(Invited) Radiation-Grafted Anion-Exchange Membranes for Reverse Electrodialysis (RED): The Effect of Changing Functional Groups on Key Properties

Abstract

Radiation-grafted anion-exchange membranes (RG-AEM) are being developed at the University of Surrey in order to study a variety of chemistries and morphologies for use in a range of electrochemical applications. It is now clear that the ideal base films and grafted functional chemistries, required to fabricate the RG-AEMs, are different for each technology. Over the last decade or so, RG-AEMs with more than 100 different chemical configurations have been fabricated. Most of these have not been studied in detail as the focus was traditionally on RG-AEMs for use in alkaline membrane fuel cells where AEMs needed to have good stabilities in alkali. This has meant the focus was only on a small number of these chemistries. However, other electrochemical applications, such as electrodialysis (ED) and reverse electrodialysis (RED, a salinity gradient power technology) require AEMs to be operating in more neutral pH environments. This allows a wider range of chemistries to be used. For such applications, properties such as permselectivity and fouling resistance can be as important as ion conductivity. This presentation will provide a summary of recent RG-AEM developments at Surrey. A focus will be on the study of AEM chemistries for potential use in RED, with a study on the effects of crosslinking, head-group chemistry, and ion-exchange capacity. It has been found that despite being highly ionically conductive, non-crosslinked RG-AEMs have intrinsically low permselectivities and are prone to excessive levels of swelling in water (especially at high ion-exchange capacities). The incorporation of crosslinking can improve permselectivities, and lower swelling, but this often leads to detrimental drops in ion conductivity. Interestingly, the choice of head-group chemistry can have an effect on properties such as permselectivity. This research has been funded by EPSRC grants EP/M014371/1, EP/M022749/1, EP/R044163/1, and EP/T009233/1 along with EU Project SELECTCO2 (grant agreement 851441). Select recent references: R. Bance-Soualhi, M. Choolaei, S. A. Franklin, T. R. Willson, J. Lee, D. K. Whelligan, C. Crean, J. R. Varcoe, "Radiation-grafted anion-exchange membranes for reverse electrodialysis: a comparison of N,N,N',N'-tetramethylhexane-1,6-diamine crosslinking (amination stage) and divinylbenzene crosslinking (grafting stage)", J. Mater. Chem. A, 9, 22025 (2021) [CC-BY]. K. M. Meek, C. M> Reed, B. Pivovar, K.-D. Kreuer, J. R. Varcoe, R. Bance-Soualhi, "The alkali degradation of LDPE-based radiation-grafted anion-exchange membranes studied using different ex situ methods", RSC Adv., 10, 36467 (2020) [CC-BY]. T. R. Willson, I. Hamerton, J. R. Varcoe, R. Bance-Soualhi, "Radiation-grafted cation-exchange membranes: an initial ex situ feasibility study into their potential use in reverse electrodialysis", Sustainable Energy Fuels, 3, 1682 (2019) [CC-BY] L. Wang, X. Peng, W. E. Mustain, J. R. Varcoe, "Radiation-grafted anion-exchange membranes: the switch from low- to high-density polyethylene leads to remarkably enhanced fuel cell performance", Energy Environ. Sci., 12, 1575 (2019) [CC-BY].