An investigation of poly(imidazolium)s for alkaline energy storage and conversion devices

Most of the global energy demand is met using environmentally damaging and finite fossil fuel sources. Electrochemical energy conversion devices generating and using hydrogen fuel offer a solution which relies exclusively on renewable energy sources. However, implementation of such technologies has been stalled by high device cost. Alkaline energy conversion devices enable the use of cheaper and more environmentally friendly, non-perfluorinated ion conducting polymers. The development of these devices has been impeded by the low durability of organic materials in high pH conditions and the low mobility of hydroxide, limiting material conductivity. Poly(imidazolium)s have emerged as a highly durable, highly conductive materials and are the leading candidates for hydroxide conducting polymers. The focus of this thesis is the implementation of novel poly(imidazolium) synthetic routes for a greater understanding of the structure-property correlations. In Chapters 3, 4 and 5, the poly(imidazolium)s are prepared using an AB-type step growth polymerisation mechanism enabling precise control of functionalization and end group chemistry. In Chapter 3, a one-pot three-component reaction was developed for the synthesis of tetrasubstituted poly(imidazole)s. The reaction was modified in chapter 4 for the synthesis of a poly(imidazolium) with targeted macromolecular properties for implementation as an ionomer, into the catalyst layer. The poly(imidazolium) allowed for the investigation of ionomer-catalyst interactions and their impact on the hydrogen evolution and hydrogen oxidation reactions. The alkaline stability of poly(imidazolium)s was explored in chapters 5 and 6. Using the AB-type polymerisation method, the poly(imidazolium) end groups are defined in chapter 5 and the impact of reactive carbonyl end groups on main chain polymer alkaline stability is investigated. In Chapter 6, a series of imidazolium model compounds with varying N-functionalities were explored and the different methodologies available for alkaline stability investigation were discussed. This data was compared to the alkaline stability of analogous poly(imidazolium) materials. Through this work, a simple and modular synthetic route was established for poly(imidazolium)s, allowing for future systematic variation of polymer structure to be investigated. The structural variation and subsequent macromolecular properties can be correlated for the development of tuneable materials for specific applications.