Alkaline anion-exchange radiation-grafted membranes for possible electrochemical application in fuel cells

Abstract

This submission was created using the RSC Article Template (DO NOT DELETE THIS TEXT) (LINE INCLUDED FOR SPACING ONLY -DO NOT DELETE THIS TEXT)Vinylbenzyl chloride was grafted onto PVDF and FEP polymer films using the radiation-grafting methodology. Subsequent reaction with trimethylamine and ion-exchange with potassium hydroxide yields alkaline anion-exchange membranes that are capable of conducting hydroxide ions; such membranes may be suitable for use in low temperature direct methanol fuel cells for portable devices. The PVDF based materials underwent an undesirable degradation and were found to be less suitable for this class of membrane. FEPbased materials exhibited superior structural stability, conductivities up to 0.02 S cm -1 at room temperature, and good retention of ionexchange capacities when treated in water at 60°C.

Investigations of conductivity in FEP-based radiation-grafted alkaline anion-exchange membranes

“…This article extends our previous work which detailed: (1) synthetic protocol optimisation for the fabrication of RG-AAEMs, and (2) their chemical, structural, and thermoanalytical characterisation [26,27]. The conductivities of such AAEMs are now reported and are related to the initial grafting yields, ion-exchange capacities, and water contents.…”

“…However, these preliminary studies demonstrated that fully fluorinated FEP-derived AAEMs retained structural and ion exchange (chemical) integrity even when heated at 60°C for over 2500 h in water while open to air (and therefore carbon dioxide) [26].…”

“…[Note: the IECs in our previous synthetic studies [26,27] related to the IECs of the chloride-form anion-exchange membranes; the IECs in this study relate to the alkaline-form membranes to allow easier comparison with future fuel cell tests. ]…”

Prospects for Alkaline Anion‐Exchange Membranes in Low Temperature Fuel Cells

“…Recent studies in our materials chemistry laboratories at Surrey have concentrated on producing and optmising stable and conductive AAEMs in the same way (Scheme 4). Extensive solid-state NMR and vibrational spectroscopic studies showed that PVDF was an unsuitable base polymer for producing AAEMs due to lack of backbone stability when converted to the OHforms [76,77]; therefore, caution is advised with the use of the PVDF-based AEMs mentioned above if any trace of alkali is present. FEP was the base material of choice and was grafted with vinylbenzyl chloride (VBC); subsequent amination and alkali anionexchange yielded the desired AAEMs.…”

“…As a priority and to compliment ex situ stability measurements [77] (Figure 3), AAEMs must be evaluated in H 2 /O 2 , H 2 /air, and methanol/air fuel cells for several thousand hours to ensure adequate in situ membrane stability and assess the effect of and level of CO 2 2-/HCO 3 -formation. The effect of adding alkali to the methanol solution [56] must also be thoroughly investigated over long timescales.…”