GRAPHENE NANORIBBONS AND THEIR POLYMERIC NANOCOMPOSITES: CONTROLLED SYNTHESIS, CHARACTERIZATION AND APPLICATIONS

Carbon based materials are very promising as electrode materials energy generation and storage devices. They have been used for fuel cells, supercapacitors and solar cells. Among the carbon-based materials, graphene is very attractive due to its unique properties such as high electrical conductivity, good mechanical flexibility, large theoretical surface area (2630 m2/g), and high thermal and chemical stability. These unique properties make them very suitable for energy storage applications particularly for supercapacitors. The performance of the graphene as energy storage material could be further improved by growing them in nanoribbon form by unzipping carbon nanotubes. In this thesis, we report synthesis and characterization of graphene nanoribbons from multiwall carbon nanotubes (MWCNT). The synthesized graphene nanoribbons were structurally and electrochemically characterized. The shift of (002) peak in graphene nanoribbons compare to MWCNT confirms unzipping of MWCNT and its exfoliation. Other materials such as conducting polymers have been also used for energy applications. The performance of the conducting polymers such as polyaniline can be improved by making composites with graphene. We have found that nanocomposites of polyaniline with graphene nanoribbons (PA-GNR) have better performance for energy storage applications. The performance of the nanocomposites, polyaniline and graphene nanoribbons were electrochemically tested using cyclic voltammetry and galvanostatic charge-discharge methods. Cyclic voltammetry was performed at various scan rates to understand the charge transport mechanism. It was observed that the specific capacitance of the PA- GNR nanocomposites decreases with increasing scan rate. The overall charge storage capacity of the PA-GNR composites was higher than that of GNR. The higher charge storage capacity of the PA-GNR composites is due its enhance surface area and synergistic effect between polyaniline and graphene nanoribbons. A symmetric supercapacitor device was fabricated using PA-GNR composite. The effect of temperature on the charge storage capacity of the device was tested. It was observed that the charge storage capacity of the supercapacitor device increases with increase in temperature. The results suggest that graphene nanoribbons and composites of polyaniline with graphene nanoribbons could be used as an electrode material for supercapacitor applications