Electronic Theses and Dissertations

Identifier

6084

Date

2017

Date of Award

12-4-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Concentration

Organic Chemistry

Committee Chair

Tomoko Fujiwara

Committee Member

Abby L Parrill

Committee Member

Paul Simone

Committee Member

Xuan Zhao

Abstract

Anion exchange membrane fuel cells (AEMFCs) are an alternative renewable energy source with potential benefits including use of non-precious metal catalysts, facile electro-kinetics, and high power density. Despite these advantages, development of chemically robust and highly conductive anion exchange membranes (AEMs) is the great challenge. The properties of polymeric AEMs depend on many parameters, for example, backbone structures, morphology of membranes, and chemical stability of the ion transporting group. Therefore, all of these interconnected parameters have to be addressed and studied for AEM development. The objectives of this dissertation are 1) to develop durable membranes with high anion conductivity by cost effective materials and methods, and 2) to understand the structure-property relationship by designing polymer structures and membrane morphology. To achieve these goals, the presented research focuses on development of polystyrene (PS) based AEMs by the post-crosslinking method using the click reaction. The first work of this dissertation (chapter 2) was to establish a facile and effective AEM fabrication method. AEMs with optimized ion exchange capacity (IEC) and degree of crosslinking showed the improvement of electrochemical properties and fuel cell performance. Different PS architectures including block and random copolymers with the benchmark cation for AEM, benzyltrimethylammonium (BTMA), were designed and synthesized in our next step (chapter 3). The focus in this particular series was to study the effect of membrane morphology on ion conductive properties. Significant differences were observed between random and block copolymer based AEMs. The nano-scale ordered morphology of the block membranes led to satisfactory ion transport properties as well as improved durability of the membranes. Furthermore, the fuel cell test revealed that the block membranes maintained superior performance after multiple polarization curves in comparison with one of the best commercial AEMs (A201). The stability of cations is another crucial subject for AEM progress. Therefore, a novel AEM with phenyltrimethylammonium (PTMA) was fabricated from the PS based block copolymer, which was designed to avoid cation degradation through the elimination and nucleophilic substitution reactions (chapter 4). The preliminary data indicated that this novel AEM had higher thermal and chemical stability than the BTMA based AEM with similar structure.

Comments

Data is provided by the student.

Library Comment

dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.

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