Sol-gel derived Nafion®/silica hybrid membranes were investigated as a potential polymer electrolyte for fuel cell applications. Membrane proton conductivity and water content were measured as a function of temperature, water vapor activity, and silica content. The hybrid membranes have a higher water content at 25 and 120°C, but not at 150 and 170°C. Despite the higher water content, the proton conductivities in the hybrid membranes are lower than, or equal to, that in unmodified Nafion membranes under all conditions investigated. The proton conductivity of the hybrid membrane decreases with increasing silica content under all conditions.

Sol-gel derived Nafion/silica hybrid membranes were investigated as a potential polymer electrolyte for direct methanol fuel cell applications. Methanol uptake and methanol permeability were measured in liquid and vapor phase as a function of temperature, methanol vapor activity, and silica content. Decreased methanol uptake from liquid methanol was observed in the hybrid membranes with silica contents of 10 and 21 wt %. The hybrid membrane with silica content of Ϸ20 wt % showed a significant lower methanol permeation rate when immersed in a liquid methanol-water mixture at 25 and 80°C. Methanol uptake from the vapor phase by the hybrid membranes appears similar to that of unmodified Nafion. Methanol diffusion coefficients, as determined from sorption experiments, were slightly lower in the hybrid membranes than in unmodified Nafion. However, in direct permeation experiments, significantly lower methanol vapor permeability was seen only in the hybrid membrane with silica content of Ϸ20 wt %. Based on these results, Nafion/silica hybrid membranes with high silica content have potential as electrolytes for direct methanol fuel cells operating either on liquid or vapor-feed fuels.

In our last paper it had been implied that the presence of Pt on the cathode was more essential for membrane degradation. In this paper both effluent analysis and X-ray CT study have been done for the further understanding of membrane degradation. These studies support that the presence of Pt on the cathode is more essential for membrane degradation. Second purpose of this paper is to report the influence of electrocatalyst, GDL and types of membranes on membrane durability at open circuit voltage, i.e. OCV. It was confirmed that membrane was much less degraded on OCV test when using Asahi Kasei Advanced Membrane or using Pt:Co alloy as electrocatalyst. These results imply that the problem of membrane degradation during higher cell temperature operation under low humidification can be overcome by the further improvement of both membrane and electrocatalys

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