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A new type of catalyst—a material that speeds up chemical reactions—that could make the production of clean hydrogen fuel more efficient and long-lasting has been developed by a team led by City University of Hong Kong, including researchers from Hong Kong, mainland China, and Japan.

This breakthrough uses high-density single atoms of iridium (a rare metal) to greatly improve the process of splitting water into hydrogen and oxygen, which is key to renewable energy technologies like hydrogen fuel cells and large-scale energy storage.

The researchers created a highly stable and active catalyst by placing single iridium atoms on ultra-thin sheets made of cobalt and cerium compounds. Called CoCe–O–IrSA, the final product performs exceptionally well in the water-splitting process. It requires very little extra energy (just 187 mV of overpotential at 100 mA cm^-2) to drive the oxygen evolution reaction at a high rate, and it stays stable for more than 1,000 hours under demanding conditions.

"This research is important because it tackles one of the central challenges in catalysis: how to stabilize high-density single-atom catalysts under working conditions," says Professor Johnny Ho, Associate Vice President (Enterprise) and Professor of the Department of Materials Science and Engineering, who is leading the research.

"By guiding the self-reconstruction of metastable precursors, we achieve atomically dispersed iridium anchored on a well-designed CoCe matrix, maximizing metal-substrate interactions," he adds. This strategy not only enhances catalytic activity but also significantly improves the long-term durability of catalysts for oxygen evolution, a key reaction in water splitting and renewable energy technologies."

One of the biggest challenges in this field has been keeping single metal atoms from clumping together during the reaction, which makes them less effective. The team solved this problem using an innovative method that allows the iridium atoms to arrange themselves into a stable structure under normal conditions.

They tested the catalyst in a real-world setup, using it as part of a system that splits seawater into hydrogen and oxygen. It worked continuously and efficiently for more than 150 hours, showing great promise for practical applications.

The scientists uncovered how the catalyst works at the atomic level through detailed experiments and computer modeling. They found that the single iridium atoms are the key "active sites" where the reaction happens, helping electrons move more easily and boosting the overall efficiency of oxygen production—an essential step in many clean energy systems. Although it may seem far from daily life, this research directly supports the development of efficient, sustainable hydrogen production through water electrolysis, even from seawater.

"Hydrogen is a clean fuel with zero carbon emissions when used. As the world shifts away from fossil fuels, our work contributes to making large-scale green hydrogen production more practical, cost-effective, and durable, paving the way for cleaner transportation, energy storage, and industrial processes," explains Professor Ho.

The article, titled "Atomic-scale self-rearrangement of hetero-metastable phases into high-density single-atom catalysts for the oxygen evolution reaction," has been in Nature Communications .

The next step is to extend this self-reconstruction strategy to other earth-abundant metals and complex multimetallic systems to further reduce the reliance on scarce noble metals. The team aims to integrate these catalysts into full electrolyzer systems and explore their performance in real-world conditions, such as fluctuating power supplies or natural seawater environments, to push the boundaries of practical green hydrogen production.