Synthetic design and development of proton conducting polyphenylenes for electrochemical energy conversion devices

Date created: 
Polymer electrolyte membranes
Cation exchange membranes
Fuel cells

Approximately 10% of the global energy demand is currently satisfied by renewable resources. To meet the United Nations’ 2015 climate change target, this value must shift to upwards of 50% before 2030. Electrochemical energy devices offer an array of solutions which may complement or enhance current (non)renewable energy technologies. Unfortunately, mass-adoption of such devices is to date impeded by their prohibitive costs and poor lifetimes. A major contributor to these deficits is the solid polyelectrolyte membrane, which is used internally as both an electrical resistor and highly selective ion transporter. Despite preparation from controlled substances, with nominally toxic degradation by-products, perfluorinated structures remain the technological standard in electrochemical energy devices. The focus of this thesis is the development of hydrocarbon-based, fluorine-free polymers which may collectively exhibit comparable or superior performance to those possessing perfluorinated structures. Sulfonated, phenylated poly(phenylene)s are prepared exhibiting precisely controllable degrees of functionalization, incorporating aryl spacer units with increasing size. This serves to both decrease membrane hydrophilicity, and increase electrochemical performance both ex-situ, and in-situ when integrated into hydrogen fuel cells. Polymer durability, with emphasis on the latter is investigated. The demanding thermal polymerization conditions used to prepare this class of materials are addressed through development of novel, rapid microwave-assisted methods. Thorough material characterizations are performed to assess the advantages and deficits over traditional, thermal synthetic methodologies. Concurrently, materials are prepared in larger batches to investigate their scalability. Poor hydrocarbon membrane water sorption, structural integrity, and chemical stability limit their application in electrochemical devices. The incorporation of molecular branching into polymers is evaluated as a facile means of universally improving these properties. The materials reported show steady advancements in their stabilities and membrane properties, which culminates in ever-increasing and best-in-class performance when assessed within fuel cells.

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This thesis may be printed or downloaded for non-commercial research and scholarly purposes. Copyright remains with the author.
Steven Holdcroft
Science: Department of Chemistry
Thesis type: 
(Thesis) Ph.D.