Preparation and applications of polymer immobilised ionic liquids for electrochemical applications

Abstract

Chapter 1 introduces and explores the concept of ionic liquids and polymer-immobilised ionic liquids as functional materials for alkaline anion exchange fuel cells (AAEMFCs) and catalysis. Chapter 2 details the preparation of a norbornene-based monomer library which has been used to prepare and test a series of polymer formulations for physical and electrochemical testing, with the aim of identifying suitable membranes for fuel cell and related electrochemical technology. The most conductive AAEMs prepared in utilised a diethylene glycol (DEG) cross-linker and had an ionic conductivity of 27.2-31.0 mScm-1 at 80 °C. This chloride conductivity corresponds to a hydroxide conductivity of 71-81 mScm-1 at 80 °C – these values were estimated using an experimentally tested ion mobility conversion factor. This chapter also covers the development of a suitable accelerated stability study for anion exchange membrane degradation in hydroxide conditions monitored by NMR spectroscopy. The two ionic monomers prepared were found to be chemically stable in alkaline conditions at 80 °C over 696 hours. Polyoxometalate poly(ionic liquid) phase catalysts (POM@PIILP) were prepared utilising a styrene polymer architecture in chapter 3 with the aim of preparing new catalysts for biomass transformation. An initial screening was carried out in order to identify the most efficient catalysts to take forward and optimise in terms of catalyst loading, operating temperature and catalyst recyclability. Lead catalysts were identified and were capable of 90-99% conversion with respect to the substrate, furfuryl alcohol, and achieved 100% selectivity to product, nbutyl levulinate, in 2 hours. However, issues with catalyst recyclability were encountered; preliminary poisoning experiments suggested that deactivation of the surface reduced catalytic activity. Chapter 4 introduces a new technology to expand upon the Doherty’s group expertise in ionic liquid synthesis in the form of materials suitable for 3D printing by digital light processing technology. In this chapter imidazolium-based ionic liquid monomers were prepared, and suitable acrylate-based cross-linkers were used to formulate photopolymer resins. Screening of these resins was carried out using a bespoke UV-LED system and then suitable materials were 3D printed using a digital light processing (DLP) UV photopolymer printer. The resultant ion exchange membranes were then assessed in terms of their ionic conductivity, ion exchange capacity and mechanical integrity as anion exchange membranes in a similar manner to the membranes prepared in Chapter 2. The polymers were found to have a chloride ionic conductivity of 19-31 mScm-1 at 80 °C, which equates to an estimated hydroxide conductivity of 50-81 mScm-1 .