Electrolysis is the process of using electricity to split water into hydrogen and oxygen. It’s a foundational technology for clean hydrogen production, especially when paired with renewable electricity to produce green hydrogen. While all electrolyzers rely on this same basic process, differences in membranes, catalysts, and operating conditions can significantly impact performance, cost, and durability.
In this interview, David Bow, Chief Strategy Officer at Power to Hydrogen, discusses with AZoCleantech the features of both AEM and PEM electrolyzers and the benefits of each system.
What is the main difference between an AEM and a PEM electrolyzer?
AEM (Anion Exchange Membrane) electrolyzers transport negatively charged hydroxide ions across a membrane in an alkaline medium. PEM (Proton Exchange Membrane) electrolyzers, conversely, move positively charged protons through a solid polymer membrane in an acidic environment.
These differences influence everything from material selection to system cost and operating flexibility.
How does an AEM electrolyzer work?
In an AEM electrolyzer, water enters the cathode side of the cell stack, where the water molecules split into hydrogen and hydroxide ions. The hydroxide ions then move through the membrane to the anode side, where they form oxygen and water. The alkaline environment enables the use of non-precious-metal catalysts such as nickel (Ni), significantly reducing material costs.
What are the key benefits of AEM electrolyzers?
AEM electrolyzers offer reduced reliance on rare earth and precious metals, lowering CapEX; enabling simpler and compact balance-of-plant configurations; and delivering good efficiency at full, partial, and dynamic operating conditions, ideal for use with intermittent renewable power. Combined with providing high-purity hydrogen, these advantages make AEM systems attractive for distributed hydrogen, behind-the-meter industrial loads, and cost-sensitive deployments.
What challenges do AEM electrolyzers still face?
While AEM is a state-of-the-art technology, it has less long-term field data than PEM systems. While early generations of the technology faced durability and membrane stability issues, ongoing advancements in membrane chemistry, catalyst coatings, and stack design have rapidly improved lifetime performance and reliability.
How does a PEM electrolyzer work?
In a PEM electrolyzer, water enters the anode side of the cell stack, where the water molecules split into protons and oxygen. The membrane allows only protons to pass through to the cathode side, where hydrogen is produced.
Because the system operates under acidic conditions, PEM electrolyzers typically rely on precious-metal catalysts such as platinum (Pt) and iridium (Ir), thereby increasing CapEx.
What are the main advantages and limitations of PEM electrolysis?
PEM electrolyzers offer high hydrogen purity, compact system design, and strong performance in dynamic operating conditions. These attributes make PEM a strong fit for mobility fueling, grid services, and behind-the-meter industrial plants.
However, there are a few key challenges. One is the system's high capital costs, driven by sustained high current densities and the use of rare-earth and precious-metal catalysts. These scarce materials also entail supply chain risks. In addition, in the long term, membranes and catalysts may degrade, necessitating careful monitoring.
These limitations are especially significant in large-scale or baseload hydrogen projects.
How do AEM and PEM electrolyzers compare on efficiency and energy use?
Both technologies can achieve high efficiency, compact design, and high hydrogen purity. While AEM systems offer the highest efficiency and require less stringent water purity. PEM systems can offer stable performance with further turn-down capabilities.
Which technology is more cost-effective?
AEM offers lower CapEx due to lower-cost materials and better Opex by having a better operating efficiency with simpler system components. PEM systems have higher CapEx, particularly at large scale, due to their requirement for rare-earth and precious-metal catalysts and additional material components.
How do materials and catalysts differ between AEM and PEM systems?
PEM uses platinum-group metals to withstand acidic conditions, whereas AEM uses abundant, non-precious metals in alkaline environments. This difference has major implications for cost, scalability, and supply chain resilience.
Which technology is more mature and commercially ready?
AEM is progressing rapidly through commercialization, with increasing adoption in pilot and commercial projects with strong momentum toward larger deployments. PEM electrolysis is fully commercialized, with a select few suppliers having substantial field data and well-established supply chains.
How should developers choose between AEM and PEM?
The decision depends on many project-specific factors. These include the availability and pricing of electricity systems, which require users to consider their budget constraints. In terms of performance, the desired operating pressure, runtime, and duty cycle are key considerations, as are long-term scaling plans.
While AEM aligns well with cost-sensitive projects both in CapEX and OpEx, PEM has a longer track record and may offer an edge on bankability.
What does the future look like for AEM and PEM electrolyzers?
AEM electrolyzers are expected to gain ground as install base grows, and cost advantages become more pronounced. PEM electrolyzers are taking the lead on new installations over traditional alkaline technology and will continue to serve as reliable, proven solutions for large-scale hydrogen production.
Advances in membranes, catalysts, and hybrid designs will further differentiate use cases for each technology.
How is Power to Hydrogen advancing electrolyzer technology?
Power to Hydrogen develops hybrid AEM electrolyzers that reduce dependence on rare-earth and precious metals while prioritizing durability, efficiency, and long asset life. The company works closely with clients to evaluate project requirements, model costs, and deploy systems optimized for real-world operating conditions.
What’s the next step for teams planning a hydrogen project?
Early technical evaluation is key. By assessing operating targets, electrical infrastructure, water quality, and long-term operating goals, developers can select the electrolyzer technology that best supports their project’s success.
This information has been sourced, reviewed, and adapted from materials provided by Power to Hydrogen.
For more information on this source, please visit Power to Hydrogen.
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