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Yes, hydrogen can be made by electrolysing seawater directly, and projects have reached pilot and trial scale. But as of the evidence reported through 2025, direct seawater electrolysis has not demonstrated a clear general advantage over desalinating seawater first and using established electrolysis. Its prospects depend on proving safe, durable operation and a real benefit for particular sites—not merely showing that a pilot can run.
What “direct from seawater” means
Direct seawater electrolysis feeds seawater into an electrolyser without first desalinating it or substantially purifying it. The alternative, indirect seawater electrolysis, treats seawater first and then uses established water-electrolysis technology. The comparison is not simply free ocean water versus costly freshwater: direct systems must handle seawater’s dissolved salts and other constituents, while the indirect route requires treatment equipment, energy and brine management.
The European Commission Joint Research Centre (JRC) treats the indirect route as the benchmark because water purification and electrolysis are established technologies. Its 2025 review reported that an initial Web of Science search for “seawater electrolysis AND hydrogen production” found 748 papers published from 1992 through April 2024. That count describes the search results, not the number of successful or commercially proven systems. Read the JRC review.
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Why splitting seawater is difficult
Chloride competes with oxygen production
In an electrolyser, the anode is where oxygen is intended to form. Chloride in seawater can instead participate in competing chlorine-evolution chemistry. This can reduce useful hydrogen-production efficiency and create chlorine or related compounds that need safe containment and handling. The same chemistry can contribute to electrode corrosion and faster catalyst degradation.
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Mineral deposits and fouling undermine reliability
Under alkaline conditions, calcium- and magnesium-containing deposits can build up on electrodes and block active sites. Fouling, corrosion and degradation all increase maintenance demands and threaten long-term operation. These are coupled system problems: a catalyst that performs well in a short laboratory test does not establish that a complete electrolyser can operate safely and reliably over time.
Materials research is promising, not proof of readiness
Researchers are exploring selective catalysts, protective or chloride-repelling layers, membranes, membraneless designs and hybrid approaches. These strategies aim to limit unwanted reactions or protect components, but the JRC’s review describes direct seawater electrolysis as immature. A materials advance alone does not establish commercial viability. The JRC review and a 2025 technical review by Augustin and Wintgens discuss the technical challenges. Read the technical review.
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What the pilot projects show—and what they do not
The International Energy Agency’s Global Hydrogen Review 2025 reports two Chinese milestones in December 2024:
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- Sinopec completed a 100 kW pilot at its Qingdao refinery using chlorine-resistant electrodes.
- China National Offshore Oil Corporation began trial operations of a megawatt-scale seawater electrolyser and completed a test run.
These projects show that direct seawater electrolysis has moved beyond small laboratory experiments into larger pilot and trial settings. The reported milestones do not, by themselves, establish sustained availability, delivered hydrogen cost, lifecycle emissions or commercial operation. See the IEA’s Global Hydrogen Review 2025.
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Is direct electrolysis better than desalinating first?
That remains the central unanswered commercial question. In its review published on 20 January 2025, the JRC concluded: “There is currently no research or industrial project demonstrating clear benefits of using direct seawater electrolysis over indirect seawater electrolysis.” The same review allows that direct electrolysis could become viable for specific target applications. The conclusion is in the JRC report by Marco Serafini, Eveline Weidner and Julien Bolard.
A fair comparison must use full-system performance rather than the electrolyser alone. Relevant measures include hydrogen output and energy use; long-duration operation and component lifetime; chlorine and hypochlorite selectivity, containment and handling; pretreatment, scaling, fouling and brine management; and total cost and water availability at the proposed site. The available reports do not provide enough site-specific pilot operating and cost data to rank the routes across all these measures.
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How water and desalination figures fit into the decision
Electrolysis has a real water requirement, though its size depends on the system. Augustin and Wintgens report a stoichiometric minimum of 9 kg of water per kg of hydrogen; practical use can reach 13 kg per kg because of evaporation, leaks, losses in the oxygen stream, and cleaning or flushing.
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For context, seawater reverse osmosis accounts for 70% of globally installed desalination capacity, and its typical specific energy consumption is 3.0–5.0 kWh/m³, depending on feedwater and system design, according to the same 2025 review. These figures are not a complete energy or cost comparison between direct and indirect hydrogen production. Desalination energy alone cannot settle the question: electrolyser efficiency and durability, pretreatment, brine handling, maintenance and integration with renewable power also matter. Augustin and Wintgens provide the water and desalination context.
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Where direct seawater electrolysis could make sense
The strongest potential case is a site where freshwater is constrained and coastal renewable resources are available, particularly if avoiding or simplifying water treatment delivers a measurable system-level benefit. But the reviewed evidence does not establish a proven winning application. Any proposed project needs to show that its overall water, energy, maintenance, safety and cost profile is better for that site than desalination followed by established electrolysis.
For now, direct seawater electrolysis is a credible development pathway, not a demonstrated replacement for the indirect route. The 2024 Chinese milestones make the next questions practical ones: whether systems can run durably, manage chlorine chemistry safely, and deliver a site-specific advantage at commercial scale.
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