Impact of Iron Impurities on the Performance of PEM Water Electrolyzers
Authors: Sweeney James , Patterson Timothy , Bonville Leonard J. , Pasaogullari Ugur , Bliznakov Stoyan 
Published: September 2023

Hydrogen gas is a promising green energy solution, with enormous potential for using hydrogen fuel cells to power vehicles, homes, and for portable power applications [1]. Proton exchange membrane water electrolyzers (PEMWEs) are a viable way for the production of green hydrogen, when used in conjunction with renewable energy sources such as wind and solar. A crucial component to PEMWE is the membrane electrode assembly (MEA). MEAs are susceptible to degradation from transition metal cation impurities such as Fe 2+ [2,3,4]. The presence of iron impurities is common and can come from the feed water, cell components, and piping in the system. Concentrations of parts per million (PPM) of iron impurities have been shown to be extremely detrimental to cell performance [3, 4]. However, little work has been done to show the effects of concentrations in the parts per billion (PPB) range. Understanding the impact of Fe2+ impurities with very low concentrations in the water stream in PEMWEs on their performance is needed to assess and improve the durability of PEMWEs.
In this work, several cells assembled with MEAs with active area of 5 cm2 have been evaluated, and the impact of low-level iron impurities on their performance has been comprehensively studied. A baseline performance was established by testing a cell in pure DI water before the feedstock was replaced with stock solutions containing Fe2+ ions with various concentration in the low PPB range. The cells were tested at 50 oC, and constant current of 1.8 A/cm2 for up to 500 hrs. Diagnostic tests were taken every 25 hours, which included polarization curves and electrochemical impedance spectroscopy (EIS) measurements. Water samples were taken every day and analyzed by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), to monitor the Fe concentration in the feedstock water. In addition, water samples from the cathode were taken to investigate the fluoride emission rate (FER), to better understand membrane degradation. The findings from these experiments help to better understand the performance of PEMWEs, as well as the degradation mechanisms governing the performance loss in the MEA.

References:

[1] Carmo, M., Fritz, D. L., Mergel, J., & Stolten, D. (2013). A comprehensive review on PEM water electrolysis. International journal of hydrogen energy, 38(12), 4901-4934.
[2] Xu, S., Wang, X., Zhang, L., Sun, S., Li, G., Zhang, M., ... & Zhu, B. (2020). The Fe3+ role in decreasing the activity of Nafion-bonded IrO2 catalyst for proton exchange membrane water electrolyser. International Journal of Hydrogen Energy, 45(30), 15041-15046.
[3] Marocco, P., Sundseth, K., Aarhaug, T., Lanzini, A., Santarelli, M., Barnett, A. O., & Thomassen, M. (2021). Online measurements of fluoride ions in proton exchange membrane water electrolysis through ion chromatography. Journal of Power Sources, 483, 229179.
[4] Li, N., Araya, S. S., Cui, X., & Kær, S. K. (2020). The effects of cationic impurities on the performance of proton exchange membrane water electrolyzer. Journal of Power Sources, 473, 228617.