Hybrid polyelectrolytes based on stable sulfonated polynorbornene with higher proton conductivity and lower methanol permeability

Abstract

We report preparation of hybrid cross-linked proton exchange membranes (PEMs), which are synthesized from sulfonated copoly(norbornene)s bearing sultone pendant (SPBN) and a zwitterionic silica containing sulfonic acid and ammonium groups, 3-[[3-(triethoxysilyl)-propyl]amino]butane-1-sulfonic acid (TPABS), using a sol–gel process. As these membranes are well processed as self-supporting film, they show high stabilities, proton conductivity and low methanol permeability. Reported SPBN/TPABS-50 (50 wt % of TPABS to SPBN in the matrix) shows the best performance with proton conductivity of 6.34 × 10−2 S cm−1, methanol permeability of 3.64 × 10−7 cm2 s−1, ion-exchange capacity value of 1.21 mequiv g−1 and comparable selectivity parameter of 1.74 × 104 S cm−3 s. While the membrane electrode assembly (MEA) is fabricated using the SPBN/TPABS-50 as PEM, the open circuit voltage of SPBN/TPABS-50 at 1.0 M methanol (80 °C) and its power density of the devices are 0.563 V and 50.2 mW cm−2, respectively, though which is lower than that of Nafion117 (124.2 mW cm−2). The new designed cross-linked membranes can thus be a promising candidate to satisfy the requirements of PEMs for direct methanol fuel cells, especially the simple and low cost preparation of the membranes.