A Raman Spectroscopic Study of Radiation-Grafted Anion-Exchange Membranes Containing Different Anions

Anion exchange membranes (AEM) are being developed for use in a variety of electrochemical energy systems, such as alkaline membrane fuel cells, AEM-based electrolysers, reverse electrodialysis (RED), and redox flow batteries (RFB). The AEMs used will contain a variety of anions, depending on the application. For fuel cells and electrolysers (H2 generating or CO2 conversion), then alkaline anions such as OH-, CO3 2-, and HCO3 - are important. For RED cells and RFBs, non-alkali anions such as Cl-, HSO4 -, and SO4 2- are more relevant. If an AEM is synthesised using a methyl iodide reaction, then monitoring the ion-exchange of the resulting "as-synthesised" I- forms to other forms, such as Cl-, is important as it is well known that it can be difficult to completely ion-exchange soft anions such as I- out of AEMs (particularly those containing aromatic cationic groups). This presentation will highlight some initial results obtained from an on-going Raman spectroscopic study of radiation-grafted AEMs (RG-AEM). This study was initiated to see if Raman spectro-microscopy can be used to identify the anion form of a RG-AEM by looking at the shifts and intensity changes of Raman peaks as a function of anion. The RG-AEMs will be made from either the grafting of vinylbenzyl chloride onto ETFE (followed by reaction with amines such as trimethylamine, imidazole and pyridine) or the grafting of alternative monomers such as vinylpyridine onto ETFE (followed by reaction with methyl iodide). The below Figure shows Raman spectra (Renishaw inVia Raman microscope: 785 nm laser, 1800 lines mm-1 grating, and x20 objective giving a Airy spot diameter of ca. 3 μm) of a RG-AEM made from the grafting of vinylpyridine onto ETFE films (with a final methyl iodide reaction) in both the I- and Cl- forms (three spectra each): . Figure 1