State of Water in Perfluorosulfonic Ionomer (Nafion 117) Proton Exchange Membranes

Abstract

The nature of water in acid-form Nafion 117 was quantified at several hydration levels by dielectric relaxation spectroscopy. Two independent experimental setups were used to collect complex dielectric permittivity spectra at low frequencies ͑0.01 Hz to 1 MHz at −80 to 25°C͒ and in the microwave region ͑0.40-26 GHz at 25-45°C͒. We directly observed the states of water, manifested through three population averages with distinctly resolved dynamical behaviors, and their changes with temperature and hydration level. The fastest process observed was identified as the cooperative picosecond relaxation of free ͑isotropic, bulklike͒ water, whereas the slowest process ͑microsecond relaxation times͒ corresponded to water molecules strongly bound to the charged sulfonic groups. A third type of water was also observed, also characterized by picosecond relaxation times, close to and about three times slower than those of bulk water, which was attributed to loosely bound water and may contain substantial dynamical heterogeneities.

Towards a NMR-Based Method for Characterizing the Degradation of Nafion XL Membranes for PEMFC

“…The chemical shift of the most intense component at 4.69 ppm corresponds approximately to that observed in non-reinforced hydrated PFSA membranes at equivalent temperature and water content: Nafion NR211 (6.20 ppm), Gore 800 (5.83 ppm at 98% RH). 22 In unreinforced Nafion, water is known to exist in different states, [23][24][25][26] namely non-freezing water, bound freezing water and free water. Although dielectric relaxation spectroscopy is able to describe different responses relative to these populations, the spectral resolution of proton NMR performed at room temperature is not high enough to detect them directly.…”

MoS2-based materials as alternative cathode catalyst for PEM electrolysis

“…The Nafion membrane was treated [19] before use by washing in 5 % H 2 O 2 for 1 h at 80 °C to eliminate residual organic impurities [20], then in 0.5 M sulphuric acid for 1 h at 80 °C to incorporate water molecules and activate the membrane by hydration [21] and finally with boiling water for 1 h. The pre-treated membranes were stored in water at ambient temperature prior to deposition of the catalyst materials.…”

Degradation aspects of water formation and transport in Proton Exchange Membrane Fuel Cell: A review

“…Each of these types has different freezing points depending on the nature of their molecular chemical bonds. For instant, Lu et al [286] detected three distinctive water states in subfreezing temperatures using a dielectric relaxation spectroscopy technique. They found in the kHz frequency region that water molecules are hydrogen-bonded to the sulfonates whereas in the GHz domain water molecules are either in liquid bulk-like or loose bond forms.…”