In-Depth Profiling of Degradation Processes in a Fuel Cell: 2D Spectral-Spatial FTIR Spectra of Nafion Membranes

We present in-depth profiling by micro FTIR of cross sections for Nafion 115 membranes in membrane-electrode assemblies (MEAs) degraded during 52 or 180 h at open circuit voltage (OCV) conditions, 90 °C and 30% relative humidity. Analysis of optical images showed highly degraded zones in both MEAs. Corresponding 2D FTIR spectral-spatial maps indicated that C-H and C═O groups are generated during degradation. The highest band intensities for both groups appeared at a depth of 82 μm from the cathode in the MEA degraded for 180 h; the same bands were present but less intense at a depth of 22 μm from the cathode. Degradation at these depths is most likely associated with the location of the Pt band formed from Pt dissolution and migration into the membrane. The two degradation bands, C═O and C-H, appeared at the same depths from the cathode, 82 and 22 μm, suggesting that they are generated by a common mechanism or intermediate. This result is rationalized by a very important first reaction: Abstraction of a fluorine atom from the polymer main chain and side chain by hydrogen atoms, H^•. This step is expected to cause main chain and side chain scission and to generate R_F-CF₂^• radicals that can react with H₂O₂, H₂O, and H₂ to produce both -COOH and RCF₂H groups.