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Abstract: 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 610mWcm−1 under conditions of 0.6V, 120°C, 50% RH and 2atm. [Copyright &y& Elsevier]

Abstract: Hydrophilic SiO2 particles are added to the catalyst layer of a fuel cell membrane–electrode assembly (MEA) to improve wettability and performance at low-humidity conditions. The SiO2 added MEAs are prepared by spraying technique and the contact angle is measured by the sessile drop method. The effects of SiO2 additions of 0, 20, 40 and 60wt.% (based on Pt/C) are investigated for various relative humidity levels in the anode and the cathode. The increased wettability of the cathode catalyst layer exerts an adverse effect on cell performance by causing flooding; this result demonstrates the hydrophilicity of SiO2. With 40wt.% addition of SiO2 to the anode catalyst layer, the current density at 0.6V and 0% relative humidity of the anode is 93% of that at 100% relative humidity. By comparison, the performance of a cell using a MEA with no added SiO2 is only 85% of that at 0% relative humidity. A MEA with SiO2 addition in the anode gives a higher performance at 60% relative humidity of the cathode than one with an undoped MEA. Increased wettability of the anode catalyst layer caused by SiO2 addition renders it easy to absorb water from back diffusion. [Copyright &y& Elsevier]