Liquid metal to 'harvest' clean hydrogen from water

Researchers have created a process using liquid metals, powered by sunlight, that can produce clean hydrogen from both freshwater and seawater.

The method allows researchers to ‘harvest’ hydrogen molecules from water while also avoiding many of the limits in current hydrogen production methods.

“We now have a way of extracting sustainable hydrogen, using seawater, which is easily accessible while relying solely on light for green hydrogen production,” said lead author and PhD candidate Luis Campos.

Senior researcher Professor Kourosh Kalantar-Zadeh, from the School of Chemical and Biomolecular Engineering, said the study is a showcase of how the natural chemistry of liquid metals can create hydrogen. His team produced hydrogen with a maximum efficiency of 12.9% and is currently working to improve the efficiency for commercialisation.

“For the first proof-of-concept, we consider the efficiency of this technology to be highly competitive. For instance, silicon-based solar cells started with 6% in the 1950s and did not pass 10% till the 1990s,” Kalantar-Zadeh said.

Project co-lead Dr Francois Allioux said, “Hydrogen offers a clean energy solution for a sustainable future and could play a pivotal role in Australia’s international advantage in a hydrogen economy.”

At the technology’s heart is gallium, a metal with a low melting point, which needs less energy to transition from a solid into a liquid. Gallium particles’ ability to absorb light caught the team’s attention.

The result of this finding was a technology using a circular chemical process: particles of gallium are suspended in either seawater or freshwater and activated under sunlight or artificial light. The gallium reacts with the water to become gallium oxyhydroxide and releases hydrogen.

“After we extract hydrogen, the gallium oxyhydroxide can also be reduced back into gallium and reused for future hydrogen production — which we term a circular process,” Kalantar-Zadeh said.

At room temperature gallium looks like solid metal, but when heated to body temperature it transforms into liquid metallic puddles.

Campos said the surface of liquid gallium is very chemically ‘non-sticky’, and most materials will not attach to it under normal conditions. But when exposed to light in water, liquid gallium reacts at its surface, gradually oxidising and corroding. This reaction creates clean hydrogen and gallium oxyhydroxide on its surface.

Kalantar-Zadeh said, “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 University of Sydney-led research was published in Nature Communications. The team are now working on increasing the efficiency of the technology and their next goal is to establish a mid-scale reactor to extract hydrogen.

Image caption: Gallium, a chemical element with symbol Ga and atomic number 31. Credit: iStock.com/Igor Krasilov