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AEM versus PEM electrolysers for hydrogen production

Electrolysers are systems that use electricity to split water molecules into hydrogen and oxygen gases, providing a means of producing emission-free hydrogen fuel.  As the world shifts towards decarbonisation and renewable energy sources, electrolysers are playing an increasingly important role in applications ranging from energy storage to sustainable aviation fuel to major industrial processes such as chemical refinement.


This article will explore the key differences between two prominent electrolyser technologies: anion exchange membrane (AEM) and proton exchange membrane (PEM) electrolysers.


Key differences between AEM and PEM electrolysers

AEM and PEM electrolysers utilise different membrane technologies to facilitate the water-splitting reaction. PEM electrolysers employ a solid polymer electrolyte that selectively conducts protons, while AEM electrolysers use an anion exchange membrane that selectively transports hydroxide ions.


PEM is a more established and commercially mature technology, but AEM electrolysers have gained significant traction in recent years due to their lower capital and operating costs. While PEM may currently offer higher energy conversion efficiency, AEM systems are catching up and can be more cost-effective, particularly for applications with less stringent hydrogen purity requirements.


Electrolysers are a crucial component in determining the levelised cost of hydrogen production. Traditionally made with expensive materials such as precious metal catalysts and complex bipolar plates, reducing electrolyser costs is vital for making green hydrogen more economically viable across sectors.


AEM electrolysers: pros and cons

💡 Anion exchange membrane: AEM technology employs a specialized anion exchange membrane that selectively conducts hydroxide ions to facilitate water splitting

First, the positive —

Anion exchange membrane electrolysers offer several advantages, including lower capital costs, reduced sensitivity to impurities in the water supply, and potentially better membrane durability compared to PEM systems. AEM technology also allows for compact, scalable devices which can be stacked to any flow rate needed.


As for cons… 

Today, AEM electrolysers are generally understood to have a lower energy conversion efficiency and slower response times to fluctuating power input when compared to PEM. AEM electrolysers may also at times produce hydrogen with lower purity levels compared to PEM systems.

However! With the latest in tech advancements, AEM systems are getting closer and closer to matching PEM in terms of energy efficiency and response times to fluctuating power input. And despite any lingering tradeoffs, they also offer rapid startup and shutdown capabilities as well as efficient load-following, making them suitable for decentralized hydrogen production and renewable energy storage systems. 

Ultimately, AEM technology offers a response capacity similar to PEM at a cheaper cost (one reason being that nickel can be used instead of the expensive titanium coating required of PEM), and with less rare Earth metal requirement.


PEM electrolysers: pros and cons

💡 Proton exchange membrane: PEM electrolyzers utilize a solid polymer electrolyte membrane that selectively conducts protons during electrolysis

The positive… 

Proton exchange membrane electrolysers are known for their high energy conversion efficiency, rapid response to fluctuating power input from renewable sources (ideal for grid-balancing), and ability to produce high-purity hydrogen suitable for applications like fuel cell vehicles and electronics.

PEM systems can also generate hydrogen at high pressures, which reduces the need for additional compression equipment and can lower overall system costs. They’re also lighter and more compact, making them viable for on-site, mobile, and hydrogen refueling applications.


And the cons —

PEM electrolysers are quite expensive due to their use of precious group metal (PGM) catalysts and complex bipolar plates that require a pricy titanium coating. The solid polymer electrolyte is prone to degradation over time. PEM systems are also sensitive to impurities in the water supply, meaning an additional cost investment is required to insure proper water filtration systems are in place.


Where is the potential for bringing costs down further?

Continued innovation is crucial for reducing the costs of both AEM and PEM electrolysers. Key areas of focus might include improving energy consumption per unit of production, extending stack lifetimes, increasing stack sizes for economies of scale, stack design generally, expanding load ranges, reducing startup times, minimizing the need for scarce materials, and achieving larger scales of production.


Innovations like anion exchange membranes with improved conductivity, stability, and durability, advanced catalysts, and optimized cell designs could further enhance the performance and cost-effectiveness of AEM electrolysers. For PEM systems, developments in membrane materials, reducing membrane thickness, catalyst layers, and manufacturing processes could contribute to cost reductions.


Takeaways

The choice between an AEM or PEM electrolyser will largely depend on the specific requirements of the project at hand. Today, PEM systems make sense for applications with stringent hydrogen purity requirements or integration with intermittent renewable energy sources. Keep in mind that AEM meets the requirements of these applications as well — the tech is just less mature, and hasn’t quite caught up to PEM in terms of efficiency. AEM electrolysers are currently preferred for applications with less stringent purity needs or where durability, low costs, and rapid load-following are the main priorities. 


There will be no one-size-fits-all solution, as project requirements vary. Continued parallel development of both AEM and PEM technologies is crucial to provide project developers with a range of systems to choose from based on their unique needs and constraints. 



However — we believe that tech maturity, market volume, and increasing lifetime and efficiency improvement will give AEM electrolysers the clear front runner position, especially considering that no rare Earth materials are needed to meet the scale up potential. AEM technology will play a key role in making green hydrogen production more cost-effective, scalable, and accessible across sectors.

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