New Discovery on Iridium Dioxide Catalysis for Efficient Green Hydrogen Production

Green Hydrogen Catalysis Redefined: Study Challenges Fundamental Assumption about Water Electrolysis

2025-07-09 Source: Universität Duisburg-Essen 2 min Reading Time

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New findings on oxygen gas evolution on iridium dioxide refute a fundamental principle of catalysis research. The study by the University of Duisburg-Essen opens up new approaches for more efficient catalysts in green hydrogen production.

Oxygen is produced in a ‘Walden-like mechanism’ in which adsorption and desorption occur in a concerted manner, analogous to homogeneous variants.(Bild: UDE/ Muhammad Usama) — Oxygen is produced in a ‘Walden-like mechanism’ in which adsorption and desorption occur in a concerted manner, analogous to homogeneous variants.
(Bild: UDE/ Muhammad Usama)

There are two basic types of catalysis: homogeneous catalysts have the same physical state as the substances being converted (e.g., they all are liquid), while heterogeneous catalysts are in a different phase, for example a solid that reacts with liquids or gases. For a reaction to take place on the surface of a solid catalyst, the starting materials (reactants) must attach to its surface (adsorption) and then dissolve again after the reaction has taken place (desorption).

Until now, research into solid catalysts — i.e., the heterogeneous variant — has assumed that adsorption and desorption occur sequentially: the reactant binds to the catalyst, reacts, and then the product dissolves. In homogeneous catalysis, however, it is known that these steps take place simultaneously.

When modelling reaction mechanisms in heterogeneous catalysis, possible simultaneous elementary steps have not always been taken into account. However, a theoretical study within the Resolv Cluster of Excellence now shows that the solid iridium dioxide (IrO₂), which is used as an anode material for the production of green hydrogen, behaves similarly to a homogeneous catalyst with regard to oxygen evolution: oxygen is produced in a ‘Walden-like mechanism’ in which adsorption and desorption occur in a concerted manner, analogous to homogeneous variants. This contradicts previous ideas and opens up new possibilities for improving solid catalysts that are more closely aligned with the principles of homogeneous processes in solution.

Exner's research builds on several joint projects within the University of Duisburg Essen and the University Alliance Ruhr: the Natural Water to Hydrogen project headed by Prof. Dr Corina Andronescu, the Collaborative Research Centre 247 Heterogeneous Oxidation Catalysis in the Liquid Phase and, last but not least, the research in the new Active Sites building, for which the ground-breaking ceremony recently took place.

Image: Illustration of the Walden-like mechanism in which water (H₂O) adsorbs on the catalytically active surface and oxygen (O₂) detaches at the same time. Oxygen atoms are shown as large red spheres, hydrogen is symbolised by the smaller white ones. Iridium atoms are represented as large, light green spheres.

Original Publication: Usama, M., Razzaq, S., Hättig, C., Steinmann, S. & Exner, K. S. Oxygen evolution reaction on IrO2(110) is governed by Walden-type mechanisms. Nat. Commun. 16, 6137 (2025). https://doi.org/10.1038/s41467-025-61367-z

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