A flexible all-inorganic fuel cell membrane with conductivity above Nafion, and durable operation at 150 °c

The search for fuel cell membranes has focused on carbon backbone polymers, among which Nafion seems to best survive the most severe of the degradation mechanisms - attack by peroxide radicals. Less attention has been given to inorganic membranes because of their generally inflexible nature and lower conductivity, though some SiO₂-Nafion composites have shown improved properties. Nafion dominates, despite needing hydration, which then restricts operation to below 100 °C (so CO poisoning problems persist). Described herein is a low cost, flexible, and all-inorganic fiberglass reinforced gel membrane with conductivity exceeding that of Nafion at any temperature above 60 °C. Using Teflon fuel cells, maximum currents > 1 Acm^-2 and OCV of 1.03 V at 150 °C are demonstrated. No detectable loss of cell potential was observed over 24 h during 50 mAcm^-2 constant current operation at 120 °C while, at 150 °C and maximum power, the degradation rate is intermediate among other high conductivity H₃PO₄-PBI type membranes. The structure of the membrane is deduced, mainly from ²⁹Si solid state-NMR. The -115 ppm resonance, which is extreme for Q₄ Si(O) structures, identifies a zeolite-like SiO₂ network, which is "floppy". ³¹P and ¹H NMR establish nano-permeating H₃PO₄ as the source of the exceptional conductivity.