B18 beamline celebrates its 1,000th paper: how water unlocks hidden activity in iridium catalysts
Mar 20, 2026
Marking B18’s 1,000th publication in Diamond’s database, this study showcases the significant impact the beamline continues to have on cutting-edge research. Published in ACS Catalysis, the work was led by a Diamond-funded PhD student and brought together researchers from Diamond Light Source, the University of Southampton and Johnson Matthey. By combining X-ray absorption spectroscopy on B18 with electrochemical measurements, the team uncovered how hydration enhances the activity of iridium oxide catalysts used in proton exchange membrane water electrolysis (PEMWE).
- L-R: Senior Mechanical Technician Kieran Joyce, Beamline Scientist Donato Decarolis, Principal Beamline Scientist Diego Gianolio, Senior Beamline Scientist Veronica Celorrio and Senior Support Scientist Thokozile Kathyola.
Iridium-based catalysts are currently the best anode materials PEMWE, combining high activity with the stability needed to operate in acidic conditions. As this technology is expected to play a major role in large-scale green hydrogen production, understanding what makes iridium so effective is increasingly important. Since iridium is rare and expensive, optimising its efficiency and reducing the amount needed will be essential for making hydrogen technologies more sustainable.
Hydrogen production by electrolysis relies on splitting water efficiently. While hydrogen is formed at one electrode, oxygen is produced at the other in a step (known as oxygen evolution reaction, OER) that is slow and energy intensive. Iridium oxide is one of the few materials able to survive the harsh, acidic conditions inside commercial PEMWE. However, not all forms of iridium oxide perform equally well, and until now the reasons for those differences have not been fully understood.
Using B18 for advanced spectroscopic measurements alongside electrochemical testing, the team compared how different forms of iridium oxide behave under realistic operating conditions. They discovered that water-rich, amorphous forms of iridium oxide are up to ten times more active than dry, crystalline forms. Their results suggest that water inside the material helps it adapt during the reaction, effectively “switching on” highly active sites for oxygen production.
However, this improved performance comes with a trade-off. The water-rich forms were more active, but also less stable over time. In contrast, crystalline iridium oxide was more durable, but significantly less active. Understanding this balance between activity and durability is crucial for designing future catalysts that deliver high performance while using minimal amounts of iridium.
- Principal Beamline Scientist, Diego Gianolio
Understanding this balance between activity and durability is crucial for designing future catalysts that deliver high performance while using minimal amounts of iridium.
This study highlights how in-situ, time-resolved experiments at Diamond can reveal subtle changes inside a working catalyst that are almost impossible to capture with conventional methods. By showing that water boosts the catalyst’s performance, not just fuelling the reaction, the research offers valuable insight for developing smarter, more efficient materials for large-scale green hydrogen production.
Diamond Light Source is the UK's national synchrotron science facility, located at the Harwell Science and Innovation Campus in Oxfordshire.
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