National Research Council of Canada. NRC Institute for Fuel Cell Innovation
fuel cell; Nafion® membrane; proton conductivity; water sorption and transport; oxygen permeability
Nafion® 211 is the membrane of reference for many fuel cell users, but the literature on its properties is sparse. Unlike previous embodiments of Nafion® membranes, which are obtained by melt extrusion, Nafion® 211 is prepared by dispersion casting. This paper reports a range of properties obtained by ex situ and in situ characterization methods. Water uptake and proton conductivity are studied as a function of temperature and relative humidity. The extent of dimensional changes of as-received membranes upon hydration is found to be independent of thermal treatment. At 25 °C and 97% RH the maximum hydration number is ∼12. Absorption from liquid water and vapour are observed to be similar. Proton conductivity for Nafion® 211 is reported up 80 °C and as a function of relative humidity. At 80 °C, the conductivity increases from 0.0012 to 0.13 S/cm as RH is increased from 10 to 95%. The hydraulic permeability of Nafion® 211 is 2.4 × 10−16 m2 Pa−1 s−1 at 70 °C and the permeance is 8.8 × 10−12 m Pa−1 s−1. Oxygen solubility and the diffusion coefficient, studied using a solid state electrochemical cell, are 1.6 × 10−5 mol cm−3 and 1.04 × 10−6 cm2 s−1 at 30 °C, 100% RH, and 30 psi oxygen. Oxygen permeability is 1.71 × 10−11 mol cm−1 s−1 under similar conditions. In situ measurement of hydrogen crossover current is 1.2 mA/cm2 at 80 °C and 100% RH.