Your guide to electrolyzers for hydrogen production

As the energy carrier of the future, hydrogen plays an important role in the fight against global warming. To get your own reliable supply of gas, all you need are the right hydrogen production technologies. First and foremost, that means a so-called “electrolyzer.” That is the name of the device in which water is split into hydrogen and oxygen. 

You can then store that hydrogen in pressure vessels at high pressure. On demand, using a device called a fuel cell, can then produce clean energy.

The problem is that hydrogen is the smallest known molecule, which means it would take up too much space to store. That is why it must first be compressed. 

“Green hydrogen production” is splitting water molecules to create hydrogen and pure oxygen. This requires an electrolyzer, which is usually the most expensive part of such an installation in terms of capital and operating expenditures. It accounts for about 70% of the total costs of these types of hydrogen production technologies. 

But not every electrolyzer is the same. In fact, there are four main technologies. If you want to produce your own hydrogen, you first have to determine which type of electrolyzer is the optimal solution for your operation. 

That all depends on your application. Energy won from hydrogen can be used in many different areas – from hydrogen-powered buses to power plants. 
 

Let’s look at the four different electrolyzer types and what distinguishes them: 

• Alkaline electrolyzer: These are the oldest industrial electrolyzers and have been around for many years. Here, hydroxide ions are transported through the electrolyte (an alkaline solution in this case) from a cathode to an anode. This produces hydrogen. 
• Polymer electrolyte membrane (PEM): In these electrolyzers, a solid polymer electrolyte is used to conduct protons from the anode to the cathode. At the same time, the electrodes are insulated electrically. 
• Solid oxide electrolyzer: These electrolyzers use a solid ceramic material as their electrolyte and generate hydrogen in a different manner. Using elevated temperatures, the electrolyte conducts negatively charged oxygen ions. 
• Anion-exchange membrane (AEM): This emerging technology works similarly to alkaline electrolysis. However, as opposed to PEM electrolysis, it does not require the use of expensive precious metals. 

Each electrolyzer system has its own benefits and drawbacks.
 

• Alkaline: This type of electrolyzer does not require rare metals. It is much less expensive than PEM. On the other hand, it reacts slowly to fluctuation and takes approx. 20 minutes to start up. 
• PEM: This has become a very popular technology. It is more expensive than alkaline electrolyzers -- in part because rare metals are needed. However, it is quick to respond to fluctuations and starts up immediately. 
• Solid oxide: This is the most efficient technology and close to industrialization. However, for now, it is also very expensive. It stands to reason that its costs will be reduced over time once the technology is used more widely.  
• AEM: This technology, which is a combination of alkaline and PEM, has not yet been industrialized. It is flexible and doesn't require the use of rare metals. Once this technology is developed further, it could become a sustainable alternative to PEM

Each of these hydrogen production technologies has its own “sweet spot.” That determines for which applications it can optimally be used (the figures below assume a discharge pressure from 5-100 bar). 
 

• Alkaline: Here, the delivery pressure is relatively low, ranging from 0 to 16 bar and, in rare cases, slightly above that. This well-established technology is ideal for applications from 10-20 MW. 
• PEM: The normal inlet delivery pressure for this technology is 30 bar but can also be 10 bar higher or lower. Its fast response time makes it a great choice for smaller plants. Though it is more expensive, it is also suited for a wider range of applications (from 10-40 MW). 
• Solid Oxide: This technology requires steam, which means it is a great choice for any operation that generates process steam. The inlet delivery pressure is about that of the atmospheric pressure. This technology, which is still fairly new, is best for applications from 5-20 MW.  
• AEM: In terms of its applications, it is similar to PEM. The inlet delivery pressure is usually 30 bar but can be 10 bar lower or higher. This technology, which is still being refined, is ideally suited for applications from 10-40 MW. 

Atlas Copco has developed multiple technologies in-house to complement any type of electrolyzer technology. This also includes a hybrid solution that works with different types of electrolyzers and applications. 

If this sounds like the kind of flexibility that would be beneficial to you – or if you are unsure which technology is best for you – then reach out to one of our hydrogen generation specialists now. They will work with you to find the optimal solution.