Mechanical response of thermally annealed Nafion thin films
Bradley R. Frieberg, Kirt A. Page, Joshua R. Graybill, Marlon L. Walker, Gery R. Stafford, Christopher L. Soles
The proton exchange membranes (PEMs) in a hydrogen fuel cell experiences hundreds if not thousands of cycles between wet and dry conditions during their service life, which leads to swelling and shrinking of the membrane material. This can lead to mechanical failure in the membrane which allows leakage or crossover of reactant gases. This mechanical fatigue is of particular importance in the catalyst layer where the polyfluorosulfonic acid ionomers, often used as an ionically conductive binder, are confined in domains on the order of tens of nanometers in thickness. A further understanding of the swelling-induced stresses experienced in both the catalyst layer as well as the PEM is necessary. In this work, we use a measurement platform based on cantilever bending to investigate the swelling-induced stresses and associated mechanical properties of Nafion thin films exposed to cyclic humidity conditions. Additionally, the influence of thermal annealing was investigated. The mechanical properties and swelling stresses were found to be strongly influenced by both the polymer film thickness and thermal annealing. It was found that thermal annealing leads to the formation of sulfonic anhydride crosslinking between the side chains of the polymer measured by infrared spectroscopy. This crosslinking leads to an enhancement in the modulus upon annealing. Furthermore, an enhancement in the modulus with decreasing film thickness was also observed that consistent with our chemo-mechanical model described in a previous publication.
, Page, K.
, Graybill, J.
, Walker, M.
, Stafford, G.
and Soles, C.
Mechanical response of thermally annealed Nafion thin films, ACS Applied Materials and Interfaces
(Accessed November 29, 2023)