Cho, Kyu Taek
M.S. (Master of Science)
Department of Mechanical Engineering
Storage batteries--Materials; Oxidation-reduction reaction
The redox flow battery (RFB) stores energy in the form of oxidized and reduced electro-active chemical species which are stored externally to the battery cell, allowing the RFB to have benefits of decoupled control and design of energy and power. Therefore, the RFB is getting intensive attention as one of the most promising and cost-effective systems to store large amounts of energy typically from renewable resources. However, even with the big benefits of the RFB system, the full application of RFB could not be achieved due to the challenging issues such as high system cost and safety issues associated with use of toxic and corrosive chemicals. The motivation for this research is to develop an eco-friendly and cost effective flow battery to solve the key issues of conventional RFB. The cost is expected to be reduced significantly by eliminating the expensive component of the system i.e. membrane. By eliminating the membrane, the cost can be lowered by about 40% and also other issues related to membrane like contamination (increase of ohmic resistance) can be minimized. In order to develop an eco-friendly system, aqueous Iron-ion solution was used because of its low toxicity, low cost and availability. Especially, this research focuses on finding an optimum structure of cell components for a membrane-less redox flow battery to restrict the overflow of the electrolyte to the other side (i.e. H2 side) of the cell and thus minimize decay of open circuit voltage (OCV). The overflow (i.e. OCV) control was made with carbon porous media in the cathode side which were coated with various contents of Teflon. Effects of Teflon impregnated in carbon porous media on liquid permeability and porosity were investigated in ex-situ test, and the results were compared with in-situ full cell test. It was found that carbon porous media with Teflon content of 12 wt.% was the best to minimize overflow of electrolyte and maximize the cell performance which is similar to that of the membrane system. Especially, effect of concentrations on impedance on the cell were compared, and change of ohmic resistance was negligible for membrane-less system, while the change was significant for membrane system, which is the main reason for cell performance decay in the highly concentrated electrolyte or long cyclic test. In this study, the critical design parameters were defined, and benefits of membrane-less system was clearly observed. The results of this study can be utilized as a guideline for developing membrane-less RFB system.
Kolli, Jayanth, "Optimum structure of cell components for a membrane-less iron-ion/hydrogen redox flow battery" (2016). Graduate Research Theses & Dissertations. 4215.
x, 60 pages
Northern Illinois University
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