Development and characterization of carbon nanofiber supercapacitor electrodes modified by graphene conductive polymers (PEDOT:PSS, PANI)

In order to use renewable energy effectively, it is important to use it together with energy storage technologies. Supercapacitors are energy storage technologies that fill the gap between Li-ion battery technology and conventional capacitors in terms of power and energy density. Within the scope of this thesis, it is aimed to increase the electrochemical performance by modifying the carbon nanofiber electrode material with various materials (graphene, PEDOT: PSS, and PANI) and methods (electrospinning, electrospray, dip coating, and nanofiber yarn production). For this purpose, PAN nanofiber production parameters were optimized to produce smooth, homogeneous, continuous, fast and fine nanofiber, and then nanofibers with an average diameter of 233±32 nm were produced under optimized conditions. After stabilization and carbonization process, nanofiber diameters were measured as 209±16 nm and 140±17 nm, respectively. In the next study, PAN/PVA hybrid nanofiber structures were produced in different mixing ratios and porous carbon nanofiber electrodes were obtained by removing PVA from the nanofiber structure during production. The chemical, morphological, and electrochemical performance of porous carbon nanofiber electrodes with the increased surface area were investigated. It was determined that the specific capacitance value of the EK5 electrode produced from hybrid nanofiber containing 33% PVA at 5 mV/s scan rate was improved by 64% compared to the neat carbon nanofiber and the specific capacitance value was measured as 268 F/g. In addition, porous carbon nanofiber electrodes retained approximately 100% of the specific capacitance during 2500 test cycles and exhibited superior cyclic stability. In the next study, PEDOT:PSS, a water-soluble conductive polymer, was coated on the carbon nanofiber surface in different thicknesses using the dip-coating method, which is an easy, fast and scalable method, and the effect of the PEDOT:PSS coating process on the electrochemical performance of the carbon nanofiber was investigated. The neat carbon nanofiber diameter of 155.44 nm was measured as 194.45 nm after 9 layers of PEDOT: PSS coating. After 9 layers of PEDOT: PSS coating (9P-KNF), the highest specific capacitance was obtained as 175 F/g at 10 mV/s scan rate, this value was approximately 75.9% higher than the specific capacitance value of the neat carbon nanofiber. After 2500 cycles, it showed an 80% capacitance retention. In another study, by adding graphene oxide (GO) in different mixing ratios such as 1, 2, 5, 10, and 20% into the PAN solution before electrospinning, graphene oxide-reinforced PAN nanofibers were produced. The produced nanofiber mats were stabilized and carbonized so that different proportions of graphene-reinforced carbon nanofiber structures were obtained. Afterward, hierarchical synthesized the conductive polymer of polyaniline (PANI) was integrated into the 10% GO-reinforced carbon nanofiber electrode, which showed the best electrochemical performance (the specific capacitance value of the KPGO10 electrode was calculated as 164 F/g at a scan rate of 5 mV/s), by the vacuum-assisted filtration method. The performance of the graphene-reinforced carbon nanofiber electrode modified with PANI was examined and it was seen that the specific capacitance value was improved by about 20%. In the next study, the graphene oxide dispersion was electrospray coated on the PAN nanofiber surface in different proportions such as 4, 8, 20%. GO-coated PAN nanofiber surfaces have been stabilized and carbonized to obtain graphene-coated carbon nanofiber surfaces. The electrochemical performances of the obtained supercapacitor electrodes were examined and it was seen that the best results were obtained with 8% GO-electrosprayed carbon nanofiber electrodes. In the last study, PAN nanofiber yarns were obtained from the PAN nanofiber yarn structure obtained by electrospinning and then the twisting process. The obtained PAN nanofiber yarns were stabilized and carbonized and carbon nanofiber yarns were obtained. Then morphological and electrochemical performances of carbon nanofiber yarns were examined. The specific capacitance value of the CNF yarn electrode was measured as 145 F/g at a current density of 0.2 A/g, and it was found that the specific capacitance value increased by approximately 20% up to 500 cycles, then remained approximately constant until 1000 cycles.