A useful method of fabricating tailored functional polymers uses radiation grafting. This involves the treatment of inert polymer substrates with high energy radiation (e.g. electron beams), which introduces free radicals and/or peroxide groups into them. After this radiation- treatment, the “activated” polymer materials can then be reacted with vinyl group-containing monomers to produce grafted co-polymers. This can lead to the desired functional polymer materials either directly or after a further post-grafting functionalisation step. If desired, multiple functional monomers can be co-grafted onto the polymer substrates to give highly functionalised materials.
This technique can be used to make anion-exchange membranes (AEM), where positively charged groups are covalently bound to the grafted chains alongside the charge balancing counter anions. These radiation-grafted AEMs (RG-AEM) can then be ion-exchange into the desired anion conductive forms: e.g. Cl? for reverse electrodialysis cells, CO32? forms for CO2 electrolysis cells, or OH? for AEM-based fuel cells or H2 electrolysers. Apart from anion type, the RG-AEM parameters that can be tailored include: (1) substrate film type (e.g. ETFE or polyethylene films of varying crystallinity); (2) grafted chain chemistry (e.g. benzyltrimethylammonium, pyridinium, imidazolium); (3) thickness; (4) ion-exchange capacity; and (5) degree of crosslinking. If polymer powder substrates are used instead of film substrates, radiation-grafted anion-exchange ionomers (RG-AEI) can be formed instead of RG-AEMs. The RG-AEIs can be used to impart ion conduction and water retention in electrodes.
This talk will present the latest research into RG-AEMs and RG-AEIs at the University of Surrey (UK), which was conducted in collaboration with international partners such as the University of South Carolina (USA), Technion (Israel), ICCOM CNR (Florence Italy), the Technical University of Denmark (DTU), and the University of Sao Paulo and IPEN (Brasil). This research was funded by a mixture of UK Engineering and Physical Sciences grants (EP/M014371/1, EP/M022749/1, EP/R044163/1 and EP/T009233/1), EU Horizon 2022 (SELECTCO2 project, grant agreement 851441), and the Royal Society International Exchange Scheme grant (IES\R3\170134).
Recent Surrey-led 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);
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);
A. L. Gonçalves Biancolli, D. Herranz, L. Wang, G. Stehlikova, R. Bance-Soualhi, J. Ponce-Gonzalez, P. Ocon, E. A. Ticianelli, D. K. Whelligan, J. R. Varcoe, E. I. Santiago, "ETFE-based anion-exchange membrane ionomer powders for alkaline membrane fuel cells: a first performance comparison of head-group chemistry", J. Mater. Chem. A, 6, 24330 (2018);
L. Wang, M. Bellini, H. A. Miller, J. R. Varcoe, "A high conductivity ultrathin anion-exchange membrane with 500+ h alkali stability for use in alkaline membrane fuel cells that can achieve 2 W per square cm at 80 degC", J. Mater. Chem. A, 6, 15404 (2018).
L. Wang, J. J. Brink, Y. Liu, A. M. Herring, J. Ponce-Gonzalez, D. K. Whelligan, J. R. Varcoe, "Non-fluorinated pre-irradiation-grafted (peroxidated) LDPE-based anion-exchange membranes with high performance and stability", Energy Environ. Sci., 10, 2154 (2017).