Modeling the Metal Poisoning of PEM Water Electrolyzers
Authors: Trinke Patrick , Gottschalk Torben , Eckert Christoph , Bensmann Boris , Hanke-Rauschenbach Richard 
Published: December 2024

Proton Exchange Membrane (PEM) water electrolyzers have high requirements according to the feed water quality (ultra-pure water), since different contaminations, e.g. metal ions, have negative effects on the electrochemical performance and durability. However, due to different reasons the feed water will not be free from metal ions over the whole operation time and the contaminants can be accumulating over time. Consequently, it is important to understand the underlying processes and to describe the metal poisoning.
Metal poisoning is well known, but not fully investigated yet. However, this topic will be investigated in more detail due to the importance and according to recent conference talks and discussions like at the International Energy Agency Task 30 Electrolysis group. Already in 2013 Zhang et al. showed a clear effect of sodium ions on the performance, whether the sodium ions were fed to anode or cathode side [1]. Due to reference electrode measurements they could show that the performance loss can be assigned to the cathode. Furthermore, strong changes of the pH were measured [1]. Other metal ions also affect the performance and durability, but in different manner, Becker et al. published a comprehensive review to the impact of impurities on water electrolysis [2]. The different mechanisms for metal impurities are summarized to i) substitution of protons of the ionomer and consequently leading to a loss of the proton conductivity, ii) deposition on the cathode catalyst, which lead to a reduced active surface and increase in activation overpotentials and iii) causing negative side reaction as the Fentons reactions that lead to further chemical degradation effects [2]. However, it is not easy to describe and quantify these effects. Due to the lack of detailed knowledge and above all due to the complexity, there are only few existing modeling works on this topic, such as the work of Schalenbach et al. who modeled the sodium ion transport of poisoned Nafion membranes [3].
To improve the understanding and provision of physical, numerical descriptions we are focused in this contribution on the model-based description of metal poisoning on the electrochemical performance of PEM water electrolyzers. Therefore, we use a comprehensive, multiphysical model that include charge, energy and different mass balances. We include literature and own theories into this model framework to describe the metal poisoning effect. The model is validated by literature and experimental in-house results to evaluate which effects and mechanisms are important. This will lead to a better understanding and description of the effect of metal poisoning.

References

[1] L. Zhang, X. Jie, Z.-G. Shao, X. Wang and B. Yi, Journal of Power Sources,
241, 341–348 (2013).
[2] H. Becker, J. Murawski, D. V. Shinde, I. E. L. Stephens, G. Hinds and G. Smith, Sustainable Energy Fuels,
7(7), 1565–1603 (2023).
[3] M. Schalenbach, L. Keller, B. Janotta, A. Bauer, H. Tempel, H. Kungl, M. Bonnet and R.-A. Eichel, J. Electrochem.
Soc.,
169(9), 94510 (2022).

Acknowledgments

The authors gratefully acknowledge funding by the German Federal Ministry of Education and Research (BMBF) in the framework of the projects HythroughGen (FKZ: 03HY108C) and H2Wind (FKZ: 03HY301H).