The addition of metal oxide particles to recast Nafion membranes has been found to improve fuel cell performance, particularly at high temperatures and reduced humidity.[1] Operation under these conditions is desirable for enhanced CO tolerance and heat management, yet often causes membrane drying, reducing proton conductivity and over-all cell performance.

The specific qualities of composite membranes that lead to enhanced cell performance should be identified to further engineer improvements. Membrane mechanical and water-sorption properties are examined here and comparisons are made between Nafion and Nafion/Titania composite membranes. Special attention is paid to membrane behavior in confined spaces (as encountered in a tightly sealed fuel cell) in which dimensional swelling and water uptake might be inhibited.[2] Nafion/Titania composite membranes are found to have a slightly higher swelling pressure, consistent with a slightly higher Young's modulus. The interplay of thermodynamics and kinetics in Nafion water sorption—sulfonic acid solvation, concentration-driven and concentration-dependent diffusion, elastic chain stretching and viscoelastic chain relaxation and rearrangement--will be examined in light of measured mechanical properties of the membrane.

1. Yang, C., et al., A comparison of physical properties and fuel cell performance of Nafion and zirconium phosphate/Nafion composite membranes. Journal of Membrane Science, 2004. 237(1-2): p. 145-161.

2. Satterfield, M.B., et al., Mechanical Properties of Nafion and Titania/Nafion Composite Membranes for PEM Fuel Cells. J. Polymer Science B: Polymer Physics, 2006. In Press.