Material Expertise for Water Electrolysis

Artur Mähne is Global Segment Manager, Hydrogen Technologies, at Freudenberg Sealing Technologies. He holds worldwide responsibility for the hydrogen technologies sales field in the energy segment, with a focus on electrolyzers and fuel cells. He considers it vital to develop customer-specific sealing solutions that make the industrial production of electrolyzers possible. “We are setting a course for the future and developing a new emerging industry and new markets.” 

Alkaline Electrolysis (AEL)

Process: AEL uses an aqueous potassium hydroxide (KOH) or sodium hydroxide (NaOH) as the electrolyte to increase the conductivity of the water. Electrodes are dipped into the solution, kept physically apart from one another and then connected exclusively by electric current, which breaks down the water into oxygen and hydrogen. The hydrogen is formed at the cathode and the oxygen at the anode.

Advantages: AEL is a process that has been tried-and-tested over the years. Since no precious metals are involved, the investment is less than with other processes.

Disadvantages: Alkaline electrolyzers need plenty of space, along with a constant supply of electric current, so they are not particularly suited for operation with wind or solar power. Since the solution in their interiors is corrosive, they are subject to strict safety standards.

Proton Exchange Membrane (PEM) Electrolysis

Process: PEM electrolysis uses a solid polymer membrane as the electrolyte. The membrane separates the two electrodes, which contain catalysts in the form of precious metals. When the current flows through the electrolyzer, water is broken down into protons, electrons and oxygen at the anode. The protons migrate through the membrane along the electric field to the cathode, becoming hydrogen.

Advantages: PEM electrolyzers can be ramped up from standby operation quickly. This makes them ideal for use with renewable energy sources such as wind or solar power. The resulting hydrogen is also extremely pure. They have a compact design and can be used in relatively small systems.

Disadvantages: PEM electrolyzers are costly to make since they use precious metals such as platinum and iridium, along with titanium and fluorinated membrane polymers. The systems are also more sensitive to contaminants than alkaline electrolyzers.

Anion Exchange Membrane (AEM) Electrolysis

Process: In AEM electrolysis, hydrogen is formed at the cathode. Negatively charged hydroxide ions migrate through the anion exchange membrane (AEM) to the anode, where the oxygen is formed. The process uses a highly-dilute, alkaline solution as a liquid electrolyte, which protects the electrodes from corrosion on one hand and improves the conductivity of the water on the other.

Advantages: In its flexibility, AEM electrolysis is similar to the PEM process. It can also be used in combination with wind and hydropower systems. But it does not use precious metals, which is why AEM electrolyzers are less expensive to produce. They are theoretically an ideal compromise between AEL and PEM electrolysis.

Disadvantages: AEM electrolysis is a relatively new technology and has not been fully tried-and-tested, especially regarding the stability of its membrane materials. As a result, little empirical data is available on lifespans and longterm stability.