// P2X Electrolysis

Most energy converters draw on solar radiation, wind, running water and wave energy to generate electrical power. The availability of these renewables depends on the time of day and weather. This is why electrical energy has to be stored to ensure the power furnished to consumers is independent of these variables. A chemical energy carrier such as gaseous hydrogen, which can be produced and handled easily and very efficiently, is the first choice for longer-term intermediate storage of large amounts of energy. Electrolysis is a proven, safe and efficient technology for producing hydrogen.


Dipl.-Ing. Andreas Brinner
+49 711 78 70-338
Quality of hydrogen and refuelling
Electrolysis technology

The electrochemical splitting of water entails introducing electrical energy into water via two electrodes, a cathode and an anode, to separate it into its two gaseous components, hydrogen and oxygen. The two gases are collected and cleaned separately. Only the hydrogen has to be stored and, if necessary, transported, because it can be recombined with oxygen captured from the ambient air to form water during the energy recovery process. Hydrogen can be stored in gaseous form for any length of time. It serves as a chemical raw material for many processes around the world and as an intermediate energy storage medium – for example, as fuel for hydrogen vehicles – so the safe handling and use of hydrogen has been a matter of record for decades. There are various approaches to electrolysis. One is alkaline electrolysis, or AEL for short. It uses an aqueous potassium hydroxide solution as the electrically conductive medium. Another is polymer electrolyte membrane electrolysis, or PEM-EL, which employs an electrically conductive membrane foil between the electrode layers. A third option, high-temperature electrolysis, or SOEL, utilizes a ceramic foil between the electrodes that is conductive at a high temperature. And there are other variants of these three fundamental technologies.

ZSW investigates various electrolysis technologies.

One priority is researching and developing alkaline electrolysis technology. These activities encompass everything from developing electrodes, electrolysis blocks and plants to building and operating research and demonstration plants. The power range starts at a few kilowatts for research and test systems and extends to the lower megawatt scale for demonstration plants. Our researchers develop and build unpressurized systems as well as pressurized electrolyzers to suit the application and cost specifications.

The REG department designs end-to-end hydrogen production plants including all auxiliary units, from the electrical connection to the means of delivering hydrogen produced by AEL and PEM electrolyzers to the user. Its scientists and engineers develop installation, safety and operating concepts for hydrogen plants and support partners’ efforts to put these concepts into practice.

With our in-house AEL testing facilities, ZSW can also test and measure electrodes, electrochemical coatings, electrolysis blocks and other components developed by third parties. Unpressurized and pressurized alkaline electrolysis test systems are available to this end. They can handle 1, 10 and 100 kWe of power and operate at up to 40 bar in atmospheric and pressure modes. We have also acquired, built and now operate 0.3 and 0.5 MWe demonstration plants.

AEL-Druckteststand_April 2020
AEL pressure test rig at ZSW
Electrolysis block development

ZSW develops concepts for blocks encompassing the entire process chain, from the inceptive prototype to the mass-manufactured electrolysis block. The electrolysis block is the central component of an electrolyzer plant. ZSW has been developing alkaline electrolysis block technologies since 2011. An alkaline electrolysis block consists of many cells. The distribution structures in the individual cell frames feed in a potassium hydroxide solution and discharge the resulting gases via collector channels. A membrane in each cell serves to produce hydrogen and oxygen separately. Some of the challenges to be overcome when designing a block are how to distribute the electrolyte uniformly, how to integrate the membrane and electrode package, and how to provide a reliable seal that keeps the gases apart. There are many more application-specific requirements regarding pressure, temperature, manufacturing costs, service life, and the like to be factored into the design of the block’s individual components.

Computer-aided design (CAD) tools and simulations enable us to assess and model various inceptive design options on a small scale (100 cm²). ZSW’s extensive testing environment can accommodate, operate and measure electrolysis blocks on a scale of around 100 to 6,000 cm². We can also investigate existing block technologies’ individual components – the membrane and electrode coating – under real-world conditions. Our researchers and engineers have developed three different concepts for alkaline electrolysis blocks with active areas of 100 cm², 1,500 cm² and 2,700 cm² for atmospheric and pressurized operation up to 40 bar.  

Structure of the high-pressure alkaline electrolysis block developed at ZSW
ZSW’s 20-cell electrolysis test block
Systems development

Developing systems and plants for electrolytic hydrogen production is a focus topic at REG. ZSW started amassing its extensive expertise in the design, planning, delivery, approval, certification and operation of alkaline electrolysis plants in 2012 with a project to build a P2G-electrolysis plant funded by the German Federal Ministry for Economic Affairs and Energy (BMWi; funding code 0325524). This 1-MW alkaline pressurized electrolysis plant features the block concept developed by our researchers. We have since designed and built plants for our use and partnered with specialized companies to do the same for customers with systems tailored to their requirements. These include a simple alkaline electrolyzer for indoor installation used as 1-10 kWe test system for developing blocks, a containerized, pressurized electrolysis plant with all the necessary control and safety devices, and auxiliary supply systems for outdoor installation that deliver hydrogen to a user. The systems skill-set at ZSW extends to supervising construction and commissioning external plants. Systems design also encompasses the conceptualization and design of a rack system or container to suit the application, including all the necessary external connections, access points and installation ports. A specialized manufacturer has joined forces with us to successfully build such enclosures to meet our requirements and those of customers’ superstructures.

Electrolysis test field

The great engineering challenge in electrolytic hydrogen production is to achieve high electrical efficiency while using robust yet cost-effective materials. This is why characterizing catalytically active coatings and testing innovative materials such as cell frames, seals and membranes are such important R&D tasks.

Our aim here is to examine research results and innovations under near real-world operating conditions and on various scales so we can apply these results to the technically relevant performance classes. The focus of these investigations is on performance under varying operating conditions and on service life under defined loads.

The REG department has been working intensively on the development and use of alkaline electrolysis blocks and electrolysis systems since 2011. Engaging in the joint P2G-Elektrolysis, QUAREE100, ecoPtG and other projects, its researchers and engineers set up and operated test cells to develop and test prototypes and demonstration blocks such as ZSW’s proprietary alkaline block technology with 2,700 cm² electrode area and 300 kWe.

Established in recent years, ZSW’s extensive test field enables scientists to comprehensively characterize and investigate everything from materials for alkaline electrolysis such as coatings, electrodes and membranes to entire electrolysis blocks. Various test cells with different performance classes are available to conduct a range of investigations.


  • Potentiostat for investigating individual electrodes with cathodic or anodic coatings
  • A test cell for investigating electrodes and membranes with an active cell area of 100 cm² (blocks with up to 20 cells, current density up to 1200 mA/cm², pressure up to 16 bar, temperature up to 70°C)
  • A test cell for investigating electrolysis blocks with an active cell area of up to 1,500 cm² (blocks with up to 10 cells, current density up to 400 mA/cm², atmospheric pressure, temperature up to 80°C)
  • A test cell for investigating electrolysis blocks with an active cell area of up to 6000 cm² (blocks with up to 20 cells, current density up to 830 mA/cm², pressure up to 16 bar, temperature up to 80°C)
  • Container plant for investigating electrolysis blocks with an active cell area of up to 3,000 cm² (blocks with up to 150 cells, current density up to 600 mA/cm², pressure 16 bar, temperature up to 80°C)
Test rig for investigating high-pressure alkaline electrolysis blocks