Polyethylene Based Ion Conductors

Author:

Kim, Hyung Kyu

Graduate Program:

Materials Science and Engineering

Degree:

Master of Science

Document Type:

Master Thesis

Date of Defense:

March 15, 2012

Committee Members:

Dr T C Mike Chung, Thesis Advisor/Co-Advisor
Serguei Lvov, Thesis Advisor/Co-Advisor
Dr Micheal A Hickner, Thesis Advisor/Co-Advisor

Keywords:

Proton exchange membrane
fuel cells
polyethylene
anion exchange membrane
electrolytic cell

Abstract:

In this thesis, new ion conductive polymeric membranes were synthesized and studied for potential fuel and electrolysis cell applications. Polyolefin was used as the polymer backbone that provides the membrane with a stable and hydrophobic matrix, and some ionic groups were introduced in random or graft microstructure fashion to provide ionic channels for conductivity. The random copolymers were prepared by direct copolymerization and the graft copolymers were obtained by graft-onto reaction. In Chapter 1, general background and theory for ion conductive membrane are introduced. It covers the principles of fuel cells, synthesis of functional polyolefins, and fabrication of membranes. In Chapter 2, new cationic exchange membranes are discussed, which is the main topic of this thesis. This chapter covers the procedures to prepare new polyethylene-graft-poly(arylene ether sulfone) graft copolymers, their structure characterization and membrane fabrication, and evaluation for fuel cell applications. Some PE-based PEMs show promising results with the desirable properties for proton exchange membrane and direct methanol fuel cells. Chapter 3 discusses a new polyethylene-based anionic exchange membrane, containing ammonium chloride (NR3+Cl-) groups and cross-linkers. The chemistry was successfully developed to prepare a broad range of copolymer compositions for a systematic structure-property relationship study. Some cross-linked anionic membranes, with high IEC value and moderate water swelling, outperform all commercial membranes with exceptionally high ionic conductivity. In Chapter 4, conclusion and future work are included with the suggestions for further developing this class of polyolefin-based membranes. At the end of the thesis, appendix are provided, related to more detail information about measurements including proton conductivity and methanol permeability. Overall, this thesis is devoted to develop a new chemical route to prepare ion conductive polyolefins (PE, PP, etc.) that are semi-crystalline, ductile, good chemical stability, excellent hydrophobicity in the matrix, and cost-effective. The resulting polyolefin-based ion exchange membranes may show advantages in other areas, including electrodialysis, desalination etc.