The Mechanisms of Ion Transport through Ion Exchange Membranes for Use in Energy Storage Devices
Open Access
- Author:
- Cassady, Harrison Jasper
- Graduate Program:
- Chemical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 27, 2023
- Committee Members:
- Seong Kim, Professor in Charge/Director of Graduate Studies
Hee Jeung Oh, Major Field Member
Derek Hall, Outside Unit & Field Member
Bruce Logan, Major Field Member
Michael Hickner, Chair & Dissertation Advisor - Keywords:
- Ion Exchange
Membranes
Bipolar Membranes
Electrochemistry
Batteries
Redox Flow Batteries
Electrolysis
Mass Transport
Ion Exchange
Membranes
Bipolar Membranes
Electrochemistry
Batteries
Redox Flow Batteries
Electrolysis
Mass Transport
Ion Exchange
Membranes
Bipolar Membranes
Electrochemistry
Batteries
Redox Flow Batteries
Electrolysis
Mass Transport - Abstract:
- Ion exchange membranes are a class of charged polymeric separators with fixed charges that can selectively pass ions based on the sign of the charge carriers. These membranes are used in various industrial applications such as energy storage and conversion, electrolysis, electrodialysis, and desalination. This work seeks to elucidate the fundamental transport and thermodynamic phenomena of ions through ion exchange membranes, aiming to characterize and enhance the performance of a polysulfide-permanganate (pS-Mn) redox flow battery (RFB) and an electrolyzer designed to produce hydrogen and oxygen production from seawater. Additionally, fundamental factors that govern transport in bipolar membranes are described. Bipolar membranes (BPMs) were fabricated using poly(aryl piperidinium) as the anion exchange layer (AEL) and Nafion 212 as the cation exchange layer (CEL). The permeability of sodium chloride through these membranes was measured across a 0.5 M concentration differential. A flux differential of 76.3 ± 4.8 % was measured for the BPMs depending on the direction of the driving force. A model based on Fick's law and the Donnan equilibrium was developed and used to show that the flux differential results from changes in the ionic environment at the AEL–CEL junction due to differences in the ion diffusion coefficients and fixed charge concentrations of the two layers. The permeability of permanganate ions in Nafion 115 (N115) was measured to investigate the effects of co-ion transport in multi-ionic solutions. The permeability was measured with a 0.1 M NaMnO₄ concentration gradient, while the concentration of a supporting electrolyte was varied. Sodium hydroxide and sodium chloride were used as supporting electrolytes, with the concentration of sodium chloride ranging from 0.1 M to 4 M, and the concentration of sodium hydroxide ranging from 0.1 M to 10 M. A peak in the permanganate permeability was observed at a concentration around 1.1 M. To describe this peak, a model was developed from the electrochemical potential equivalency at thermodynamic equilibrium. The water uptake and salt sorption coefficients of sodium chloride and sodium permanganate were measured in N115 to provide the required inputs to the model. It was found that at low concentrations, the permanganate permeability is controlled by a reduction in the salt sorption coefficient due to the Donnan equilibrium. At high concentrations, the permanganate permeability is controlled by a reduction in ion diffusion coefficients within the polymer because of osmotic de-swelling. A survey of 23 commercially available cation exchange membranes was performed for the downselection of membranes for use in a pS-Mn RFB. The survey measured the permanganate flux across a 0.1 M concentration gradient as well as the membrane resistance in a 0.5 M sodium chloride solution. The membranes exhibited the characteristic flux/resistance trade-off observed in most classes of membranes. Cell performance data in a pS-Mn RFB was collected for three membranes from the survey. The coulombic, voltaic, and energy efficiency at low cycle counts aligned with the predictions from the survey results. The study also identified three membranes—the Fumapem F-930-RFS, Fumapem FS-715-RFS, and Aquivion E98-09S—that outperformed most other membranes in regard to their position on the flux-resistance trade-off curve, indicating them to be good candidates for further testing.