Vanadyum Redoks Akış Bataryaları İçin Kullanılabilecek Elektrolitlerin Karbon Bazlı Elektrot Yüzeyindeki Elektrokimyasal Davranışlarının İncelenmesi
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In this thesis, the electrochemical behavior of acidic electrolytes and their usability that can be used for vanadium redox flow batteries (VRAB), were investigated. In these analyzes, the electrochemical behavior of vanadium electrolyte solutions containing sulfuric acid (H2SO4), phosphoric acid (H3PO4), methanesulfonic acid (CH3SO3H), oxalic acid (H2C2O4), hydrochloric acid (HCl), perchloric acid (HClO4) and acetic acid (CH3COOH) were investigated by cyclic voltammetry and electrochemical ımpedance spectroscopy methods. In the selection of these acids, industrial usage prevalence, relative costs and suitability for vanadium redox flow batteries were taken into consideration. All types of vanadium ions (VO2+, VO2+, V3+, V2+) used in formed in the vanadium redox flow battery change form and form precipitate in more basic solutions having pH> 4 properties. Therefore, the vanadium solution should be sufficiently acidic. In this study, the cyclic voltammetry method used in the study of the electrochemical behavior of acidic solutions determined the working ranges and reduction-oxidation voltages for each solution and blank solutions with a concentration of 0.5 M VOSO4. Using the cyclic voltamograms taken in the anodic and cathodic region, the working limits of these solutions in the graphite disc electrode were determined. Reduction-oxidation behaviors in these potentials were examined. On the graphite or graphite composite electrodes of acidic electrolytes, that are used for the operation of vanadium redox flow batteries with high efficiency, high energy density and having long charge-discharge cycle numbers. It is necessary to control the formation of unwanted hydrogen gas evolution in the catholyte compartment and corrosion and degradation reactions of graphite in the anolyte compartment. For this reason, shifting the GIC formation to more positive potentials on the graphite electrode surface in the studied electrolyte, thus preventing the GIC formation at lower potentials and preventing the graphite or graphite composite electrodes In addition, in order to operate these redox flow batteries with high efficiency, hydrogen formation must be suppressed in the cathode and catholyte compartment. In this context, it is desired that the hydrogen formation appearance potential is as high as possible (hydrogen overvoltage is large and current density is low). For all these reasons, the behavior of the acidic solutions used in the study in the anodic and cathodic region was examined by taking these criteria into consideration. In the other stage of the study, the impedance measurements of different solutions and different potentials at these solutions were made by graphite disc electrode and the equivalent circuit model Rs(C(RctQ)) was determined according to these parameters. The Rs value change here depends on ionic conductivity, but does not vary greatly in acids that decompose to a large extent. The low Rct resistance, which expresses the charge transfer resistance, means the electron transfer rate is high. In addition, at this stage of the study, the results of the impedance analysis obtained by performing EIS measurements at different VOSO4 concentrations in eight different acids were compared and evaluated.