Poly(terphenylene) Anion Exchange Membranes: The Effect of Backbone Structure on Morphology and Membrane Property

A new design concept for ion-conducting polymers in anion exchange membranes (AEMs) fuel cells is proposed based on structural studies and conformational analysis of polymers and their effect on the properties of AEMs. Thermally, chemically, and mechanically stable terphenyl-based polymers with pendant quaternary ammonium alkyl groups were synthesized to investigate the effect of varying the arrangement of the polymer backbone and cation-tethered alkyl chains. The results demonstrate that the microstructure and morphology of these polymeric membranes significantly influence ion conductivity and fuel cell performance. The results of this study provide new insights that will guide the molecular design of polymer electrolyte materials to improve fuel cell performance

Durable Sulfonated Poly(arylene sulfide sulfone nitrile)s Containing Naphthalene Units for Direct Methanol Fuel Cells (DMFCs)

Sulfonated poly­(arylene sulfide sulfone nitrile)­s (SN) were synthesized to investigate the effects of naphthalene units in the polymer backbone on membrane properties. The small and planar naphthalene in the main chain reduced interdomain distance, as confirmed by molecular simulations and small-angle X-ray scattering patterns. The SN polymer membranes exhibited excellent chemical and mechanical properties, better than those of their phenylene counterpart (SP). In particular, the water uptake and swelling ratio of the SN membranes were much lower than those of the SP membranes. Furthermore, the SN membranes exhibited a greatly reduced methanol permeability ((9–17) × 10^–8 cm² s^–1) compared to Nafion 212 (330 × 10^–8 cm² s^–1) at 30 °C in 10 M methanol. Moreover, sulfide- and naphthalene-based chemical structure of the SN membranes enhanced their DMFC single cell performance and long-term stability during fuel cell operation

Durable Sulfonated Poly(benzothiazole-<i>co</i>-benzimidazole) Proton Exchange Membranes

Two series of random sulfonated poly­(benzothiazole-<i>co</i>-benzimidazole) polymers (sPBT-BI) with 70% and 60% degree of sulfonation were evaluated as proton exchange membranes. sPBT was also prepared for a comparative study. The mechanical properties of sPBT-BI were greatly enhanced by incorporation of benzimidazole (BI); sPBT-BI70-10 showed a tensile strength of 125 MPa and elongation at break of 38.9%, an increase of 56.5% and 145%, respectively, compared with sPBT. The solubility, dimensional stability, thermal properties, and oxidative stability of sPBT-BI were also improved. The ionic clusters of sPBT-BI membranes in both AFM phase images and TEM images became narrower with increasing amounts of BI while containing the same molar amount of sulfonic acid groups. This resulted in lower dimensional swelling and higher mechanical strength, but the proton conductivity decreased. However, high proton conductivity was achieved by incorporating an appropriate content of BI. PEMFC H₂/air single cell performances and durabilities were improved by incorporation of 5% of BI units in sPBT

Sulfonated Poly(arylene sulfide sulfone nitrile) Multiblock Copolymers with Ordered Morphology for Proton Exchange Membranes

Ordered morphologies in disulfonated poly­(arylene sulfide sulfone nitrile) (SPSN) copolymers were generated via thermal annealing followed by multiblock copolymer synthesis. While SPSN random copolymers (R-SPSN) showed featureless morphologies, the SPSN multiblock copolymers (B-SPSN) exhibited cocontinuous lamellar morphologies with a center-to-center interdomain size of up to 40 nm. In spite of the well-ordered, interconnected hydrophilic domains, the water self-diffusion coefficient (e.g., <i>D</i> = (0.7–2.0) × 10^–10 m² s^–1) and proton conductivity (e.g., σ = 0.16–0.20 S cm^–1 in deionized water at 30 °C) through B-SPSN were lower than those of the corresponding R-SPSN (e.g., <i>D</i> = (3.5–3.9) × 10^–10 m² s^–1 and σ = 0.21 S cm^–1) due to the relatively lower water uptake of the B-SPSN after thermal annealing. The reduced water uptake of B-SPSN was beneficial to reduction of peroxide degradation rate. Thermal annealing produced significant gains in morphological ordering and finer control over desired membrane properties for proton conduction applications