Süperkapasitör Enerji Depolama Uygulamaları İçin Nano-Boyutlu Metal Oksit İçeren Polipirol Esaslı Kompozit Malzemelerin Elektrokimyasal Sentezi
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There is an increasing demand for the development of high performance, clean and sustainable energy systems and energy storage due to the rapid depletion of fossil fuels, and their environmental issues. One of the important candidates among energy storage system is the supercapacitors due to their high power density, efficiency and cycle life. This dissertation aims to investigate the galvanostatic synthesis of polypyrrole (PPy) composites with nano-structured VOx, PbOx, Ag-Ag2O, MnOx, CoOx, NiOx, and FeOx on their own metal (M)-intercalated graphite surfaces. PPy and metal oxides were simultaneously synthesized by using galvanostatic method in acetonitrile solution containing pyrrole, MBF4 salts, tetrabutylammonium tetrafluoroborate (TBABF4), HBF4, H2O, and sodium carboxymethyl cellulose (CMC). The effects of additives and graphite intercalation on the capacitive behaviors of PPy/MOx/CMC composites (4.0 mg/cm2, 0.0244 cm2) were studied in 100 mM H2SO4 solution by using cyclic voltammetry and electrochemical impedance spectroscopy (EIS) methods. XRD, TEM, XPS, SEM-EDX, and BET techniques were used for the composite characterization. It was determined that nano-sized (3-100 nm) metal oxides homogeneously dispersed in PPy, and the coating surface areas increased, compared to homopolymer. The capacitive properties of the composite coatings were examined by means of the galvanostatic charge-discharge test. The highest specific capacitance value was recorded for PPy/PbOx/CMC coating, whereas the lowest was for PPy/FeOx/CMC coating. For applications, the capacitive behaviors of composites (10.0 mg cm-2, 0.2 cm2) were examined in split test cell with two electrodes (symmetric and asymmetric) containing polyvinyl alcohol-H2SO4 gel electrolyte. PPy composites with PbOx, VOx and MnOx were also tested with higher electrode area (1.0 cm2 and 6.25 cm2). The highest specific capacitance (165 F g-1), energy density (22.9 Wh kg-1), and power density (0.36 kW kg-1) at 2.0 A g-1 were determined for asymmetric supercapacitor based on PPy/PbOx/CMC composite (10.0 mg cm-2, 1.0 cm2) on Pb-intercalated graphite sheet. The asymmetric cell in a potential range of 1.0 V maintained 91% of its capacity after 1000 cycles. Lastly, a three asymmetric cell stack with the nano-sized PbOx dispersed PPy composite electrode yielded 3.0 V potential. The findings in the study, demonstrate the viability of asymmetric supercapacitor, are promising for the possible future applications.