For years, a single, almost invisible coating has been one of the biggest obstacles preventing green hydrogen from moving from political ambition to industrial reality. Now, a new material shows how this bottleneck can be eased — without relying on iridium, one of the world’s rarest and most expensive metals.
Green hydrogen has repeatedly been identified as a key element in the climate targets for 2030 and 2050 – but only if the technology can withstand operation at scale. Hydrogen is expected to take over part of the role currently played by coal, oil and gas in sectors such as shipping and steel production, but without releasing the greenhouse gas CO₂ into the atmosphere.
For that to happen, hydrogen must be produced directly from water and electricity on a large scale – in large industrial systems where power from wind and solar drives the splitting of water into hydrogen and oxygen — in machines known as electrolysers.
On paper, it sounds simple. In practice, the technology is not yet robust enough to deliver the quantities of green hydrogen demanded by the climate targets.
A research group from the Department of Chemistry, University of Helsinki, Finland, has taken aim at this bottleneck. In a new study, the team, led by Professor of Inorganic Materials Chemistry Pedro H. C. Camargo, has developed a new type of electrode coating for electrolysis plants that is both more active and more durable than today’s commercial reference catalysts based on ruthenium oxide (RuO₂) and iridium oxide (IrO₂), which were used as direct benchmarks under identical experimental conditions.
Inside the machines that split water into hydrogen and oxygen, much depends on a handful of thin coatings on the electrodes. These act as working surfaces where water molecules attach, are pulled apart, and sent on as hydrogen and oxygen.
“In many electrolyser designs, the oxygen-evolving anode catalyst layer is one of the most demanding components. It operates under harsh electrochemical conditions and can strongly influence both efficiency and durability, so improving it is a direct way to lower cost and increase reliability,” says Pedro H. C. Camargo.
Climate targets are pushing researchers away from rare metals
The most effective oxygen-forming coatings in use today are often based on iridium – one of the rarest metals on the planet, mined in only a few countries and in quantities that fall far short of what would be required if green hydrogen were to be scaled up globally.
At the same time, researchers have long been aware of a paradox: ruthenium oxide can be even more active, but it also dissolves more quickly. The question the team set out to answer was whether it might be possible to harness the high activity of ruthenium without inheriting all of its weaknesses.
The researchers therefore built on a material composed of the metal ruthenium bound to oxygen: ruthenium oxide. On its own, it is highly effective at helping water release its oxygen, but, as Camargo explains, it does not tolerate the harsh conditions inside the system during operation particularly well.
In laboratory tests designed to replicate operating conditions, Camargo and his colleagues introduced three more common metals – manganese, cobalt and nickel – into and around the ruthenium oxide, carefully controlling how the different components were distributed in tiny structures.
The aim was for these additional metals to support the ruthenium so that it remained just as active while becoming more resistant to wear and degradation in practice. Camargo describes the approach as an attempt to prepare an already highly active material for everyday use in more realistic electrolysis systems, rather than allowing it to shine only under ideal laboratory conditions.
“In many electrolysis plants, the oxygen-generating coating on the anode is one of the most demanding components. It operates under extremely harsh chemical and electrical conditions and plays a major role in both efficiency and service life. Improving it does not just change the price of a single component – it determines whether electrolyser systems can run stably enough to serve as the backbone of an energy system based on solar and wind power,” Camargo explains.
Where water splitting breaks down
The most challenging step in splitting water is the moment when the water molecules must release their oxygen – and this is precisely where the systems typically lose both efficiency and service life.
First, the water is broken down into more stable intermediate forms, but for a genuine oxygen molecule to be released, oxygen atoms must be brought together in pairs on the surface of the electrode. This is the slow half of the reaction and the one that consumes the most energy.
Scientists refer to this step as oxygen evolution – the point at which oxygen is fully released from the water and leaves the electrode as an oxygen molecule. It is therefore not the entire water-splitting process, but this specific oxygen step – governed by the thin, oxygen-forming coating on the anode – that the researchers set out to improve with the new material.
Ruthenium oxide is already among the most effective materials for helping oxygen escape in this reaction. It can be thought of as a particularly efficient scaffold, where the building blocks of water can settle, rearrange and ultimately be released as oxygen.
An ideal catalyst — that doesn’t last
The problem is that this scaffold does not last long enough in the chemical reality inside an electrolysis cell. Under high voltages and in highly acidic or alkaline liquids, the ruthenium slowly begins to dissolve.
Rather than simply adding another material and hoping for the best, the group chose a more controlled strategy. Starting from ruthenium oxide, they introduced small amounts of three other metals – manganese, cobalt and nickel – positioned around the active sites. Together, these additions alter how the material conducts electricity, where small defects and distortions appear in the crystal lattice, and how temporary oxygen-containing intermediates from the water attach to and detach from the surface.
