Electrolysis: Freudenberg Sealing Technologies (FST) offers customers sealing solutions for the three leading technologies.
When succinctly expressed in three sentences, the sustainable energy system of the future actually sounds quite simple. Using green electricity, electrolyzers break water down into hydrogen and oxygen. The energy stored in the hydrogen is later converted back into electric energy in fuel cells. The resulting electric current ultimately powers vehicles, heating systems for buildings, steel mills or chemical plants.
In practice, the foundation of the whole proposition, that is, producing green hydrogen using water electrolysis, is still in its infancy. But it is growing. “I firmly believe in green hydrogen as an industrial sector of the future,” said Artur Mähne, Global Segment Manager Hydrogen Technologies. He assigns an important role to FST as a development partner to electrolyzer manufacturers. The reason: Much like fuel cells, electrolyzers need hundreds of seals in cells and stacks. FST has the material, manufacturing and process know-how to develop seals for specific applications and produce them in small or large volumes.
AEL, PEM or AEM?
Today, different electrolysis technologies are becoming established in parallel. “At FST, we are mainly putting our focus on the PEM and AEM technologies. Here we have a deep understanding of the applications, are well-positioned on the material side, and have very good market access. As for the third process that is relevant to us, alkaline electrolysis (AEL), we are busy investigating the chemical resistance of the sealing material to the alkaline solution used as an electrolyte,” he said. The various processes each have different strengths and are suited for different uses (see below). “We assume that we will find all three technologies relevant to us over the next few decades,” Mähne said.
Artur Mähne is Global Segment Manager Hydrogen Technologies at Freudenberg Sealing Technologies.
The highest state-of-the-art is to provide the customer with seals as so-called two-component applications, not as separate seals. That means, for example, that FST integrates the seal directly into a bipolar plate or in a thermoplastic or metallic frame that encloses the plate. Two-component integration offers customers added value. Among other things, it facilitates assembly and creates a high level of process security while preventing leaks.
To accomplish all this, the seal can either be sprayed directly onto the carrier – the technical term is overmolding – or the seal and carrier are mechanically integrated with one another. “We have considerable expertise in these bonding processes, that is, the stable bonding of elastomers with metal or plastic. For electrolyzers, we are currently pursuing various ingenious approaches,” Mähne said.
Many Paths to the Goal
When it comes to the green methods of water electrolysis, three out of four different processes are turning out to be promising for Freudenberg Sealing Technologies (FST). They have advantages and disadvantages:
AEL Electrolysis (Alkaline Electrolysis)
Alkaline electrolyzers are already in use worldwide on an industrial scale and have undergone the most extensive testing. They function with comparatively low-cost materials and stand out for their long-term stability. They are the technology of choice for large, stationary hydrogen-production systems with constant power supplies.
The efficiency of AEL electrolyzers is limited. They also have to be operated continually. This makes them less suited for energy sources such as solar and wind systems that fluctuate with the natural conditions. As their electrolyte, AEL electrolyzers use sodium hydroxide or a challenging corrosive alkaline solution, potassium hydroxide. AEL electrolyzers operate with limited pressure. That means the hydrogen that they produce must be highly compressed for storage and transport. These electrolyzers are ultimately very heavy and require a great deal of space. This tends to limit them to industrial applications.
PEM Electrolysis (Proton Exchange Membrane Electrolysis)
In PEM electrolyzers, a gas-tight “proton exchange membrane,” or PEM, is used instead of a liquid electrolyte. These compact electrolyzers score points for their efficiency and high performance. They also adapt quickly and flexibly to relatively large load fluctuations, such as those associated with renewable energy sources.
The process requires the use of costly precious metals such as platinum and iridium at the electrodes. PEM electrolysis is comparatively new and thus has the potential for further technical development. Improvements are needed to promote its longevity and resistance to contaminants.
AEM Electrolysis (Anion Exchange Membrane Electrolysis)
The “anion exchange membrane” (AEM) process combines the cost advantages of alkaline electrolysis with the efficiency and flexibility of PEM electrolysis. Since separation takes place under slightly alkaline conditions, inexpensive, precious metal-free catalyzers can be used for the electrodes. These small modular systems can be flexibly adjusted to meet growing demand. The German-Italian company Enapter, a close collaborator with FST on the development of forward-looking solutions, is a pioneer in this technology.
AEM’s level of technological development is comparatively low, and there is room for improvement in the service life of its membrane. AEM electrolyzers are best suited for consumer and commercial applications, and less so for the high demands of an industrial company. Small- and medium-size businesses, however, are a potential market for them.
