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S8.6.1

Hybrid Proton-Carrier Polymer Composites for High-Temperature FCPEM Applications F. J. Pern,1 J. A. Turner,1 and A. M. Herring2 1 National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401 2 Department of Chemical Engineering, Colorado School of Mines, Golden, CO 80401

ABSTRACT Hybrid proton-carrier polymer composites were fabricated in an effort to develop highperformance high-temperature proton exchange membranes (PEMs) for fuel cell applications in the 100o–200oC range. The solution-cast hybrid membranes comprise a polymer host and a SiO2based proton-carrier composite that was synthesized via sol gel approach using a functional silane and tetraethoxysilane (TEOS) in acidic conditions. The primary H+-carrying component was either a heteropoly silicotungstic acid (STA) or a sulfonic acid (SFA) that was thermooxidatively converted from a mercapto (-SH) group. The embedding level of STA on the silanemodified SiO2 sol gel composites was strongly affected by the presence and the functional group of the silane. Ion exchange capacity (IEC) of the water-washed, SiO2-based STA and SFA proton-carrier composite powders is in the range of 1.8–3.5 mmol/g, two to three times higher than that for Nafion 117 (0.9 meq/mol). A glycidylmethacrylate-type copolymer, PEMAGMA, which is stable up to ~225oC, was able to produce mechanically robust and flexible hybrid membranes. Upon curing, the PEMAGMA composite membranes showed a ~75% gel under the present formulation and retained the "free" STA effectively with slight loss when extracted in an 85oC water. The W12-STA-containing PEMAGMA membranes followed the weight loss trends of water from STA and the SiO2-based sol gel composite, showing a 10 wt% loss at 150oC and a 15 wt% loss at 225oC. Fuel cell performance tests of the preliminary films gave a Voc in the 0.85–0.93 V range, but a low current density of