Reducing the noble metal loading and increasing the specific activity of the oxygen evolution catalysts are omnipresent challenges in proton-exchange-membrane water electrolysis, which have recently been tackled by utilizing mixed oxides of noble and non-noble elements. However, proper verification of the stability of these materials is still pending. Here we introduce a metric to explore the dissolution processes of various iridium-based oxides, defined as the ratio between the amounts of evolved oxygen and dissolved iridium. The so-called stability number is independent of loading, surface area or involved active sites and provides a reasonable comparison of diverse materials with respect to stability. The case study on iridium-based perovskites shows that leaching of the non-noble elements in mixed oxides leads to the formation of highly active amorphous iridium oxide, the instability of which is explained by the generation of short-lived vacancies that favour dissolution. These insights are meant to guide further research, which should be devoted to increasing the utilization of highly durable pure crystalline iridium oxide and finding solutions to stabilize amorphous iridium oxides.
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The authors acknowledge funding by the German Federal Ministry of Education and Research (BMBF) within the Kopernikus Project P2X and a further project (Kz: 033RC1101A). S.G. acknowledges financial support from BASF. O.K. acknowledges financial support from the Alexander von Humboldt Foundation. E.P. and T.O. acknowledge financial support from the IMPRS-SurMat doctoral program. K.J.J.M. acknowledges financial support from the DFG under project number MA4819/4-1. L.F. and Z.L. acknowledge support from the Agence Nationale de la Recherche grant SOCRATE ANR-15-CE30-0009-01. Additional thanks go to K. Hengge and T. Gänsler for carrying out the TEM and SAED measurements.
The authors declare no competing interests.
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Geiger, S., Kasian, O., Ledendecker, M. et al. The stability number as a metric for electrocatalyst stability benchmarking. Nat Catal 1, 508–515 (2018). https://doi.org/10.1038/s41929-018-0085-6
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