Elektrik Enerjisi Depolama Sistemi Olarak Tüm Krom ve Demir-Krom Redoks Akış Bataryaları İçin Elektrolit ve Elektrot Geliştirilmesi

Abstract

Due to their unique features of having a modular design for power and energy requirements of myriad applications, Redox Flow Batteries (RFB) are very promising among other energy storage systems. RFB Technology, provides alternative solutions especially for the sustainability of renewable energy sources such as solar and wind, and balance and supply of power consumption. Despite its advantages and cost effectiveness compared to other energy storage technologies in large-scale energy storage applications, their low energy and power density values and the cost of system components, especially electrolytes, which constitute the system, stand out as a serious problem in the commercialization of RFB technology. The aim of this dissertation, is to compare RFB systems containing all chromium and iron-chromium which are abundant in Turkey for reserve, to commercially equivalent technologies and to specify and improve their performance. In accordance with this aim, Cr2(SO4)3, CrK(SO4)2.12H2O, (NH4)2SO4.Cr2(SO4)3, (CH3COO)3Cr, Cr(III)Cl3.6H2O, FeCl2, Fe(CH3SO3) compounds have been used as redox couple sources for catholyte and anolyte solutions, Spectroscopic Grafite (SpGr), commercial stack grafite (StGr) and Glassy Carbon (GC) have been used as carbon based electrodes. Various metal based (Ti, Pd, Au, RuIr deposited Ti, Ag, Pt, GrPt (Platinized Grafite))) electrodes have been also used. To examine the current density, potential and reduction and oxidation characteristics of redox couples, Cyclic Voltammetry and Electrochemical Impedance Spectroscopy analysis have been carried out. Deposition of catalysts metal have been characterized by X-Ray Diffraction Analysis and Scanning Electron Microscopy - Energy Dispersive X-Ray Spectroscopy methods. During the study, three electrode electrochemical cell system has been used for acquiring voltammetric and electrochemical data. Then a lab scale RFB that is built in the form of glass apparatus have been used to carry out to acquire charge, discharge, potential, current density data. Finally, a single cell RFB has been manufactured to simulate a commercial RFB System’s charge discharge characteristic. For the first setup it is observed that an all chromium RFB has still some rigid constraints on commercialization due to its limits on kinetics. So, the focus of this dissertation has been targeted to Iron-Chromium (Fe-Cr) batteries. Investigations on carbon-based electrodes are carried out in CH3SO3H, H2SO4, CH3COOH an HCl acid electrolytes SpGr electrode has been stand out to reduce and oxidize Cr. Except HCl, other acid electrolytes have shown poor electrochemical performance. In lab scale RFB set up, effect on catalysts on SpGr electrode and Cr(III)Cl3.6H2O with HCl has been examined. Effect of Ag catalysts demonstrated a boost on current density, however typical RFB charge/discharge curve has not been obtained. So to simulate the real performance and obtaining the characteristic charge/discharge profile a PP based single cell RFB has been manufactured. As a matter of fact, the expected outcome have been observed and a prototype of commercial RFB unit but cheaper compared to the equivalent, showed enhanced energy density results thanks to the cheaper electrolytes and redox couples. The results have been validated with EIS analysis. These results demonstrated that by using the compounds, which Turkey is one of the most producers, applicability and commercialization of a cost-effective large scale energy storage system is possible and promising.