German researchers have developed new membranes designed to produce green hydrogen directly from seawater, potentially reducing reliance on purified freshwater and opening the door to coastal and offshore hydrogen production.
Direct seawater electrolysis: From ASTM purity standards to the challenges of saltwater
How pure does water need to be for hydrogen production through electrolysis? For commercial electrolyzers, whether based on proton exchange membrane (PEM), alkaline or anion exchange membrane (AEM) technology, the answer is extremely pure. More specifically, water quality must meet stringent purity requirements, including those defined by ASTM D1193 for Type I (ultrapure water) and Type II (purified or demineralized water), which establish the physical and chemical purity standards used in laboratories and advanced industrial processes.
Without sufficiently purified water, dissolved metals, minerals and salts can damage electrolyzers by poisoning catalysts, clogging flow channels or increasing electrical conductivity to the point of causing current leakage.
But as freshwater resources come under growing pressure and vast oceans remain largely untapped, researchers are turning their attention to direct seawater electrolysis. Using seawater or brackish water could expand both the range of water sources available for hydrogen production and the geographic reach of the technology, particularly through coastal and offshore facilities.
How far has direct seawater electrolysis progressed?
One of the earliest approaches to bringing electrolysis to marine environments involved integrating desalination systems directly into hydrogen production facilities. However, the additional energy requirements and complexity of integrating the two processes can make this approach expensive and difficult to deploy.
Against this backdrop, Germany launched SeaEly, a government-funded research project led by Fraunhofer IWES in collaboration with Fraunhofer IFAM, Technische Universität Berlin (TU Berlin) and several industrial partners.
The initiative, which officially concluded in March 2026, aimed to redesign the key components of an electrolysis system capable of producing hydrogen and oxygen directly from saltwater. A central objective was to determine precisely how much seawater could replace drinking water and purified process water in hydrogen production.
“The idea was to determine how pure seawater needs to be for direct use in electrolysis without placing excessive strain on the equipment,” explained Nadine Menzel, head of the electrochemistry and analytics group at the Fraunhofer IWES Hydrogen Lab Leuna.
Over the course of the project, the research team worked to scale up direct electrolysis of untreated seawater from laboratory experiments to kilowatt-scale operation, comparing its energy efficiency with established technologies, including PEM, alkaline and AEM electrolysis.
Achieving this required the development of new electrolysis membranes, which act as selective barriers, allowing certain ions to pass through while keeping the resulting gases as separate as possible.
New modular electrochemical test bench for seawater electrolysis
“At Fraunhofer IFAM, we developed new membranes for the electrolysis of untreated seawater and tested them on a modular electrochemical test bench,” said Andreas Brinkmann, a researcher in Fraunhofer IFAM’s Adhesion and Interface Research department.
Promising materials can then progress from small experimental cells to larger configurations. This approach allows researchers to assess not only the performance of individual membrane materials but also how multiple electrolysis cells interact with one another and with other system components.
However, practical performance results have not yet been published, leaving a crucial question unanswered: how much less energy-efficient is direct seawater electrolysis compared with conventional technologies, even when equipped with the newly developed membranes?
The answer will be critical in determining whether direct seawater electrolysis can move beyond experimental applications and become a viable alternative for large-scale green hydrogen production.
