advantages such as a high specific energy density, strong oxidizing power, low cost and environment friendly considered as a promising electrode material. In reported study, TiO₂ / rGO composite was synthesized by two-step method [2]. Herein, we firstly designed a facile one-step method through the sol-gel approach to synthesize TiO₂ / rGO composites, and they exhibited excellent electrochemical performances.

   Graphite oxide (GO) was synthesized by a modified Hummers method [3] and as reported before [4-5]. GO was dispersed in DI water and sonicated for 30 min. The mixture of titanium (IV) isopropoxide (TIP), ethanol and acetic acid added in the GO solution. Ammonium hydroxide was then added until pH 8~9 in dropwise under stirring for 1 hour at room temperature to form a brownish-black suspension. After this process, the obtained solution was sealed into a Teflon lined stainless steel autoclave at 160ºC for 3 hours. We can finally obtained TiO₂ / rGO composite after filtering, washing and drying in air at 60ºC for 12 hours.

   We analyzed morphological properties of the synthesized composites using scanning electron microscopy (SEM), transition electron microscopy (TEM), X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR). We confirmed TiO₂ / rGO hybrid composites were well anchored on the interlayer of the graphene nanosheets. We also examined electrochemical performances of the composites with cyclic voltammetry (CV), electrical impedance spectroscopy (EIS) and galvanostatic charge-discharge curve. We studied a facile one-step sol-gel method for synthesis of titanium dioxide (TiO₂) / reduced graphene oxide (rGO) composite. In conclusion, the as-prepared composite can be considered as promising electrode materials owing to high capacitance and long cycle life.

Acknowledgments

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning, Korea (Grant No.: NRF-2011-0009007).

References