The ocean may hold an enormous reserve of nuclear fuel that has remained largely out of reach because uranium is present in seawater only in tiny concentrations.

Now, Chinese researchers say they have developed a new material that can capture uranium from natural seawater at more than eight times a benchmark set by the US Department of Energy (DOE).

The material, called PhosCage, was developed by scientists at the Qingdao Institute of Bioenergy and Bioprocess Technology under the Chinese Academy of Sciences.

In tests using real seawater, it recovered as much as 50.4 milligrams of uranium for every gram of material, compared with the US DOE benchmark of 6 milligrams per gram.

The result is attracting attention because researchers around the world have spent decades trying to make seawater uranium extraction efficient enough to become a realistic source of nuclear fuel.

Why the ocean is attracting attention as a uranium source

Uranium is already mined from land, but seawater contains an estimated 4.5 billion tonnes of uranium.
The problem is concentration: seawater contains only about 3.3 micrograms of uranium per litre, while countless other ions are present in much greater quantities.That makes the task less like conventional mining and more like finding a particular molecule in an enormous chemical mixture.

Researchers need materials that can identify uranium ions, capture them selectively and then release them efficiently enough for the process to make economic sense.

Marine organisms and biofilms can also interfere with materials placed in seawater for long periods.

How China’s PhosCage works

PhosCage is a phosphate-functionalised porous organic cage designed with nanoscale spaces containing phosphate groups. These groups act as chemical binding sites for uranium-bearing ions in seawater.

According to the research published in the Journal of Hazardous Materials, the material reached adsorption equilibrium in laboratory conditions in about five minutes.

Tests involving natural seawater from multiple marine areas produced a maximum uranium uptake of 50.4 mg per gram.

The researchers say the material's molecular structure helps overcome a common problem in uranium extraction: increasing the number of sites that can bind uranium can make it harder for ions to move through the material.

PhosCage was designed to improve both access to the binding sites and their ability to selectively capture uranium.

The US benchmark makes the result stand out

The headline figure comes from a comparison with a US Department of Energy benchmark of 6 mg of uranium per gram within 30 days.

At 50.4 mg/g, PhosCage reached about 8.4 times that benchmark in the researchers' natural-seawater tests.

But the comparison needs some context.

The 50.4 mg/g figure refers to the molecular PhosCage material tested in seawater. The researchers also worked on turning the material into a more practical form that could potentially be handled in marine environments.

That distinction matters because a material that performs exceptionally well as a laboratory adsorbent still has to prove that it can operate efficiently, repeatedly and economically at much larger scales.

Scientists turned the material into reusable beads

To move beyond a powder-like laboratory material, the team combined PhosCage with aramid nanofibres to create composite aerogel microspheres known as AC-POC.

In tests using natural seawater, the microspheres achieved a dynamic uranium extraction capacity of 22.55 mg per gram after 15 days, equivalent to about 3.8 times the US DOE benchmark.

Their negatively charged surfaces also helped limit microbial attachment and biofilm formation, an important consideration for materials intended for prolonged marine use.

The bead form also addresses a practical problem: loose nanoscale or powdered materials are difficult to deploy, recover and reuse in the ocean.

China’s nuclear expansion gives the research added importance

The development comes as China continues to expand its nuclear power capacity, increasing the importance of securing reliable uranium supplies.

Seawater extraction is attractive in theory because the resource is enormous and distributed across the world's oceans.

But the low concentration of uranium means that large volumes of seawater would have to be processed, making energy use, material costs, recovery efficiency and durability critical to any future commercial system.

A 2025 review of seawater uranium extraction noted that extremely low uranium concentrations, competing ions and marine biological fouling remain among the biggest barriers to moving the technology from laboratory research toward industrial deployment.

A breakthrough in the lab does not mean ocean-scale extraction yet

The new results are significant, but they do not mean China can immediately begin harvesting billions of tonnes of uranium from the ocean.

The reported experiments were conducted using natural seawater samples and laboratory-scale systems.

Researchers still need to demonstrate how the material performs during prolonged operation in real marine environments, how cheaply it can be produced, how much energy the complete extraction process requires and how efficiently the captured uranium can be recovered.

Those questions could ultimately determine whether seawater uranium extraction becomes a commercial technology or remains primarily a research goal.

Still, the Chinese team's results represent an important step.

By combining high uranium uptake with rapid adsorption and a more deployable material format, the research points toward a possible new approach to securing nuclear fuel — one in which the world's oceans could eventually become part of the uranium supply chain.