Investigation of Water-Molecule Network in Hydrated Polymer Electrolyte Membranes by Raman Spectroscopy: Effect of Polymer Structure and Cation Impregnation

We examined Raman spectra in both perfluorinated sulfonic acid (PFSA) and hydrocarbon (HC) membranes under different RH conditions to investigate water-molecule network. Raman spectra showed variation with relative humidity among these membranes and was affected by polymer structure. The PFSA membrane showed broad peak in Raman spectra while the HC membrane showed narrow peak even in low RH condition. These observations suggest that water-molecule network is intensively established in the PFSA membrane. We also confirmed that the K-form and the Na-form membrane showed less formation of water-molecule network than the H-form, while Na-form membrane showed less water-molecule network than the K-form. These results indicated that dissociation and ionic radius of cations affected formation of water-molecule network in these membranes.