Understanding Gas Permeation during High Pressure Operation of PEM Water Electrolyzers

Abstract

Governments and industries across the world have initiated implementation of clean hydrogen (H2) to achieve zero emissions, yet significant challenges remain for large scale adoption. With the decreasing renewable electricity cost PEM water electrolyzers (PEMWEs) show significant potential for at scale deployment due to their high faradaic efficiency and high operating current density. To reduce the per kilogram price of hydrogen and increase the overall energy efficiency, PEMWEs need to be operated at high differential pressures (30 to 50 bar) to eliminate the need for compression during storage and transportation1. To achieve high faradaic efficiency, thinner membranes are required to reduce voltage losses within the cell. However, thinner membranes exhibit a higher gas permeation rate which leads to increased crossover of hydrogen from the cathode through the membrane to the anode. Such increased crossover of H2 not only reduces the efficiency but can also result in flammable gas mixtures (lower flammability limit for H2 in O2 is 4 %) as Iridium/Iridium oxide (anode catalyst) is inefficient in oxidizing H2 1. The addition of a gas recombination catalyst (GRC) to the membrane is an useful strategy to oxidize permeating H2 and minimize the H2:O2 ratio at the anode.In this study, a high pressure (up to 30 bar) electrolyzer setup is coupled with online gas chromatography-mass spectrometry to understand the H2 gas permeation in membranes as a function of H2 partial pressure and operating current density (simulated by varying the flow rates) as shown in Figure 1 . Effect of the GRC, its loading, and its location on the H2 permeation will be elucidated. Differences induced by the addition of anode and cathode catalyst layers on H2 permeation rates will also be presented.Figure 1. Ex-situ H2 permeation rate at different cathode operating pressure at 80 °C. The anode was maintained at 1 bar of O2 partial pressure Acknowledgement This research is supported by the U.S. Department of Energy (DOE) through the Hydrogen and Fuel Cell Technologies Office, program manager Dave Peterson Reference Bernt, M., Schröter, J., Möckl, M. & Gasteiger, H. A. Analysis of Gas Permeation Phenomena in a PEM Water Electrolyzer Operated at High Pressure and High Current Density. J. Electrochem. Soc. 167, 124502 (2020). Figure 1