Mass spectrometry to quantify and compare the gas barrier properties of radiation grafted membranes and Nafion®

• Gas permeability of radiation grafted membranes was measured by mass spectrometry.
• Radiation grafted membranes show much better gas barrier properties than Nafion 212.
• The effects of water content, graft level, comonomers and temperature were examined.
• A physical model explains experimental results and gas transport mechanism.
• Deterioration of gas barrier properties was monitored in situ.

This study describes a method using mass spectrometry (MS) to quantify the gas barrier properties of different classes of ionomer membranes and the base film used in radiation grafted membranes for polymer electrolyte fuel cells. The effects of relative humidity (RH), temperature and graft level are investigated for different types of radiation grafted membrane with dissimilar chemical compositions. The results show that the radiation grafted membranes and Nafion® 212 share the same trend of increasing gas permeability with RH, while the ETFE base film does not show RH dependency. With addition of nitrile-containing comonomer units in the grafted chains, the permeability of reactant gases in the membranes can be remarkably reduced. On the basis of experimental results, a physical model is proposed to describe the effect of water contents on the gas transport in the radiation grafted membranes and to explain the effect of graft level on gas barrier properties and the difference of gas barrier properties at high and low hydration levels between Nafion® membranes and radiation grafted membranes. Using helium as a tracer, the deterioration of the gas barrier properties of the radiation grafted membrane during an accelerated stress test at open circuit voltage (OCV) is recorded in situ.

The gas permeability of ETFE based radiation grafted membranes was measured in a fuel cell set-up as a function of relative humidity (RH) using mass spectrometry. The grafted styrene sulfonic acid chains hinder the gas transport across the membrane in the low RH region, but significantly enhance diffusivity in the high RH region. Figure optionsDownload high-quality image (172 K)Download as PowerPoint slide