Recast Nafion(R) 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 degrees 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(R)-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 degrees C. By contrast, the proton conductivity decreases with zirconia content for the composite membranes containing binary oxides at 120 degrees C. The composite membranes are tested in a 9-cm(2) commercial single cell at both 80 degrees C and 120 degrees C in humidified H-2/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 degrees C, 50% RH and 2 atm. (C) 2007 Elsevier B.V. All rights reserved.