Measurement system for solubility and self-diffusivity of hydrogen gas dissolved in polymer electrolyte membrane

The characteristics of hydrogen gas permeation through a polymer electrolyte membrane (PEM) are important in determining the performance of electrochemical systems such as fuel cells and electrolyzers. However, the only available data related to these characteristics are those for the hydrogen permeability, which were obtained from measurements under a given pressure difference through the PEM. Although we can derive the solubility and self-diffusivity from the permeability, the derivation requires a mathematical procedure, such as providing a gas transport model and fitting experimental data with theoretical data from the model. In this study, we developed a measurement system that uses nuclear magnetic resonance and can quantify both the solubility and self-diffusivity in a rather straightforward manner. The system allows us to measure these two properties when hydrogen gas is dissolved in a dry Nafion membrane under a hydrogen gas pressure of up to 1 MPa at room temperature. The solubility increases linearly with increasing pressure, and the solubility coefficient is (1.3 ± 0.13) × 10^-5 mol/(cm²MPa). The self-diffusivity shows a constant value of (2 ± 0.4) × 10^-6 cm²/s regardless of the pressure.