Investigation of the supercapacitor and sensor performanceof nanoporous carbon fiber and graphite

Carbon based materials possess a wealth of functionalities, such as good electrical and thermal conductivities, high resistance to chemicals and high thermal stability. All of these merits make it an indispensable component for many high-tech applications such as electrical devices and energy storage. Beyond their outstanding electrical and thermal properties, carbon fibers can be used as composite preparation in many applications such as airplanes, vehicles, and cables with their high tensile and compressive strength. Due to its superior electrical and mechanical properties, serial production of graphene has become a very important field of study. Many graphene preparation methods have been developed since its discovery. Electrochemical methods have been employed to produce graphene as an industrial scale production technique. Here we report a prompt preparation of graphene-coated carbon fibers into an aqueous solution with a simple continuous electrochemical method. Therefore, these graphene structures led to the formation of a nanoporous surface on the carbon fiber. In the currently designed electrochemical exfoliation route, mass production of graphene-coated carbon fiber was produced within short reaction time, around 5 minutes for 1-meter tow fiber. The structural, thermal and surface characteristics of graphene-coated carbon fibers were investigated by Raman spectroscopy, Fourier transforms infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA) and scanning electron microscope (SEM) instrumentations. Electrochemical properties of graphene-coated carbon fibers as supercapacitor electrodes were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Cyclic charge-discharge test display a higher specific capacitance, 3 times higher than that of the pure carbon fiber based supercapacitor. Moreover, mechanical performance of graphene coated carbon fiber, graphene oxide-coated carbon fiber, and bare carbon fiber was investigated. The results of the mechanical properties tests show that the surface treatments did not adversely affect the mechanical properties of nanoporous carbon fiber. Our present method shows huge potential for industrial-scale production of high-quality graphene oxide coated carbon fiber and graphene-coated carbon fibers further commercialization of both graphene-coated fiber and graphene oxide coated carbon fiber for numerous advanced applications in energy storage devices and composite. Graphite electrodes were coated by nanoporous carbon based structures by cyclic voltammetry and electrochemical sensor properties were investigated. In this study, a simple and rapid analysis method was proposed to determine Pb2+ and Cd2+ in water samples with nanoporpus graphite electrode. Nanoporpus graphite electrodes were prepared by the potential cycling between -0.3 V and 2.0 V in 0.1 mol/L H3PO4 solution to improve electrochemical sensing capability for Pb2+ and Cd2+ ions. The electroanalytical parameters affecting the determination of Pb2+ and Cd2+ have been optimized according to experimental studies. Magnitude of the oxidation peak currents were used to get the optimal value of each parameter. Use of optimized method with the resulting nanoporous electrode showed good selectivity and sensitivity on the determination of Pb2+ and Cd2+ ions. The resulting sensor has been successfully tested on standard reference water sample. Under optimized conditions, the limits of detection were 0.46 µg/L for Pb2+ and 1.11 µg/L for Cd2+. Linear working ranges for Pb2+ and Cd2+ ions were found to be 5-45 µg/L and 10-40 µg/L, respectively. After these studies, nanoporous graphite electrodes were prepared which were used for electroanalytical determination of Mn2+ and Cu2+ ions (Mn2+ ions determined by cathodic stripping voltammetry, while Cu2+ ions were determined by anodic stripping voltammetry). Therefore, graphene oxide coated graphite electrodes were used. Graphene oxide coating parameters and electroanalytical method parameters are optimized respectively. The developed nanoporous, functional electrochemical sensors and electroanalytical methods have been successfully tested in the certified reference water sample. Linear working ranges were 4-28 ppb for Mn2+, and 5-25 ppb for Cu2+. Limits of detection values were determined as 0.41 ppb for Mn2+ and 1.23 ppb for Cu2+.