Impact of Pressure and Temperature on Hydrogen Permeation in PEM Water Electrolyzers Operated at Asymmetric Pressure Conditions

Water electrolyzers are predominantly operated at elevated pressures. This is especially favorable in the context of the subsequent utilization of the produced hydrogen e.g. due to the more efficient, electrochemical and isothermal hydrogen compression or less afford for hydrogen drying. However, higher pressures lead to higher cross-permeation of the product gases in electrolysis cells. In the present contribution, hydrogen permeation across a fumea EF-40 membrane is systematically investigated for pressure differences between 5-35 bar and for four different temperatures between 22 °C and 60 °C. The measured permeation fluxes show a quadratic dependency on the pressure difference. A permeation model combining a diffusive and convective transport can describe the experimental data quantitatively. For the investigated membrane, the diffusive as well as the proposed convective permeability coefficient and their temperature dependencies are obtained. The diffusive permeability coefficient and its temperature dependency agrees very well with published data for Nafion membranes. The slightly lower value for the EF-40 can be explained by the lower water volume fraction. The obtained convective permeability coefficient indicates a high hydraulic permeability, especially in comparison to recently reported values for Nafion membranes. However, the reported values of the hydraulic permeability show high variations of about two orders of magnitude, with strong dependence on investigated materials, that show the importance of this parameter with regard to convective hydrogen permeation. The present work discusses two potential reasons for the high obtained hydraulic permeability. The first one is related to the membrane properties. In particular, the lower equivalent weight of the fumea EF-40 membrane could cause the higher hydraulic permeability. Second the electrolysis conditions, in particular the applied small current, might increase the hydraulic permeability due to wider membrane water channels and a change to a hydrophilic membrane surface. Figure: Parameterized equation in comparison to the experimental results. Figure 1