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Anion exchange membranes (AEMs) contain cations that act as dipoles. The dipoles interact with each other and give rise to clustering in the AEM and this clustering can affect the ionic conductivity and mechanical properties of the polymer. Polymers designed to have dispersed cations can, when wet, have their cations cluster as the material undergoes an order-disorder transition at some temperature at which the system has enough energy to reorganize. Clustering is often unavoidable in AEMs and imposes a limit on the increase in conductivity that can be achieved by increasing IEC. Above a certain IEC AEMs do not show increased ionic conductivity only increased swelling on exposure to higher RH. Understanding these phenomena is essential to designing high performance AEMs. Here we propose an AEM based on a scalable random copolymer with rapidly deployed photo-crosslinking to lock the morphology in place to avoid cation clustering.

Conductivity of pure (air controlled) and air exposed hydroxide ion was compared using a unique sample preparation and conductivity measurements at controlled environment for a commercial FumasepÒ FAA anion exchange membrane. At 95%RH and 80°C, the membrane had conductivity value of 0.075 S/cm at the pure hydroxide form but reduced merely to 0.017 S/cm when the membrane was exposed to ambient CO2for 2 days. A comparative anionic (OH-, CO32-, and HCO3- forms) conductivity study showed the reduced ionic conductivity value by ¼ of its pure form; closed to HCO3- forms of the membrane. This indicated the formation of ionic mixture of CO32-, HCO3,- and residual OH-ions in the hydroxide form of the membrane when exposed to air. The hydroxide ions also showed a smaller ionic energy of activation when compared to other anions indicating a smaller ionic transport energy barrier.

Extensive transport and modeling studies have been performed on a series of polymers based on the benzyltrimethylamonium cations. We have created a realistic reactive model of solvated hydroxide that has interesting properties in the polymer matrix. In ordered di-block polymers we have strong theoretical evidence for a heterogeneous distribution of water across the channel. Fluoride is used as a non-reactive surrogate for hydroxide to increase the computational efficiency of transport calculations that can be performed. In addition to these studies we are discovering new base stable processable robust polymer backbones and cations. These bulky cations seem to dramatically affect the transport properties of the anions showing a VTF rather than an Arrhenius behavior with temperature.

Infrared study of water in a poly(ethylene-co-tetrafuloroethylene) anion exchange membrane at different level of hydration (%RH 0, 25, 50, 75 and 100) was performed using a Fourier transform infrared (FTIR) microscope. FTIR spectra showed at least two different states of water present in the membrane. The presence of both the non-hydrogen bonded water molecules at the lower hydration level and the hydrogen bonded water molecules at the higher hydration level, unambiguously, are altered with changing humidity.