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


Dipl.-Ing. Andreas Brinner
+49 711 78 70-338

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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

Grüner Wasserstoff ist ein wichtiger Baustein für die Energiewende. Der klimafreundliche Energieträger wird mit Hilfe der Wasser-Elektrolyse aus Ökostrom erzeugt. Im Projekt „Elektrolyse Made in Baden-Württemberg“ steht die Industrialisierung der Elektrolysetechnik und die Sicherstellung der internationalen Wettbewerbsfähigkeit für mittelständische Unternehmen aus Baden-Württemberg im Vordergrund. Das Herzstück ist ein Elektrolyse-Demonstrators, der am 2. August 2022 von Wirtschaftsministerin Dr. Nicole Hoffmeister-Kraut in Betrieb genommen wurde. Das Wirtschaftsministerium Baden-Württemberg fördert das vom ZSW koordinierte Projekt „BW Elektrolyse“ mit insgesamt fünf Millionen Euro.

Der alkalische Druck-Elektrolyseur mit einer elektrischen Leistung von rund einem Megawatt wurde modular konzipiert werden, so dass die Technologie künftig aufbauend auf dieser kleinsten Einheit auf einfache Weise in größere, zweistellige Megawatt-Leistungsklassen skaliert werden kann. Über 40 Unternehmen aus Baden-Württemberg haben serientaugliche verfahrens- und elektrotechnische Komponenten (z.B. Verrohrung, Pumpen, Ventiltechnik, Leistungselektronik) und Fertigungstechnologien in den Demonstrator eingebracht. Gemeinsam mit den Unternehmen soll der Markthochlauf der Zukunftstechnologie Elektrolyse beschleunigt werden.

Bei dem Systemdemonstrator „Made in Baden Württemberg“ handelt es sich um eine vom ZSW entwickelte Alkalische Druckelektrolysetechnologie (30 bar) mit einer elektrischen Anschlussleistung von einem Megawatt und einer Produktionskapazität von etwa 20 Kilogramm Wasserstoff pro Stunde. Das reicht für die Betankung von täglich etwa 80 Brennstoffzellen-PKW, 20 Brennstoffzellen-Bussen oder Brennstoffzellen-LKW und bedeutet eine jährliche Produktionskapazität von bis zu etwa 170 Tonnen Wasserstoff.

Das System ist in einem Baukastensystem modular konzipiert, sodass die Technologie auch in größere Leistungsklassen skaliert und flexibel an unterschiedliche Kundenanforderungen oder Standortgegebenheiten angepasst werden kann.

Neben der Industrialisierung der Systemtechnik wurde insbesondere an der Weiterentwicklung der ZSW-patentierten Elektrolysestack-Technologie, dem Herzstück der Anlage, gearbeitet, um die Effizienz des Elektrolyseprozesses weiter zu erhöhen und die Herstellungskosten für grünen Wasserstoff zu senken.

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.

Electrolysis Test Field

// Electrolysis Test Field

Test rig for investigating high-pressure alkaline electrolysis blocks

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.

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