Iridium und Platin-Katalysatoren für PEM-Elektrolyseure

In PEM water electrolysis, the efficiency of hydrogen generation depends on catalysts at both electrodes. A platinum catalyst is typically used at the cathode, where molecular hydrogen is formed in the hydrogen evolution reaction (HER) recombining protons and electrons formed at the anode. At the anode, however, the oxygen evolution reaction (OER) is taking place.

The oxygen evolution reaction is an electrochemical process that splits water to produce oxygen. The formation of oxygen at the anode requires a highly active and stable catalyst. Without the catalyst, the reaction will not happen. The catalyst needs to be extremely stable, because the environment combines pure oxygen, strong acidity from protons, and electrical potential, all of which accelerate chemical reactions and material degradation. 

A precious metal catalyst must therefore deliver high catalytic activity while remaining stable over many years of operation in strongly acidic conditions and under applied voltage. Iridium has the unique ability to meet both requirements for the anode side of the electrolyzer. No other element combines this level of performance and durability under such harsh conditions. 

For example, ruthenium shows even higher catalytic activity than an ir catalyst system. However, it is not stable enough in its pure form. Its performance declines over time, which limits its use in long-life systems such as PEM electrolyzers. Therefore, while options with ruthenium do exist, they also contain iridium for stability.  

Since electrolyzers are expected to operate reliably for ten years or more, a catalyst must maintain its function over long periods. This makes iridium indispensable for PEM electrolysis. Its scarcity, however, makes working with an experienced precious metal catalyst supplier critical to ensure consistent material quality and performance. 

Iridium is extremely scarce. Only about 8 to 9 metric tons are mined each year, and most of this supply is already used in other industries. Only a limited share is currently available for PEM electrolysis, and production is largely concentrated in South Africa.

At first glance, this seems to restrict hydrogen generation. Conventional PEM electrolyzer designs have required high catalyst loading, often around 400 kg of iridium per gigawatt of capacity. Based on these figures, large-scale deployment would appear limited.

However, this perspective does not reflect how modern iridium catalyst systems have evolved. A key factor is the continuous reduction of catalyst loading through a process known as thrifting. Early improvements included the use of iridium oxide instead of pure metal. A major step forward was the development of supported iridium catalysts, where the active material is distributed on a carrier structure. This maintains high catalytic activity while reducing iridium use by more than 90 percent.

Another approach involves mixed oxide systems that combine iridium with ruthenium. Ruthenium offers high catalytic activity but lower stability, while iridium provides durability. Carefully engineered combinations can balance both properties for improved reaction efficiency.

These advances are already in use. While, PEM electrolysis systems often run with 250-400kg of iridium per gigawatt, already today options are available to operate with only 100kg of iridium per gigawatt, supported by validated durability data. Future developments aim to reduce this further toward 30 kg.

In addition, iridium is not consumed during PEM electrolysis. As a precious metal catalyst, it enables chemical reactions but remains in the system over long operating times. At the end of life, iridium compounds can be recovered through established recycling processes and reused for new electrolyzers.

For these reasons, iridium scarcity is not necessarily a bottleneck. With efficient catalyst loading, recycling, and advanced material design, the required scaling of PEM electrolysis can be supported.

The amount of iridium required for PEM electrolysis has decreased significantly in recent years. Today, common systems based on iridium black typically require between 300 and 500 kg of iridium to build one gigawatt of electrolyzer capacity. This approach remains widely used because it is mature, proven, and supported by a strong body of operating experience. At the same time, it comes with very high catalyst loading, because only the surface of the iridium catalyst contributes to catalytic activity.

Modern material designs reduce this requirement substantially. By using supported iridium catalyst systems or advanced mixed oxides, the amount can already be reduced to around 300 kg per gigawatt today. These approaches increase the active surface area and improve reaction efficiency, so that much less iridium is needed to achieve the same result.

Supported catalysts distribute iridium on a carrier material, which maximizes the number of active sites in relation to mass. Mixed oxide systems combine iridium with ruthenium, using the high catalytic activity of ruthenium while maintaining stability through iridium. Both approaches are based on improving how efficiently the precious metal catalyst is used.

Importantly, these reductions are not theoretical. Low-loading systems at this level are already available and supported by performance and durability data from PEM electrolysis applications. This makes them relevant for large-scale hydrogen generation projects today.

Looking ahead, further improvements are expected. Future catalyst designs aim to reduce iridium demand to around 150 kg per gigawatt or even less, while maintaining catalytic activity and long-term stability.

Overall, this represents iridium savings of around 90 percent compared with common iridium black systems. This progress shows that catalyst loading can be reduced dramatically without compromising performance in PEM electrolysis.

Platinum catalysts are the state-of-the-art choice for the cathode in PEM electrolysis. They are highly stable in the acidic environment of the membrane and perform well at the low temperatures typical of PEM electrolyzers. Since the cathode is where hydrogen atoms are formed and combined into hydrogen, a platinum catalyst provides the reliable activity needed for efficient operation. In all cases, selecting the right Pt catalyst depends on the specific system design. 

