New Online ICP-MS Measurement Method for Studying Active Catalyst Dissolution in a Single-Cell PEM Water Electrolysis Setup
Authors: Gottschalk Torben , Moß Christopher , Trinke Patrick , Bensmann Boris , Hanke-Rauschenbach Richard 
Published: December 2024

Proton exchange membrane water electrolysis (PEMWE) faces a fundamental challenge in reducing the use of expensive and rare catalysts such as iridium and platinum. The necessary scale-up of the technology will not be possible with current catalyst loadings [1]. In recent years, the community has focused on investigating catalyst degradation and its underlying mechanisms. Kasian et al. [2] identified the significance of the electrochemical dissolution of iridium catalyst and proposed potential pathways for the dissolution. Geiger et al. [3] developed a metric known as the stability number (S-number) to compare various catalysts. The S-number correlates the amount of produced oxygen with the quantity of dissolved catalyst. Inductive coupled plasma mass spectroscopy (ICP-MS) is widely used in catalyst research to measure dissolved metals [4]. One common method for investigating catalyst dissolution in an aqueous model system is the direct connection of the ICP-MS to a flow cell [5]. Nevertheless, Knöppel et al. [6] found a difference of several orders of magnitude in S-number between aqueous model systems and single-cell PEMWE setups. Therefore, the authors conducted experiments using a flow cell setup and a special single-cell setup from which they collected water samples at the cell outlet over time. They concluded that results from aqueous systems should be cautiously treated due to the specific conditions in a flow cell that could accelerate catalyst degradation. The authors also suggest that more focus should be placed on investigating catalyst degradation in real-cell setups.

Our approach allows for a close to real-time measurement of catalyst concentrations, collected in sample flows directly from the interface of the bipolar plate and the porous transport layer or at the exit on both electrodes of a PEMWE full cell assembly. The method is capable of measuring the concentration of catalyst in the usual parts per trillion (ppt) range of a standard ICP-MS measurement. This makes it possible to investigate catalyst degradation in a PEMWE single-cell with high voltage and current resolution under different operating points. For example, the presence of iridium and platinum can be detected in the process water during the initial seconds of cell operation at conditioning. Another instance of elevated platinum and iridium concentration is observed during the transition from cell operation to an open circuit voltage (OCV) state. Figure 1 shows the amount of Iridium in the process water when switching from 3 A/cm² to OCV. This change in operating condition resulted in a distinct peak of iridium, indicating degradation. Detecting system contaminations and their influences on the single-cell setup could be another potential application in addition to investigating catalyst dissolution.

In our talk, we present the detailed operation and the setup of our new measurement method and influences of different cell operations on the catalyst dissolution in a PEMWE cell.

The authors gratefully acknowledge funding by BMBF in the framework of project H2Wind, FKZ 03HY301H.

References

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[2] O. Kasian, J.-P. Grote, S. Geiger, S. Cherevko, and K. J. J. Mayrhofer, “The Common Intermediates of Oxygen Evolution and Dissolution Reactions during Water Electrolysis on Iridium,” Angewandte Chemie (International ed. in English), vol. 57, no. 9, pp. 2488–2491, 2018, doi: 10.1002/anie.201709652.

[3] S. Geiger et al., “The stability number as a metric for electrocatalyst stability benchmarking,” Nat Catal, vol. 1, no. 7, pp. 508–515, 2018, doi: 10.1038/s41929-018-0085-6.

[4] A. Lim, M. F. Tesch, and I. Spanos, “The power of operando analysis: Understanding the critical characteristics of OER catalysts from atomistic to systemic scales,” Current Opinion in Electrochemistry, vol. 39, p. 101272, 2023, doi: 10.1016/j.coelec.2023.101272.

[5] O. Kasian, S. Geiger, K. J. J. Mayrhofer, and S. Cherevko, “Electrochemical On-line ICP-MS in Electrocatalysis Research,” Chemical record (New York, N.Y.), vol. 19, no. 10, pp. 2130–2142, 2019, doi: 10.1002/tcr.201800162.

[6] J. Knöppel et al., “On the limitations in assessing stability of oxygen evolution catalysts using aqueous model electrochemical cells,” Nature communications, vol. 12, no. 1, p. 2231, 2021, doi: 10.1038/s41467-021-22296-9.

Figure 1