More gallium the key to green hydrogen

A liquid metal being explored for use in shapeshifting soft robots and enhancing carbon-capturing properties of platinum, gallium is proving to be the missing link to many questions materials scientists have been attempting to answer for years. Now, when the need for clean alternative energy is at its peak, University of California Santa Cruz researchers have found that gallium could unlock the doors to cheap hydrogen production.

Researchers have tried to find efficient and cost-effective ways to use aluminum's reactivity to generate clean hydrogen fuel. As it is a highly reactive metal that can strip oxygen from water molecules to generate hydrogen gas, the value was immediately apparent.

However, by its very nature, when coming into contact with oxygen, it becomes coated in a layer of aluminum oxide, essentially activating a self-defense mechanism and cutting off the useful reaction of hydrogen production.

It turns out gallium was the deactivation code all along.

A new study by researchers at UC Santa Cruz has shown that an easily produced composite of gallium and aluminum creates aluminum nanoparticles that, when submerged, react as it normally does but can do so in room temperature water to yield incredible amounts of hydrogen.

"We don't need any energy input, and it bubbles hydrogen like crazy," said Scott Oliver, University of California Santa Cruz Chemistry professor and co-author of the study. "I've never seen anything like it."

The global transition away from fossil fuels is proving difficult as comparable fuels aren't nearly as cheap or easy to access as petroleum.

Nevertheless, the endeavor to find ways to power the future in a clean and conscientious way has only begun to ramp up, and one of the top prospects is through hydrogen fuel cells.

The concept is fairly simple; fuel cells work by combining hydrogen with oxygen, with the resulting chemical reaction generating energy. The process is completely emission-free, with the only byproduct being water vapor.

In principle, a fuel cell works much like a battery, except that it generates its own electricity from the hydrogen onboard rather than being charged from an external source. This means it would be capable of delivering longer driving ranges and therefore is more feasible for long-haul transportation and heavier equipment – if such a battery was to be installed in an automobile.

With many companies seeking to use hydrogen as a replacement for petroleum-based fuels, the UCSC discovery could not have come at a better time.

Gallium is the key

The hydrogen-producing reaction between aluminum and gallium with water has been known for quite some time, since the 1970s at least, with videos of the process being readily available online and easily replicable by amateur chemists and science enthusiasts.

The UC Santa Cruz discovery works because gallium, a liquid-like metal that becomes so at just above room temperature, removes the passive aluminum oxide coating, allowing the direct contact of aluminum with water.

Co-author of the study, Bakthan Singaram, said the work grew out of a conversation he had had with a student, co-author Isai Lopez, who had seen videos online and wanted to experiment with aluminum-gallium hydrogen generation in his home kitchen.

"He wasn't doing it in a scientific way, so I set him up with a graduate student to do a systematic study," said Singaram. "I thought it would make a good senior thesis for him to measure the hydrogen output from different ratios of gallium and aluminum."

Previous studies had mostly used aluminum-rich mixtures of aluminum and gallium, with some cases even using more complex alloys. But Singaram's lab found that hydrogen production increased with a gallium-rich composite, a simple ratio conversation that had seemingly been missed all these years.

The result, the rate of hydrogen production was so unexpectedly high that the researchers thought there must be something fundamentally different about this gallium-rich alloy.

Oliver suggested that the formation of aluminum nanoparticles could account for the increased hydrogen production, and as his lab had the equipment needed for nanoscale examination of the alloy, they used scanning electron microscopy and x-ray diffraction to find that the aluminum nanoparticles formed a three to one gallium-aluminum composite; the optimal ratio for hydrogen production, they found.

In this gallium-rich composite, the gallium serves both to dissolve the aluminum oxide coating as well as to separate the aluminum into nanoparticles themselves.

"The gallium separates the nanoparticles and keeps them from aggregating into larger particles," Singaram said. "People have struggled to make aluminum nanoparticles, and here we are producing them under normal atmospheric pressure and room temperature conditions."

Even better, making the composite requires nothing more than simple manual mixing.

"Our method uses a small amount of aluminum, which ensures it all dissolves into the majority gallium as discrete nanoparticles," said Oliver. "This generates a much larger amount of hydrogen, almost complete compared to the theoretical value based on the amount of aluminum. It also makes gallium recovery easier for reuse."

As the composite can be made with readily available sources of aluminum such as used foil or cans and can be stored for long periods by covering it with a chemical called cyclohexane – often used in nylon production – to protect it from moisture, combine all that with the fact the gallium is easily recovered for reuse while still yielding roughly 90% of the hydrogen that could theoretically be produced from the input aluminum and you have perhaps one of the most economical, environmentally sound, and efficient processes discovered to date in the race toward alternative energy solutions.

Although gallium is not abundant and is relatively expensive, it can be recovered and reused multiple times without losing effectiveness, Singaram added. It remains to be seen, however, if this process can be scaled up to be practical for commercial hydrogen production.

Scott Oliver and Bakthan Singaram are corresponding authors of the paper on the new findings, published in "Applied Nano Materials."

A U.S. patent application is pending on this technology.

You can read about the amazing properties of gallium at Rise of the liquid gallium smart robots and Gallium is platinum's new best friend in the November 24, 2021, and June 8, 2022, editions of Metal Tech News, respectively.

Additionally, you can find out more about hydrogen fuel cells at Volvo CE opens first hydrogen fuel cell lab in the May 26, 2021, edition of Metal Tech News.