The best platinum catalyst depends on the design of the cell and stack. Different catalyst formulations offer different strengths. Platinum black, for example, provides very high conductivity, but it also requires higher platinum loading. This makes it a strong option when robustness and conductivity are the main priorities. 

Supported platinum catalysts offer a different balance. By distributing Pt on carbon, they improve the number of active sites in relation to mass and allow lower loading. Some formulations focus on high surface utilization, while others are optimized for improved stability. This gives developers more flexibility to match the pt catalyst to the conductivity, durability, and cost targets of the PEM electrolyzer design. 

Although platinum is less expensive than iridium, it still contributes to stack cost. For that reason, the best solution is usually not one universal platinum catalyst, but the platinum catalyst that best fits the specific design of the cell. Selecting the right material therefore requires both application knowledge and catalyst expertise. 

Reducing noble metal catalyst loading in PEM electrolysis is challenging because high catalytic activity and long-term stability must be maintained at the same time. Simply using less material is not sufficient, as performance would normally decline.

Market-ready solutions require proven stability and reliable performance over time. Advanced iridium–ruthenium catalysts are already supported by test data, including accelerated degradation studies, and are available for industrial use. Well-engineered iridium–ruthenium catalysts offer not only reduced iridium content, but also show a good processability . This gives developers more flexibility to tailor performance to specific PEM electrolyzer requirements.

The underlying principle in all these approaches is to maximize the active surface while minimizing inactive material. With modern iridium catalyst architectures, this enables significantly lower catalyst loading without compromising performance in PEM electrolysis systems.

Choosing a supplier for hydrogen electrolysis catalysts goes beyond selecting a material. It directly affects system performance, long-term durability, cost, and supply chain security. It also determines how efficiently valuable materials can be recovered and reused over time.

• A key factor is deep material expertise. A qualified supplier must understand iridium catalyst, platinum catalyst, and ruthenium catalysts in detail, including their catalytic activity, stability, and behavior under real operating conditions. This includes performance under fluctuating energy input, as well as different pressure and humidity levels in PEM electrolysis systems.

• Equally important is access to proven performance data. Reliable suppliers support their materials with results from dedicated test centers, including accelerated degradation studies and long-term operation data. This is essential to validate catalytic performance and ensure that materials meet the requirements of industrial applications.

• Another important capability is the ability to reduce catalyst loading without compromising performance. Expertise in advanced formulations and thrifting approaches has a direct impact on cost and scalability, especially for precious metal catalyst systems.

• Manufacturing capability also plays a central role. A suitable supplier must be able to deliver consistent material quality and support large-scale deployment as PEM electrolysis capacity continues to grow.

• In addition, supply chain security is critical, particularly for scarce materials such as iridium. A reliable partner must ensure stable sourcing and manage supply risks effectively.

• Recycling capabilities are equally important. The ability to recover iridium complexes and oxide structures and platinum catalysts from production scrap and end-of-life systems allows valuable materials to be reused. This reduces dependence on primary resources and supports long-term cost efficiency.

• Finally, strong application support is essential. Beyond supplying materials, an experienced partner helps optimize catalyst selection and integration into the electrolyzer design.

Overall, selecting the right supplier means choosing a partner who combines material expertise, proven performance, scalable production, and secure, circular supply chains for PEM electrolysis.

Durability and lifetime in PEM electrolysis depend strongly on the choice of catalyst materials. Electrolyzers are expected to operate for more than ten years under demanding conditions, including high electrical potential, acidic environments, high temperature, and dynamic operation linked to renewable energy sources. These conditions directly affect the key functional properties of a catalyst: catalytic activity, conductivity, and stability.

At the anode, the oxygen evolution reaction creates a highly aggressive environment. Pure oxygen, protons, and electrical potential accelerate chemical reactions and material degradation. These factors can reduce catalytic activity, disrupt conductivity, and lead to structural breakdown of the catalyst. To maintain performance over time, all three properties must be preserved simultaneously. This is why an iridium catalyst is indispensable. Iridium combines high catalytic activity with exceptional stability and maintains its functionality even under these harsh conditions.

At the cathode, the environment is less aggressive, but durability still depends on maintaining catalytic activity and conductivity in an acidic medium. A platinum catalyst provides this combination and ensures stable hydrogen generation over long operating periods.

Catalyst design also plays a major role in durability. Approaches such as supported iridium catalysts or mixed oxides that combine iridium with ruthenium can reduce catalyst loading while maintaining performance. However, these designs must be carefully engineered to ensure that stability is not compromised. Ruthenium, for example, offers high catalytic activity but lower stability, so its use requires precise control to achieve long-term durability.

