Solar Thermal Fuels for Automotive Applications

Solar thermal fuels are an emerging class of materials containing photochromic molecules (such as azobenzene) capable of harvesting, storing, and releasing solar energy. This thesis contains an investigation into the solar energy storage properties of azobenzene-based polymers for automotive application. The synthesis of azobenzene containing monomers and polymers, as well as the characterisation of the energy storage and release, thermal and optical properties is presented. The design and development of the polymer structure is discussed along with the method for creating polymer films. The films are used to evaluate the performance of the polymers as STF materials in the solid-state and demonstrate their viability for use under “real-world” conditions. It was found that the energy density of the polymer system was limited by the population of the cis isomer at the photostationary state. This arises due to the overlap of absorption bands for the trans and cis isomers and presents an intrinsic limitation on the energy density of the system. It was found that introducing an alkoxy group between the azobenzene moiety and the ester group led to a change in the electronics of the system resulting in changes to the absorption properties and in turn a higher photostationary state. This then corresponded to a significantly increased energy density. The presence of the alkoxy group also changed the physical properties of the polymer, most notably a decrease in the glass transition temperature, Tg. A decrease in the Tg can indicate an increase in the limited free volume of the system, increasing the photostationary state and rate of photoisomerisation. Consequential in the solid-state, thin films of this material reach photostationary states comparable to that observed in solution. This investigation highlights the importance of understanding the structure-property relationships in STFs, thereby providing a direction for optimisation for real-world energy storage applications