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by Anna Ramunni, Luca Riillo, Lisa Tizte and Teresina Ambrosio, researchers at ASTERISK partner De Nora, in Italy.
Hydrogen has become one of the most promising technologies in the global energy transition. Governments and industries increasingly see it to cut emissions in sectors that cannot easily run on electricity alone, from heavy industry to shipping and large-scale energy storage.
But hydrogen is also becoming part of a broader conversation about energy security.
Unlike fossil fuels, which are unevenly distributed and often imported across long supply chains, green hydrogen can be produced locally wherever renewable electricity is available. Wind and solar energy can be converted into storable fuel, helping countries reduce dependence on external energy sources while improving the flexibility of future energy systems.
Wind and solar energy can be converted into storable fuel, helping countries reduce dependence on external energy sources
Green hydrogen is produced through electrolysis, which uses electricity to split water into hydrogen and oxygen. When powered by renewable electricity, the process produces very low greenhouse gas emissions.
Yet there is an important question that receives less attention: where will all the water come from?
As hydrogen production expands, relying exclusively on freshwater may become difficult to justify in regions already facing increasing pressure on water resources. That challenge is driving interest in a resource that is abundant, accessible, and largely untapped for electrolysis: seawater.
Why isn’t seawater used already?
Earth’s surface and are particularly attractive for coastal industrial clusters and offshore renewable projects. But electrolysis systems do not work well with untreated seawater.
Seawater contains organic compounds and dissolved salts that interfere with electrochemical performance and accelerate material degradation. These impurities must typically be removed before entering the electrolyser.
Current anion exchange membrane (AEM) electrolysis systems, among the most promising next-generation technologies, generally operate with ultra-pure water and low concentrations of potassium hydroxide (KOH) to maintain efficiency and stability. Using seawater means moving away from these ideal conditions and redesigning materials and operating strategies accordingly.
A different route to electrolysis
Among emerging electrolysis technologies, AEM has attracted growing attention because it offers a potential path toward lower-cost hydrogen production.
One of its most important advantages is that it can operate without relying on noble metals such as platinum and iridium, which are expensive and subject to supply constraints. That creates an appealing combination: abundant seawater as a feedstock and noble-metal-free electrolysis.
In principle, this could make hydrogen production more sustainable not only from an emissions perspective, but also from a materials and resource perspective. The difficulty lies in making the system robust enough to work outside laboratory conditions.
The materials challenge
Materials that perform well in conventional alkaline electrolyses do not necessarily remain stable in seawater environments.
Nickel felt, for example, is highly resistant under strongly alkaline conditions but behaves differently around pH 8, conditions closer to seawater, which contains sodium, chloride, magnesium, and calcium salts.
Titanium presents another challenge. At lower pH values, its surface can be passivated by forming titanium oxide, reducing conductivity and limiting long-term performance. Researchers are therefore investigating protective surface layers that preserve conductivity while extending electrode lifetime.
Then there is chlorine: chloride ions naturally present in seawater compete with oxygen production at the anode. Instead of generating oxygen, the system may begin producing chlorine, reducing efficiency and creating operational complications.
Overcoming this issue requires catalysts that selectively promote oxygen evolution while suppressing competing chlorine reactions.
Building electrodes for real-world seawater operation
One approach under development focuses on designing electrode architectures that avoid noble metals altogether while maintaining electrochemical performance.
In this model, catalyst formulations are developed in collaboration with university partners and integrated directly onto engineered electrode substrates. The goal is to create systems that remain conductive, selective, and durable under seawater operating conditions.
Development begins with laboratory cells measuring approximately 5 cm² before progressing to larger electrode areas of up to 500 cm². Scaling up is essential to understand whether performance demonstrated under controlled conditions can translate into systems relevant for industrial deployment.
From offshore wind to offshore hydrogen
If these technical barriers can be overcome, seawater electrolysis could change how and where hydrogen is produced.
One possible application is integration with offshore wind farms.
Instead of transmitting electricity back to shore, renewable power could be converted directly into hydrogen using seawater at the point of generation. That would reduce dependence on freshwater resources and open new opportunities for distributed energy production.
Green hydrogen is often presented as a solution for decarbonisation and energy independence. Making it directly from seawater, using technologies that avoid the use of scarce materials, could bring those ambitions closer together.
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Some notes:
Hydrogen production from seawater using AEM technology
Why isn’t seawater widely used at present? It must be purified to remove organic matter and to prevent metal passivation.
The current state of the art for AEM involves ultra-pure KOH at low concentrations
We produce the electrodes without noble metals (we develop the formulation and apply it to the substrate), whilst the catalyst is prepared by our university partner – a project requirement – platinum-coated and iridium-coated titanium cannot be used
The electrode starts at 5 cm² and we then scale up to 500 cm²
Challenge: anodic protective layer – the electrolyte is different
Ni felt is resistant to high pH levels but not at pH 8 (which is a seawater solution containing sodium, chlorine, magnesium and calcium salts)
Below pH 8, the titanium passivates and becomes titanium oxide; special protective coatings are being evaluated to improve the electrode’s conductivity and service life
The problem with chlorides is that chlorine forms in competition with oxygen (develop a selective catalyst for oxygen evolution).
Possible applications: integration with offshore installations, including wind farms