In real-world operation, additional stress factors such as fluctuating power input, start-stop cycles, and load changes can accelerate degradation. These dynamic conditions place further demands on catalyst materials and make stability even more critical.

For this reason, durability is not only a question of material selection, but also of validation. Accelerated degradation testing and long-term performance data are essential to ensure that catalytic activity, conductivity, and electrode structure are maintained over time.

In summary, catalyst materials determine how well PEM electrolysis systems can sustain performance under harsh and dynamic conditions. Only materials that combine catalytic activity, conductivity, and stability can deliver the long lifetimes required for industrial hydrogen production.

Research into alternatives to iridium catalysts in hydrogen production is ongoing, and a wide range of materials are being explored. Many of these aim to reduce or replace iridium in PEM electrolysis by offering high catalytic activity for the oxygen evolution reaction.

However, while some alternative materials show promising results in laboratory environments, none have yet demonstrated the combination of catalytic activity, stability, and durability required for commercial PEM electrolysis systems. The conditions at the anode are highly demanding, with strong acidity, high electrical potential, and exposure to oxygen. Under these conditions, many materials degrade too quickly to support long-term operation.

At present, there are no commercially available iridium-free catalyst solutions that meet the performance and lifetime requirements of industrial PEM electrolysis. This applies not only to established suppliers, but also across the broader market. Current developments remain at the research and development stage, and no near-term breakthrough toward fully iridium-free systems is expected.

For this reason, an iridium catalyst remains indispensable for PEM electrolysis today. Innovation in the field is therefore focused less on replacing iridium and more on using it more efficiently. Approaches such as reducing catalyst loading, improving catalytic performance, and combining iridium with other materials, including ruthenium, have already enabled significant progress.

Looking ahead, alternative catalyst materials may become viable as research advances. For now, however, the reliable and scalable production of hydrogen through PEM electrolysis continues to depend on iridium-based systems.

Electrolyzer efficiency is often defined as how effectively electrical energy is converted into hydrogen. However, in practical applications, efficiency goes beyond a single operating point. It also includes how efficiently an electrolyzer performs over time, under real operating conditions, and across its full lifetime.

At the core of this efficiency are the electrochemical reactions. In PEM electrolysis, the iridium catalyst at the anode drives the oxygen evolution reaction, which is the main source of energy loss. High catalytic activity reduces the required voltage, which lowers energy consumption. At the cathode, the platinum catalyst enables efficient formation of hydrogen atoms and minimizes additional losses. Together, both catalysts determine the overall catalytic performance and the electrical efficiency of the system.

In real-world operation, efficiency is also influenced by the ability of the system to handle fluctuating renewable energy input. When electricity supply is low, the current density in the electrolyzer decreases. Below a certain threshold, the system must be shut down. This limit is defined by the turndown ratio. Catalysts with high catalytic activity allow operation at lower current densities, which improves the turndown ratio and increases the number of operating hours.

Lifetime is another critical factor. Over time, degradation of catalytic activity or conductivity leads to higher energy demand or reduced performance. An iridium catalyst provides the stability required to maintain efficiency over many years, while a platinum catalyst ensures reliable operation at the cathode. Longer lifetimes mean more total hydrogen production for the same system.

Taken together, instantaneous efficiency, turndown capability, and lifetime all contribute to the overall effectiveness of hydrogen generation. By improving catalytic activity, maintaining conductivity, and ensuring long-term stability, iridium and platinum catalysts directly reduce energy losses and increase usable operating time.

This has a direct impact on the levelized cost of hydrogen (LCOH). More efficient operation, longer lifetimes, and higher utilization all lower the cost per unit of hydrogen produced, making PEM electrolysis more competitive in the hydrogen economy.

Ruthenium is known for its very high catalytic activity in PEM electrolysis, especially for the oxygen evolution reaction. However, in its pure form, ruthenium lacks the stability required for long-term operation under the harsh conditions at the anode. It tends to degrade over time due to oxidation and dissolution in the acidic and oxidative environment.

Iridium-ruthenium catalysts combine the strengths of both materials. Ruthenium contributes high catalytic activity, which supports efficient reaction kinetics. Iridium, in contrast, provides exceptional stability and resistance to corrosion. By integrating iridium into the catalyst structure, the overall material becomes significantly more stable while maintaining strong catalytic performance.

This improved stability is the result of how the two elements interact at the material level. Iridium helps to stabilize the catalyst surface and reduces the rate at which ruthenium degrades. It can also influence how oxygen atoms interact with the surface, lowering the likelihood of structural breakdown during operation.

As a result, iridium-ruthenium catalysts retain their catalytic activity over much longer operating times compared to pure ruthenium. This makes them suitable for PEM electrolysis systems that are expected to run for many years under demanding conditions.

In practice, developing such catalysts requires precise control over composition and structure. Well-engineered iridium-ruthenium catalysts are designed to balance catalytic activity and stability, enabling efficient hydrogen generation while reducing the overall iridium content.