ZrO₂-SiO₂/Nafion^® composite membrane for polymer electrolyte membrane fuel cells operation at high temperature and low humidity

Recast Nafion^® composite membranes containing ZrO₂-SiO₂ binary oxides with different Zr/Si ratios are investigated for polymer electrolyte membrane fuel cells (PEMFCs) at temperatures above 100 °C. Fine particles of the ZrO₂-SiO₂ binary oxides, same as an inorganic filter, are synthesized from a sodium silicate and a carbonate complex of zirconium by a sol-gel technique. The composite membranes are prepared by blending a 10% (w/w) Nafion^®-water dispersion with the inorganic compound. All composite membranes show higher water uptake than unmodified membranes, and the proton conductivity increases with increasing zirconia content at 80 °C. By contrast, the proton conductivity decreases with zirconia content for the composite membranes containing binary oxides at 120 °C. The composite membranes are tested in a 9-cm² commercial single cell at both 80 °C and 120 °C in humidified H₂/air under different relative humidity (RH) conditions. Composite membrane containing the ZrO₂-SiO₂ binary oxide (Zr/Si = 0.5) give the best performance of 610 mW cm^-1 under conditions of 0.6 V, 120 °C, 50% RH and 2 atm.