Abstract
A major disadvantage of fossil fuels being the primary source of global energy is the negative effect that the burning of such fuels has on the planet. This is evident in factors including climate change. Reverse electrodialysis (RED) is an emerging membrane-based process for clean energy conversion. The technique works by utilising the transport of cations and anions through ion-exchange membranes (IEMs) to create an electrical current, via differences in chemical potential, when mixing salt solutions of different concentrations. The core components of a RED cell, and the largest factor affecting the performance and economic viability, are the IEMs. Recently, increased efforts have been made with regard to the preparation of IEMs and understanding the relationships between membrane properties and RED cell power performance. The work in this thesis has focused on the development of RED-focused IEMs by radiation induced grafting polymerisation (RIG). The RIG technique has been used to chemically modify commercially available polymer films to produce a large sample of IEMs targeted for application in RED. The IEM properties were experimentally determined and used as part of a literature recognised mathematical model to estimate the gross power densities that can theoretically be obtained by each IEM in a working RED cell. The results obtained for RIG IEMs contradicts the earlier notion that IEM permselectivity is of less significance than area resistance and indicate that a minimum permselectivity (≈ 90%) is required for RED IEMs. A trade-off relationship between the two properties is observed, rationalised by Donnan exclusion factors surrounding IEM water content. Chemical crosslinking was implemented into RIG methods to control excessive gravimetric water uptake (WU%). Linear tertiary diamine head-groups were used to produce crosslinked anion-exchange membranes (AEMs), with tetramethylhexanediamine (TMHDA) head-group yielding theoretical gross power densities of 3.42 W m-2 for single IEM RED model calculations and 1.89 W m-2 for AEM/CEM pair calculations (paired with literature SPEEK 65 CEM). Crosslinked CEMs were produced via chemical crosslinking by divinylbenzene (DVB) and bis(vinylphenyl)ethane (BVPE) was implemented into the RIG method, which resulted in cation-exchange membranes (CEMs) yielding theoretical gross power densities of 5.55 and 5.99 W m-2 respectively, for single IEM RED model calculations and 2.81 and 2.71 W m-2 for AEM/CEM pair calculations (paired with commercial Neospeta® AFN AEM).