Evaluation of a sol-gel derived Nafion/silica hybrid membrane for polymer electrolyte membrane fuel cell applications - II. Methanol uptake and methanol permeability

Sol-gel derived Nafion/silica hybrid membranes were investigated as a poten tial polymer electrolyte for direct methanol fuel cell applications. Methan ol 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 s ilica content of approximate to 20 wt % showed a significant lower methanol permeation rate when immersed in a liquid methanol-water mixture at 25 and 80 degreesC. Methanol uptake from the vapor phase by the hybrid membranes appears similar to that of unmodified Nafion. Methanol diffusion coefficien ts, as determined from sorption experiments, were slightly lower in the hyb rid membranes than in unmodified Nafion. However, in direct permeation expe riments, significantly lower methanol vapor permeability was seen only in t he hybrid membrane with silica content of approximate to 20 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. (C) 2001 The Electrochemical Society.