Australian scientists claim breakthrough in making green hydrogen from seawater and freshwater

Researchers from the University of Sydney say they have created a process that uses liquid metals and sunlight to produce green hydrogen from both freshwater and seawater.

Green hydrogen – hydrogen produced using only renewable sources – has been the focus of researchers and scientists across the globe looking to decarbonise hard-to-abate sectors like transport, manufacturing, agriculture, and major industry.

But even though the process of producing green hydrogen is well known, and predominantly focused on splitting water using methods such as electrolysis, photocatalysis, and plasma (artificial lightning), there are nevertheless a number of obstacles to this method that often lead to high costs or low yields.

One is cost, and the competition with batteries for a number of sectors such as passenger vehicles, and the other has been access to fresh water.

That’s where the new research from Professor Kourosh Kalantar-Zadeh, from the School of Chemical and Biomolecular Engineering, and his team at the University of Sydney come in, having developed a circular process that uses a liquid metal known as gallium to “harvest” hydrogen molecules from both freshwater and seawater.

Gallium is a metal with a low melting point, meaning that it needs less energy to transition from a solid into a liquid. For example, while gallium looks like a solid metal at room temperature, when heated to body temperature it transforms into liquid metallic puddles.

Lead author and PhD candidate Luis Campos describes the surface of liquid gallium as very chemically “non-sticky”, with most materials unable to attach to it under normal conditions.

But when gallium is suspended in water and exposed to light, the liquid metal reacts at its surface, gradually oxidising and corroding and then creating clean hydrogen and gallium oxyhydroxide on its surface.

Importantly, once the hydrogen is extracted, “the gallium oxyhydroxide can also be reduced back into gallium and reused for future hydrogen production – which we term a circular process,” explained Professor Kalantar-Zadeh.

“Gallium has not been explored before as a way to produce hydrogen at high rates when in contact with water – such a simple observation that was ignored previously.”

The research, which was published in the journal Nature Communications, currently boasts a maximum efficiency of 12.9 per cent.

“For the first proof-of-concept, we consider the efficiency of this technology to be highly competitive,” said Professor Kalantar-Zadeh.

“For instance, silicon based solar cells started with six percent in the 1950s and did not pass 10 per cent till the1990s.”

In addition to working to improve the efficiency for commercialisation, the University of Sydney team will also work towards establishing a mid-scale reactor to extract hydrogen.