The Impact of Hydrogen Crossover and Start-Stop Operation on Low Temperature Proton Exchange Membrane Water Electrolysis Degradation and Lifetime

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Hydrogen has unique advantages as an energy carrier, due to its high energy density, its ability in long term storage, and its ability to convert between electricity and chemical bonds. Although hydrogen currently has a role in transportation and agriculture, its use in energy consumption overall has been limited. With decreasing electricity prices, electrolysis cost reductions can be achieved and allow for greater use.(1) While advanced manufacturing can reduce operational cost, further capital cost reductions can be achieved by reducing the platinum group metal (PGM) content of traditionally over-engineered systems.(2-4) Efforts are underway to improve an understanding of electrolyzer degradation when accounting for load fluctuation, anode reduction during an off state, and the possible increase in mobility when operation resumes. Historical cell studies on start-stop operation have largely focused on the use of potentiostats or power supplies to set on-off operational boundaries, finding increased iridium reduction, agglomeration, and migration, significantly increasing voltage decay rates.(5-6) This effort has expanded to power supplies with smaller leak currents and relay switches to remove potentiostat/power supply contributions to cell depolarization. When relying on hydrogen crossover to reduce the anode, voltage decay rates and mechanisms consistent with constant operation have been found and include the formation of an iridium band within the membrane, iridium oxidation, and a relatively small degree of iridium agglomeration; platinum migration from the anode transport layer coating has further been found within the anode catalyst layer and the iridium band. These degradation processes, however, have generally been consistent regardless of the backpressure and amount of hydrogen at the anode, cycling count or frequency, and the length of an off state. Ex situ characterization has been leveraged to probe reasons for these observations and to explain differences between poteniostat, power supply, and fully disconnected cell stops. These types of studies are critical to understanding cost-efficiency-lifetime tradeoffs, to lead to the increased deployment of proton exchange membrane, low temperature electrolyzers. [1] B. Pivovar, N. Rustagi and S. Satyapal, The Electrochemical Society Interface, 27, 47 (2018). [2] K. Ayers, N. Danilovic, R. Ouimet, M. Carmo, B. Pivovar and M. Bornstein, Annual Review of Chemical and Biomolecular Engineering, 10, 219 (2019). [3] Cortney Mittelsteadt, Esben Sorensen, and Qingying Jia, Ir Strangelove, or How to Learn to Stop Worrying and Love the PEM Water Electrolysis Energy Fuels 37, 12558 (2023). [4] Mark Clapp, Christopher M. Zalitis, Margery Ryan, Perspectives on current and future iridium demand and iridium oxide catalysts for PEM water electrolysis, Catalysis Today 420, 114140 (2023). [5] A. Weiß, A. Siebel, M. Bernt, T.-H. Shen, V. Tileli, and H. Gasteiger, J. Electrochem. Soc., 166, F487 (2019). [6] S. M. Alia, K. S. Reeves, D. A. Cullen, H. Yu, A. J. Kropf, N. Kariuki, J. H. Park and D. J. Myers, Journal of The Electrochemical Society , 171, 044503 (2024). Figure 1

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