Anion-exchange membranes for alkaline polymer electrolyte fuel cells: comparison of pendent benzyltrimethylammonium- and benzylmethylimidazolium-head-groups

Abstract

Radiation-grafted alkaline anion-exchange membranes (AAEM) containing pendent groups with either benzyltrimethylammonium (BTM) or benzylmethylimidazolium (BMI) functionality were successfully synthesised from the same base membrane and with identical ion-exchange capacities. The conductivity of the new BMI-AAEM is comparable to the BTM-benchmark AAEM. The fuel cell performance obtained with the BMI-AAEM was, however, significantly poorer due to in situ AAEM degradation. FT-Raman spectroscopic studies on the stability of the two head-groups at 60 C in aqueous potassium hydroxide (1 mol dm À3) indicates that the BMI-group is intrinsically less chemically stable in strongly alkaline conditions compared to the BTM-benchmark head-group. However, the stabilities of both head-groups are improved when treated at 60 C in lower pH aqueous carbonate and bicarbonate solutions (1 mol dm À3). Contrary to a portion of the prior literature, there appears to be no real advantage in using anion-exchange polymer electrolytes containing pendent imidazolium groups in highly alkaline systems.

Mechanical Characterization of Anion Exchange Membranes by Extensional Rheology under Controlled Hydration

“…The AEMs used in this study are the industrially produced polyetheretherketone (PEEK) reinforced Fumasep FAA-PEEK membrane from Fumatech, 26 an aminated tetramethyl polyphenylene (ATMPP) developed at Sandia National Laboratory, [27][28][29] and a radiation grafted poly(ethylene-cotetrafluoroethylene)-based quaternary ammonium AEM developed at the University of Surrey. 30,31 The three membranes were chosen as they have all been produced consistently in multi-gram quantities, the first under industrial quality control standards, the second in large research batches over multiple years, and the third from an industrially produced precursor film. This study compares the mechanical properties of these AEMs at a range of temperature and humidity conditions using a modified extensional rheometer system to simulate traditional tensile tests, and relates these properties to water uptake and swelling of the membranes.…”

International experts meet in Germany to discuss trends in anion exchange membranes

“…[5] A typical process involves the electron-beam irradiation of ETFE films in air, followed by reaction with vinylbenzyl chloride and a subsequent quaternisation process involving amines such as trimethylamine (to yield the target benzyltrimethylammonium head-groups). These radiation-grafted (RG)-AAEMs can have conductivities > 80 mS cm -1 at 80 °C and have been tested in hydrogen-oxygen APEFCs with peak power densities of > 500 mW cm -2 at temperatures of around 60 °C.…”

Reduction of the monomer quantities required for the preparation of radiation-grafted alkaline anion-exchange membranes

“…Simultaneous radiation-grafting is where the precursor polymers are irradiated whilst submerged in the grafting monomer solution of choice and pre-irradiation-grafting is where the polymer precursors are initially irradiated (commonly in air) and then subsequently treated with the grafting monomer solution. The AAEMs produced at the University of Surrey are based on the electron-beam pre-irradiation-grafting of poly(ethylene-co-tetrafluoroethylene) (ETFE) with vinylbenzyl chloride (VBC) monomer (previously used in large quantities and undiluted) before subsequent quaternization with a tertiary amine of choice [12][13][14]. VBC is both expensive and hazardous when used in large quantities (potential mutagen, acutely toxic on skin adsorption and ingestion, and very toxic to aquatic life): it is therefore vital to significantly reduce the quantity required during the grafting step.…”