Water electrolysis is the process that uses electricity to break down water molecules into hydrogen and oxygen. But what are the main technologies for doing so? And what should you consider when choosing an electrolyzer for your project?

Water electrolysis is the process in which water is split into hydrogen and oxygen gas through the application of an electric current. This process is a promising method for producing green hydrogen, a clean and renewable fuel that can be used in a variety of applications.

There are several different technologies that can be used for water electrolysis, each with its own set of pros and cons. Let's take a closer look at four of the most common technologies: PEM (Proton Exchange Membrane), Alkaline, AEM (Anion Exchange Membrane), and SOEC (Solid Oxide Electrolysis Cell).

Each hydrogen project is different. We advise you to let the specifics of your project drive your choice of electrolysis solution. Always do a proper project assessment at project start to review your alternatives.

PEM (Proton Exchange Membrane) electrolysis is a type of water electrolysis that uses a proton exchange membrane as the electrolyte. This technology has often been used in small-scale hydrogen production systems due to its high efficiency and fast reaction rate. One of the main benefits of PEM electrolysis is that it operates at a low temperature and is relatively safe and easy to operate. However, it is now becoming more used in medium- and large-scale hydrogen production despite it's higher CAPEX costs and lower stack life-times.

Alkaline electrolysis is another type of water electrolysis that uses an alkaline solution as the electrolyte. This technology has been in use for more than a century and is commonly used in hydrogen production systems from medium- to large-scale. One of the main advantages of alkaline electrolysis is that it can operate at a relatively low cost, making it an attractive option for producing hydrogen on a small scale. However, it is generally not as flexible in power input as PEM & AEM technologies, and has a longer start-up time (especially from cold-start). There-fore, Alkaline electrolyzers have traditionally been chosen for steady-state use-cases, but new variants are being developed to address these limitations.

AEM (Anion Exchange Membrane) electrolysis is a type of water electrolysis that uses an anion exchange membrane as the electrolyte. This technology is relatively new and is not yet widely used for hydrogen production. One of the main benefits of AEM electrolysis is that it can operate at high efficiency and at a low cost. However, has yet to be scaled up to MW-scale projects.

SOEC (Solid Oxide Electrolysis Cell) electrolysis is a type of water electrolysis that uses a solid oxide electrolyte as the electrolyte. This technology is still in the development phase and is not yet widely used for hydrogen production. One of the main benefits of SOEC electrolysis is that it can operate at high efficiency and at high temperatures, which makes it well-suited for large-scale hydrogen production. It is deemed to be a promising candidate for hydrogen production where heat is abundant, such as large industrial sites and nuclear power plants. However, the SOEC technology is yet to be fully commercialized.

In summary, each of the different technologies for water electrolysis has its own set of pros and cons for green hydrogen production. PEM electrolysis is efficient and safe, but it may be more expensive for large-scale projects. Alkaline electrolysis is low-cost, but it is not yet as flexible as PEM. AEM electrolysis has the potential to be low-cost and efficient, but is not yet widely used. SOEC electrolysis has the potential to be efficient and well-suited for large-scale production, but it is still in the development phase.

Anton Frisk, CPO of Southern Lights AB
anton@southernlights.io