A highly hydroxide conductive, chemically stable anion exchange membrane, poly(2,6 dimethyl 1,4 phenylene oxide)-b-Poly(vinyl benzyl trimethyl ammonium), for electrochemical applications

A chemically stable copolymer [poly(2,6 dimethyl 1,4 phenylene oxide)-b-poly(vinyl benzyl trimethyl ammonium)] with two ion exchange capacities, 3.2 and 2.9 meq g-1, was prepared as anion exchange membranes (AEM-3.2 and AEM-2.9). These materials showed high OH-conductivities of 138 mS.cm-1 and 106 mS.cm-1, for AEM-3.2 and AEM-2.9 respectively, at 60°C, and 95% RH. The OH-conductivity = 45 mS.cm-1 for AEM-3.2 at 60% RH and 60°C in the absence of CO2. Amongst the ions studied, only OH-is fully dissociated at high RH. The lower Ea = 10-13 kJ.mol-1 for OH-compared to F- ∼ 20 kJ.mol-1 in conductivity measurements, and of H2O from self-diffusion coefficients suggests the presence of a Grotthuss hopping transport mechanism in OH-transport. PGSE-NMR of H2O and F-show that the membranes have low tortuosity, 1.8 and 1.2, and high water self-diffusion coefficients, 0.66 and 0.26 × 10 cm2.s-1, for AEM-3.2 and AEM-2.9 respectively. SAXS and TEM show that the membrane has several different sized water environments, ca. 62 nm, 20 nm, and 3.5 nm. The low water uptake, "k = 9-12, reduced swelling, and high OH-conductivity, with no chemical degradation over two weeks, suggests that the membrane is a strong candidate for electrochemical applications.