Seawater electrolysis

In plain language

An electrolyser uses electricity to split water into hydrogen and oxygen. Normally the water is purified first, because dissolved salts and minerals can damage the electrodes and membranes. Seawater electrolysis tries to skip that step, so that the ocean could supply the water directly.

Seawater is chemically crowded, which makes this hard. Chloride can take part in unwanted reactions and corrode metal parts, and minerals such as magnesium and calcium can build up on surfaces and block them. Lab results so far are encouraging, but they describe particular devices and water types. It is not yet shown that a whole system, including any water treatment it needs, works better than purifying water first.

Technical explanation

At the anode, chloride ions compete with oxygen evolution and can form chlorine-containing products, which lowers hydrogen efficiency and can speed corrosion of catalyst surfaces. At the cathode, hydrogen evolution raises the local pH, so magnesium and calcium compounds can precipitate on electrode and membrane surfaces. Catalyst research tries to favour oxygen evolution and resist corrosion. Fan and colleagues report an electrocatalyst for seawater splitting at ampere-level current density, according to the title of their paper; the catalyst details were not checked against the full text. Sun and colleagues compare NiFe layered double hydroxide anodes with different anions inserted between their layers, and report a phosphate-containing version that ran for over 1,000 hours in a small test cell.

Device architecture is a separate design choice. Xie and colleagues reported a membrane-based electrolyser in Nature in 2022, in which a hydrophobic membrane separates liquid seawater from the electrolyte and lets water vapour pass through. In alkaline seawater, Sun and colleagues report a phosphate-intercalated NiFe anode running at 1.0 A per square centimetre for more than 1,000 hours in a small electrolyser, and a 1 kW-class stack reaching 0.5 A per square centimetre at about 2.0 V. These are laboratory and proof-of-concept results.

Comparing results needs care. Current density, faradaic efficiency, gas purity, electrolyte composition, electrode area, feed water and test duration all change the meaning of a result. A fair assessment of a complete system would also include electricity use, water pretreatment, chemical dosing, gas purification, compression, maintenance, component replacement and any waste streams, not only the stack or catalyst performance.

What the evidence says

Each statement is typed by the strength of its evidence and linked to the source that supports it.

Limitations and open problems

• Most reported results are at laboratory or small-device scale. The 1,000-hour anode test ran in a small electrolyser, and the Fan and colleagues catalyst results are at catalyst level, not from a plant running on seawater.
• Many results use alkaline or simulated seawater, not raw natural seawater. Natural seawater varies with location, season, temperature and biological or chemical contamination.
• Chlorine-containing by-products, gas purity and gas crossover need measurement in each system. The sources reviewed do not give a complete accounting for these in a full seawater system.
• Membrane-based and direct-contact designs are different architectures, so their figures cannot be compared directly.
• Energy use, water pretreatment, chemical dosing, maintenance and replacement costs are needed for a fair comparison with purified-water electrolysis. The only cost figure in the sources reviewed is an estimate made by the authors of one study.
• The sources reviewed do not include independent replication of the long-duration results.

Possible future uses

Product concepts: Coastal seawater hydrogen unit

Timeline

1. 30 Nov 2022Xie and colleagues publish a membrane-based seawater electrolyser for hydrogen generation in Nature. Sources: [2]
2. 9 Feb 2024Fan and colleagues publish a paper on electrocatalytic seawater splitting at ampere-level current density in Nature Sustainability. Sources: [1]
3. 28 Nov 2024Sun and colleagues report a phosphate-intercalated NiFe anode operating for over 1,000 hours in a small alkaline seawater electrolyser, with a 1 kW-class stack demonstration. Sources: [3]
4. 28 Apr 2025Wu and colleagues publish a review of direct seawater electrolysis covering electrode designs, cell configurations and system integration. Sources: [4]

Futures this could help bring about

How far away?

Removing carbon with the ocean

Pilots · 5 of 9 steps done

Related breakthroughs

• Catalyst runs in seawater for 2,800 hours at about 1.25 A per square centimetre (9 Feb 2024)

Glossary

Electrolyser

A device that uses electricity to drive a chemical reaction, here splitting water into hydrogen and oxygen.

Electrocatalyst

A material that helps an electrode reaction proceed more readily.

Current density

Electric current per unit electrode area. A higher value can mean more hydrogen per unit area, but it does not on its own show energy efficiency.

Fouling

Unwanted material building up on a surface or in a flow path, which reduces performance.

Sources

1. peer reviewed paper
   Ultrastable electrocatalytic seawater splitting at ampere-level current density
   Rongli Fan, Changhao Liu, Zhonghua Li et al.. Nature Sustainability, 9 Feb 2024. DOI: 10.1038/s41893-023-01263-w. Accessed 21 Oct 2026.
2. peer reviewed paper
   A membrane-based seawater electrolyser for hydrogen generation
   Heping Xie, Zhiyu Zhao, Tao Liu et al.. Nature, 30 Nov 2022. DOI: 10.1038/s41586-022-05379-5. Accessed 21 Oct 2026.
3. peer reviewed paper
   Corrosion-resistant NiFe anode towards kilowatt-scale alkaline seawater electrolysis
   Xiaogang Sun, Wei Shen, Hao Liu et al.. Nature Communications, 28 Nov 2024. DOI: 10.1038/s41467-024-54754-5. Accessed 21 Oct 2026.
4. review article
   Direct seawater electrolysis for green hydrogen production: electrode designs, cell configurations, and system integrations
   Lizhen Wu, Yifan Xu, Qing Wang et al.. Energy & Environmental Science, 28 Apr 2025. DOI: 10.1039/d5ee01093d. Accessed 21 Oct 2026.

Revision history

3 changes since this profile was created.