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Seawater can be used to produce hydrogen by electrolysis, and laboratory studies have reported promising durability and current density. But direct seawater splitting is not yet established commercial practice: chloride reactions, corrosion and mineral deposits make sustained operation difficult. A separate route—desalinating seawater first, then using established electrolysis technologies—adds water treatment but gives the electrolyser a more controlled feed.
How does direct seawater splitting work?
An electrolyser uses electricity to split water into hydrogen and oxygen. In direct seawater electrolysis, seawater is fed to the system without conventional desalination or enhanced pretreatment. In the indirect route, seawater is first desalinated and purified, and the resulting high-purity water is electrolysed.
The direct approach aims to avoid the desalination step, but seawater is not simply pure water with salt added. Its dissolved ions create competing reactions and deposits that the system must manage. As the authors of a 2024 Nature Sustainability paper put it, “because of the complex ion environment, direct electrolytic splitting of seawater faces major challenges, notably chlorine evolution, corrosion of electrodes and other side reactions” (Fan et al., 2024).
What makes seawater difficult to electrolyse?
Chloride reactions at the anode
At the anode, chloride can compete with the reaction that produces oxygen. Chlorine and other chlorine-containing products can create safety, product-quality, corrosion and efficiency concerns. Their formation is one reason that results from an ordinary water electrolyser cannot simply be assumed to carry over to raw seawater. Reviews of direct seawater splitting describe electrode side reactions and corrosion as central obstacles (Xu et al., Chemical Communications, 2023).
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Mineral deposits at the cathode
At the cathode, water reduction can raise the local pH. That shift can encourage magnesium and calcium in seawater to form hydroxide deposits on the electrode. Deposits can cover active sites and foul the surface, reducing performance. Corrosion and other side reactions can also shorten catalyst life.
Why one design may not solve every problem
Researchers are testing different combinations of catalysts, surface layers, membranes, electrolytes and device configurations. For example, a 2024 Nature Communications study reports that its Mo2N system forms ammonium in situ; the authors propose that this helps constrain local hydroxide and reduce magnesium hydroxide precipitation in their tested system. That proposed mechanism is specific to the reported design, not a universal fix (2024 study).
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A separate 2024 study designed a layered double hydroxide catalyst with carbonate ions in its interlayers and graphene quantum dots on its surface, aiming to reduce chloride adsorption and improve resistance to chloride corrosion. These are examples of active research strategies, rather than evidence that seawater-derived side effects have been eliminated across systems (Fan et al., 2024).
What have laboratory studies demonstrated?
Fan and colleagues reported more than 2,800 hours of stable electrolysis at approximately 1.25 A cm−2 for their catalyst test. In the same paper, their photovoltaic-electrolysis device for overall seawater splitting achieved a reported solar-to-hydrogen efficiency of 18.1% and 200 hours of stability at a working current above 440 mA. These are results for the study’s catalyst and device configurations; they should not be read as commercial operating specifications or as proof of year-round plant performance (Nature Sustainability, version of record 9 February 2024).
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The figures show meaningful progress on performance and durability under reported experimental conditions. They do not by themselves establish the costs, lifetime, maintenance needs or output of a commercial facility. A different 2024 study also reports a hydrogen production rate and calculates a hydrogen cost for its Mo2N system; that calculation depends on the study’s assumptions and apparatus, so it is not a verified market price or bankable project estimate (Nature Communications, 2024).
Direct seawater splitting or desalination first?
| Consideration | Direct seawater splitting | Desalination, then electrolysis |
|---|---|---|
| Feed preparation | Aims to use seawater without conventional desalination or enhanced pretreatment; requirements depend on system design. | Adds desalination and purification before electrolysis. |
| Electrolyser environment | Chloride and other ions bring risks from side reactions, corrosion and mineral deposits. | High-purity feed supports more stable operation with established electrolysis technologies, according to the 2025 technical review. |
| Maturity in the cited review | Research and demonstration; the review says most work remained at laboratory scale. | Uses established electrolysis technologies with a water-treatment step. |
| Main scale-up question | Can performance last under realistic, sustained operation while controlling seawater-derived side effects? | How do treatment energy, water-treatment equipment, integration and total project economics affect the system? |
The comparison reflects the technical review’s account of the two routes, with direct-route challenges also discussed in the 2023 review (RWTH Aachen University technical review, 2025; Xu et al., 2023). Avoiding conventional desalination does not automatically make direct splitting cheaper: the available evidence here does not establish comparable project-level costs or lifecycle impacts for the two routes.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Is direct seawater electrolysis commercially viable now?
A 2025 technical review reports that most direct seawater electrolysis research remained at laboratory scale and that it found no operating commercial renewable-hydrogen projects based on direct seawater splitting. It also identifies a Chinese demonstration project launched in 2023. Those are the review’s status findings, not a guarantee of project status after its publication; demonstration activity should not be confused with established commercial operation (RWTH Aachen University technical review, 2025).
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For now, the strongest case for direct splitting is as a research pathway that could reduce dependence on conventional feedwater treatment if it can deliver reliable performance at scale. The alternative of desalination followed by established electrolysis involves additional treatment, but it avoids exposing the electrolyser to the full seawater ion mixture. Which route makes sense for a project depends on the treatment system, electrolyser, integration and economics; the cited studies do not establish a universal cost winner.
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