Analysis of Gas Permeation Phenomena in a PEM Water Electrolyzer Operated at High Pressure and High Current Density

In this study, on-line mass spectrometry is used to determine hydrogen permeation during proton exchange membrane water electrolyzer (PEM-WE) operation for a wide range of current densities (0-6 A cm-2) and operating pressures (1-30 bar, differential pressure). H2 permeation measurements with a permeation cell setup, i.e., without applying a current, show a linear correlation between permeation rate and H2 partial pressure, indicating diffusion as the main crossover mechanism. Measurements with full membrane electrode assemblies (MEAs) during PEM-WE operation reveal a significant increase of the gas permeation rate at high current densities, by up to ≈20-fold at 1 bar H2 and up to ≈1.2-fold at 30 bar H2 (Nafion® 212 or Nafion® 117 membrane; Ir-black (anode) and Pt/C (cathode)). Recently, H2 super-saturation of the ionomer phase in the cathode catalyst layer was shown to be the reason for this increase, and we discuss the impact of this effect for different electrode compositions and operating conditions. Finally, the determined H2 permeation rates and electrolyzer performance are used to discuss the overall PEM-WE efficiency for different membrane thicknesses and it is shown that the formation of an explosive gas mixture in the anode at low current densities requires additional mitigation strategies.