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

• A flexible solid, all-inorganic, membrane for fuel cell MEAs.
• Conductivity above Nafion at T > 60 °C and stable to 150 °C.
• Conductivity mechanism same as for H3PO4 (anh).
• Fuel cell with I(max) >1 amp cm−2, and P(max) >200 mWcm−2 at 150 ºC, undegraded >24 hr.
• Structure, from 29Si MAS NMR, is “floppy” nanoporous silicalite-like gel with nanopermeating H3PO4.

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.

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