The underlying idea is that these oxygen intermediates must neither bind too strongly nor too weakly. They need to remain attached long enough for the reaction to proceed, but then be released again before the surface becomes blocked.
If they bind too tightly, the process stalls. If they bind too loosely, the reaction never properly gets going. With the new mixture – a multi-metal-doped material – the researchers aim to achieve a more suitable grip on the oxygen, allowing this crucial step of water splitting to proceed more smoothly, without the coating itself breaking down as quickly as before.
The decisive factor is where the materials meet
The material itself was produced as a fine powder. First, metal compounds were deposited onto small carbon particles, which acted as a temporary scaffold. The mixture was then heated in air so that the carbon burned away. What remained was a powder of metal oxides, which was washed in acid. This step removed the most unstable components and left behind the stronger and more active surfaces.
Instead of forming a single, uniform crystal, the process produced a material made up of several distinct regions: a lattice of ruthenium oxide, slightly distorted by the added metals; small clusters of manganese oxide; and zones in which cobalt and nickel had organised themselves into a more stable crystal structure.
The results suggest an important role for the transitions between these regions – the interfaces where different materials meet and where electrons and reaction products can more readily change direction. At these interfaces, two types of metal oxides – metals bound to oxygen – ome into contact, and the electrical charge within the material is redistributed slightly.
This, in turn, affects how strongly the temporary reaction products from the water bind to the surface – and whether they are released again at the right moment. In the new material, the researchers were able to strike a better balance.
“We wanted to move away from random mixtures and towards something designed to exploit the interfaces between the phases. The work suggests that the actual contact between different oxide phases may be just as important as the average chemical composition – a view that is gaining ground in materials research, where functional interfaces are increasingly designed rather than uniform materials,” Camargo notes.
The material’s weakness became its strength
To test whether the new mixture actually made a difference, the team measured how much extra voltage was required to drive a given current through the electrode while oxygen was being formed.
This extra voltage is known as the overpotential – the additional “hill” the electrons must climb before oxygen can be produced. It is a standard metric in electrolysis research, used to compare how efficiently different catalysts drive the oxygen evolution reaction under the same conditions.
By this measure, the new material outperformed both commercial RuO₂ and IrO₂ reference catalysts under the same test conditions. Less extra voltage was needed to reach a standard current, and when the researchers increased the current, the voltage rose more slowly than is usually observed.
The effect can be compared to a bike ride. On a route filled with many steep and uneven hills, you quickly run out of energy. On a road where the hills are smoothed out, you can ride faster and for longer using the same effort. The new mixture had a similar effect on the electrons and ions that must be moved through the material to form oxygen.
From promising measurements to system-level testing
The most important test, however, was carried out in a complete laboratory setup.
The researchers used the material as the oxygen-generating electrode in an alkaline membrane system – a type of electrolysis that differs from the classic acidic systems in that it can operate with fewer precious materials and is therefore regarded as particularly relevant for cheaper, large-scale production, which today often relies on iridium.
Here, the material proved that it was not just promising on graphs. Although the system was still only a laboratory test unit, it was able to deliver current densities within a range considered industrially relevant and to operate for more than 100 hours with only a slight increase in voltage over time.
“We are encouraged that the catalyst performed well both in classic laboratory measurements and in an electrolysis setup with an alkaline membrane over 100 hours. It is still a long way from commercial viability, but it is an important step towards the durability that industry needs,” Camargo says.
From laboratory promise to real-world demands
Four days of stable operation in an electrolysis system is impressive for a laboratory material – precisely because limited service life has so far been the main bottleneck holding back green hydrogen. Even so, there is still a long way to go before reaching the many thousands of hours a commercial plant must be able to run. In the experiments reported here, the system operated under relatively calm conditions, whereas real plants must cope with frequent start-stop cycles, fluctuating loads and impurities in the water.
Camargo and his colleagues are encouraged that the material can deliver power levels relevant to industry without rapidly breaking down. At the same time, they see the next step as pushing it further – closer to the operating patterns of everyday use.
Longer-term tests are therefore now being planned, using larger systems and more realistic operating conditions, combined with measurements that follow the material as it splits water. In parallel, the researchers will explore whether the same design strategy – combining several auxiliary metals and deliberately engineered interfaces – can be applied to other catalyst systems.
Why durability matters for the climate
For Camargo, the broader question is how much green hydrogen can ultimately shift the overall CO₂ balance in industry and heavy transport.
“If green hydrogen is to make a real difference to the climate, it has to move out of pilot plants and into normal operation,” he emphasises.
That is why work on the oxygen-generating coating matters so much: it is central to whether electrolysis plants can run long enough to be scaled from pilot projects to industrial deployment.
“The more robust and resource-efficient we can make these materials, the greater the chance that large plants will actually be built – and that they can deliver the CO₂ reductions we need.”
