Nafion Nanocomposite Fuel Cell Membranes for Improved High Temperature Performance*

Proton exchange membranes represent an active area of fuel cell research. Current work seeks a membrane with excellent proton conductivity, minimal permeability of oxygen and fuel, and stable physical properties. At temperatures above 90 °C, traditional Nafion membranes experience decreased proton conduction, decreased water uptake, and softening. Although the performance is still being improved, addition of silica nanoparticles to Nafion membranes is known to improve conduction and water uptake at high temperatures. Recent work shows a new polymer nanocomposite system that stiffens repeatably and reversibly with increasing temperature via interfacial heterogeneous dynamics between a matrix polymer with low glass transition temperature (T_g) and high T_g polymer modifier adsorbed to silica nanoparticles. Studies were completed to investigate the applicability of this phenomena to Nafion using silane coupling agents to achieve improved high temperature performance. The effects of silica nanoparticle and grafted modifier concentration, and grafted chain structure and dynamics on Nafion nanocomposite structure and properties, particularly thermal stiffening, were studied.