| Author: | Ma, Yining |
| Title: | Experimental investigations of membrane structure and transport characteristics and their applications in vanadium-air redox flow batteries |
| Degree: | M.Sc. |
| Year: | 2020 |
| Subject: | Storage batteries -- Materials Energy storage Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Mechanical Engineering |
| Pages: | vi, 51 pages : color illustrations |
| Language: | English |
| Abstract: | All-vanadium redox flow battery (VRFB) with its independently tunable power and energy storage capacity is believed to be one of the most promising candidates for practical applications and has drawn ever-increasing attentions. However, its worldwide deployment is still being greatly hindered by its low energy density as it utilizes two electrolyte tanks in the system, which greatly increases the system volume and weight. Hence, to attain a higher system energy density, the vanadium/air redox flow battery (VARFB), replacing one electrolyte tank in the VRFB with the ambient air, has been proposed and extensively studied. Such a change not only reduces the total volume of the system, but also results in a higher theoretical voltage (1.49V vs. 1.26V), which hence remarkably boosts the system energy density. In a flow cell, a proton exchange membrane, sandwiched between a thermally treated graphite felt (as negative electrode) and a conventional carbon-supported platinum coated carbon paper (as positive electrode), is to provide the ion channels for proton migration, but to alleviate the cross-contamination between the liquid electrolyte and gaseous oxygen/air. Hence, the proton exchange membrane, as a key component, plays a key role in determining the battery performance. The primary objective of this thesis is to study the effects of membrane structure and transport properties on the battery performance. A series of commercial Nafion membranes with a varied thickness from 25.4μm to 183μm have been characterized, compared and discussed. It is found that the membrane with the largest thickness (183 μm, Nafion 117) shows the highest water uptake of 22% and ionic conductivity of 35.09 mS cm-1 among the four membranes evaluated. While, the water uptake of the thinnest membrane (25.4 μm, Nafion 211) is as low as 12% with an ionic conductivity of 15.95 mS cm-1. Furthermore, the vanadium-ion crossover rate of the 183-μm-thick membrane (1.72 mol cm-2 h-1) is significantly lower than that of the 25.4-μm-thick one (5.11 mol cm-2 h-1), thereby resulting in the longest self-discharge duration of 39.9 h. In addition, it is also demonstrated that the flow cell assembled with a 183-μm-thick membrane, owing to its appropriate balance between ionic conductivity and vanadium-ion crossover rate, results in a peak power density of 283 mW cm-2 and an energy efficiency of 50.5% at room temperature. |
| Rights: | All rights reserved |
| Access: | restricted access |
Files in This Item:
| File | Description | Size | Format | |
|---|---|---|---|---|
| 5233.pdf | For All Users (off-campus access for PolyU Staff & Students only) | 5.93 MB | Adobe PDF | View/Open |
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