Analysis of mechanism of Nafion® conductivity change due to hot pressing treatment

In previous work, the authors observed that multiple hot-pressing cycles of Nafion 212 prior to Proton Exchange Membrane Fuel Cell (PEMFC) operation was found to result in significant performance gains. In order to further explore this effect, Nafion 212 samples were subjected to various thermal treatments and then to various analytical techniques in order to probe whether changes to the membrane contributed to these performance gains in a substantial way. Electrochemical Impedance Spectroscopy (EIS) measurement sought to validate that the treatment caused a proton conductivity change. Thermogravimetric Analysis (TGA) and Fourier Transform Infrared Spectroscopy (FTIR) measurements were implemented to determine whether chemical changes in the membrane occurred. Results suggest that the hot pressing treatment causes a significant effect in the electrical properties of Nafion 212, however the physical change that occurs in the polymer is not chemical in nature. Further analysis attempts to support the idea that the change in proton conductivity is due to water channel reconfiguration in the membrane, activated by elevated temperature and compressive stress at the glass transition temperature of the Nafion 212.