A light-activated liquid metal process developed at the University of Sydney is offering a different way to think about green hydrogen production. The research, led by Professor Kourosh Kalantar-Zadeh from the School of Chemical and Biomolecular Engineering, explores how liquid gallium can drive hydrogen generation directly from both freshwater and seawater under illumination. The study reports a circular chemical system in which gallium particles react with water to release hydrogen and are subsequently regenerated for reuse.
Campos, L. G. B., Allioux, F.-M., Fimbres Weihs, G., Sarina, S., P. O’Mullane, A., Daeneke, T., Kaner, R. B., & Kalantar-Zadeh, K. (2026). Low temperature and rapid photothermal oxidation of liquid gallium for circular hydrogen production. Nature Communications. https://doi.org/10.1038/s41467-026-68664-1
Hydrogen has long been positioned as a potential component of low-carbon energy systems. When used as a fuel, it produces water rather than carbon dioxide at the point of use. The difficulty lies in how hydrogen is produced. Most global hydrogen supply today is derived from fossil fuels through steam methane reforming, a process that emits substantial CO₂. Green hydrogen, by contrast, is generated from water using renewable energy. The most established route is electrolysis, where electricity splits water into hydrogen and oxygen. While effective, electrolysis systems typically require purified water and significant electrical input, both of which add cost and infrastructure requirements.
Professor Kourosh Kalantar-Zadeh from University of Sydney stated,
“There is a global need to commercialize a highly efficient method for producing green hydrogen. Our process is efficient and easy to scale up.”
The University of Sydney team has taken a different approach. Instead of relying on electrical current, their system uses light to initiate surface reactions on microscopic droplets of liquid gallium suspended in water. Gallium is a metal that melts at around 29.8 degrees Celsius, slightly above room temperature. In liquid form it presents a reflective surface and displays chemical behavior that differs from many conventional solid metals.
In the reported experiments, gallium particles were dispersed in water and exposed to sunlight or artificial light sources. Under illumination, the metal surface undergoes oxidation, reacting with water to form gallium oxyhydroxide while releasing hydrogen gas. The process occurs at relatively low temperatures compared with many thermochemical hydrogen production methods. According to the authors, the system achieved a peak hydrogen production efficiency of 12.9 percent in early proof-of-concept trials.
One of the more notable aspects of the work is its compatibility with seawater. Many water-splitting technologies perform best with deionized or highly purified water, as dissolved salts and impurities can degrade electrodes or interfere with catalytic surfaces. Access to freshwater can also be a constraint in arid regions where renewable energy resources such as solar irradiation are abundant. By demonstrating hydrogen production directly in seawater, the gallium system potentially reduces the need for extensive pre-treatment infrastructure and allows hydrogen generation closer to coastal industrial hubs.
The chemistry of gallium plays a central role. Under normal conditions, liquid gallium forms a thin oxide layer that stabilizes its surface and limits further reaction. The research team observed that when the metal is illuminated in water, photothermal effects accelerate surface oxidation. The controlled corrosion releases hydrogen while forming gallium oxyhydroxide as a by-product. Importantly, that compound can be chemically reduced back to metallic gallium, enabling a circular reaction pathway. In principle, this recyclability allows the same gallium feedstock to be used repeatedly, provided the regeneration step is energy-efficient.
The concept of circularity is central to assessing the system’s practical viability. While hydrogen is generated without direct electrical input during the light-driven step, energy is still required to regenerate gallium from gallium oxyhydroxide. A full energy balance will therefore depend on the efficiency of that reduction stage and the overall integration of the process with renewable energy sources. Life-cycle analysis and techno-economic modeling will be necessary to compare the system with established photovoltaic-electrolysis combinations.
Co-lead author Dr. Francois-Marie Allioux and doctoral researcher Luis G. B. Campos describe the technology as scalable in principle. The reaction occurs at the interface of dispersed droplets, meaning that increasing surface area through optimized particle size distribution could enhance hydrogen output. The next stage for the team involves constructing a mid-scale reactor to evaluate performance beyond laboratory glassware. Reactor design will likely focus on light penetration, heat management, fluid mixing, and efficient gas capture.
The broader research context includes growing global investment in hydrogen as part of decarbonization strategies. Countries with high solar and wind resources, including Australia, have outlined ambitions to export green hydrogen or its derivatives such as ammonia. For such ambitions to be economically viable, hydrogen production must reach higher efficiencies and lower capital costs. Alternative approaches that reduce dependence on scarce materials or complex electrolyzer stacks are therefore of interest.
Gallium itself is not an abundant bulk metal, and it is currently used in electronics and semiconductor manufacturing. Any large-scale hydrogen application would require careful consideration of material supply chains and recycling strategies. However, because the process is circular and gallium is not consumed permanently, the net material demand may be manageable if recovery rates remain high.
The study contributes to a broader shift in hydrogen research toward hybrid photochemical systems that combine materials science with solar energy harvesting. Rather than converting sunlight to electricity first and then to chemical energy, the liquid gallium system couples light absorption directly to chemical transformation. This approach resembles certain photocatalytic water-splitting concepts but relies on the intrinsic properties of a liquid metal surface rather than on immobilized semiconductor catalysts.
As with many early-stage energy technologies, the key questions now concern durability, long-term stability, and cost per kilogram of hydrogen produced. Laboratory efficiency figures are informative but must be validated under continuous operation. Salt accumulation, by-product management, and gallium regeneration cycles will influence real-world performance. Integration with solar concentrators or large-area illumination systems may also affect capital expenditure.
The University of Sydney team frames its findings as an initial demonstration rather than a finished solution. By showing that liquid gallium can drive hydrogen production under light exposure in both fresh and seawater, the researchers have introduced a new pathway into the green hydrogen landscape. Whether that pathway evolves into industrial deployment will depend on engineering optimization, materials availability, and comparative economics against maturing electrolysis technologies.
In the context of energy systems engineering, the work is a reminder that unconventional material behaviors can open alternative routes to established goals. Hydrogen production has been studied for decades, yet incremental advances in surface chemistry and photothermal effects continue to reshape the field. The liquid gallium process does not eliminate the need for rigorous systems analysis, but it expands the range of options available for converting abundant solar energy into transportable chemical fuel.
Adrian graduated with a Masters Degree (1st Class Honours) in Chemical Engineering from Chester University along with Harris. His master’s research aimed to develop a standardadised clean water oxygenation transfer procedure to test bubble diffusers that are currently used in the wastewater industry commercial market. He has also undergone placments in both US and China primarely focused within the R&D department and is an associate member of the Institute of Chemical Engineers (IChemE).
