Date of Award

2020

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Materials Science and Engineering (PhD)

Administrative Home Department

Department of Materials Science and Engineering

Advisor 1

Jiann-Yang Hwang

Committee Member 1

Stephen A. Hackney

Committee Member 2

Bowen Li

Committee Member 3

Song-Lin Yang

Abstract

High-performance ion exchange membranes with high ion exchange capacity (IEC), excellent mechanical properties, lower membrane resistance and superior ions conductivity were developed with chemical-induced polymerization in this work. Through a series of synthesizing experiments, structure characterization and properties testing for polyolefin-based cation exchange membrane (CEM) and anion exchange membrane (AEM), LDPE proved to be an optimized backbone material. The CEM with 57.5% styrene, 38.4% LDPE, 3% crosslinking degree and 1% initiator addition yield the highest IEC value (1.72 mol/g) and moderate burst strength. The 10% addition of styrene was found to enhance IEC of 57% to AEM. However, continually increase styrene leaded lower IEC due to the decreasing grafting degree of vinyl benzene chloride (VBC) on polyethylene.

The influence of fillers, such as surface-modified glass fiber (GF) and functionalized graphene oxides (GO), on thermal, mechanical and electrochemical properties of ion exchange membrane were investigated in this work by dynamic mechanical analysis, IEC and field emission scanning electron microscopes (FE-SEM), fourier-transform infrared spectroscopy (FT-IR) and electrochemical impedance spectroscopy. The addition of modified GF increases tensile strength, tensile modulus, storage modulus and interfacial adhesion of GF/CEM composite but degraded the strains. The composite with [3-(Methacryloxy) propyl] trimethoxy silane (3-MPS) modified GF obtained superior mechanical properties and interfacial adhesion, whereas the modified effect of triethoxyvinylsilane (TES) was inconspicuous. The addition of unmodified GF even had negative effects on GF/CEM mechanical properties. The FE-SEM showed that the GF treated by 3-MPS and poly(propylene-graft-maleic anhydride) (PP-g-MA) have better compatibility with the CEM matrix than 1,6 bis and TES treated GF. The FT-IR verified the strengthening effects from modified GF were attributed to the formation of Si-O-Si and Si-O-C bonds. The additions of modified GF in CEM positively influence water uptake ability but negatively on IEC. This section provided a way of strengthening GF/CEM composite.

The CEM doped with functionalized graphene oxides was verified to be significantly improved in IEC (21% higher) and membrane conductivity (326.7% higher) compare to the pristine CEM. The results also suggested that the improved effects of dual-functionalized GO on CEM properties are superior to the single functionalized GO. The coexistence of -PO3H, -SO3H in GO resulted in CEM possessed 7.8% higher IEC, 77.29% higher membrane conductivity and 43.56% lower activation energy than that with single functionalized GO. This work provides a new strategy for the design of high-performance IEM with excellent mechanical property, high IEC, high conductivity and low membrane resistance for application.

dissertation_Di_Huang_07302020__1_new.pdf (22546 kB)
revised dissertation

Available for download on Monday, December 20, 2021

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