Carbon-neutral and sustainable hydrogen production is crucial when it comes to achieving the climate control targets. It is therefore important to identify the origin of hydrogen by name. Hydrogen is referred to as grey, blue, turquoise or green depending on its origin and CO2 emissions. As things stand today, about 90 per cent of hydrogen is still produced from fossil fuels, mostly from natural gas, and is classed as grey hydrogen. If the resulting CO2 is captured and stored underground, for example, it is then called blue hydrogen. Turquoise hydrogen is also traded as an alternative. When produced from methane, for example, it does not form CO2 but solid carbon.

Only “green” hydrogen, which is obtained by using electricity from renewable sources like wind turbines and photovoltaics, has sustainable credentials in terms of climate control. Water electrolysis is the key technology here. Not only is it the means of generating hydrogen but it also helps to balance out fluctuations in the supply of power from renewable sources, to store the renewable energy or to transfer it to other energy sectors.


Tonja Marquard-Möllenstedt
+49 711 78 70-285

// Team leader test field electrolysis (ElyLab)


Dipl.-Ing. (BA) Thomas Ottitsch
+49 711 78 70-362

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Electrolysis is an important focus in our research. Our knowledge of engineering and of the relevant systems has already been applied in the construction of various electrolysis plants all the way up to megawatt class at the ZSW, and we advise industrial customers on issues ranging from basic engineering jobs right through to the commissioning of commercial units, also maintaining some technical input in the subsequent monitoring of systems.

Electrolysis Technology

// 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.

Block Development

// 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. 

System Development

// Electrolysis System Development

Green hydrogen is an important building block in the energy transition. The eco-friendly source of energy is generated from green electricity using water electrolysis technology. There is an emphasis in the “Electrolysis Made in Baden-Württemberg” project on the roll-out of electrolysis on an industrial scale and on the guarantee of competitiveness on an international scale for small and medium-sized enterprises in Baden-Württemberg. Taking centre stage in the undertaking is an electrolysis demonstration system which was switched on by Minister of Economic Affairs Dr. Nicole Hoffmeister-Kraut on 2 August 2022. The Baden-Württemberg Ministry of Economic Affairs is backing the “BW Electrolysis” project, which is being coordinated by the ZSW, and is investing a total of five million euro.

The alkaline high-pressure electrolyser has an electrical output of around one megawatt and is built in modular fashion with the future in mind in that the basic design of this smallest unit can easily be scaled up to higher performance classes in the double-digit megawatt range. More than 40 enterprises in Baden-Württemberg have been consulted on the engineering processes required in the demonstration system in respect of capability for series production and have duly contributed components and manufacturing technologies (e.g. piping, pumps, valve systems, power electronics). The aim is to work with the enterprises on electrolysis systems in a bid to accelerate the routes to market for this technology of the future.

The “Made in Baden Württemberg” demonstration system is an alkaline high-pressure electrolysis unit (30 bar) developed by the ZSW with an electric power rating of one megawatt and a production capacity of around 20 kilogrammes of hydrogen per hour. That is enough to fill about 80 fuel cell cars, 20 fuel cell buses or fuel cell trucks every day and approximates to an annual production capacity of up to 170 tons of hydrogen.

The system is modular in design and so the technology has the scalability to be upgraded to higher performance classes and the flexibility to be adapted to different customer requirements or site conditions. The quest to roll out the system on an industrial scale was flanked in particular by work on the further development of the electrolysis stack technology, which is the heart of the system and has been patented by the ZSW, with a view to achieving a further increase in the efficiency of the electrolysis process and reducing the production costs for green hydrogen.

The ZSW has many years of experience in developing systems and equipment for the generation of hydrogen by electrolysis. Having already developed a one-megawatt alkaline pressure electrolysis system and its own block-type concept in the P2G electrolysis project funded by the Federal Ministry for Economic Affairs and Energy (Bundesministerium für Wirtschaft und Energie - BMWi), the ZSW has acquired extensive expertise in the design, implementation, approval and certification of alkaline electrolysis systems. The portfolio has since grown and we are designing electrolysis test rigs of various performance classes, all of which are equipped with the necessary control instruments, safety devices and supply systems for the delivery of hydrogen. The trials involve trying out electrolysis block components and new block designs on test rigs from around 1 to 10 kW. The system is integrated in a container on a scale of 100 - 1000 kW, making it suitable for installation in new locations as well. The ZSW has designed and built systems both for its own research purposes and for companies. One example is the flagship project “Power-to-Gas Baden-Württemberg (PtG-BW)”.  An electrolysis pilot system for hydrogen (H2) was set up in Grenzach-Wyhlen in the south of Baden.

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