31 August 2022
Bubbles of hydrogen gas are generated from the reaction of water with an aluminum-gallium composite. (Amberchan et al., Applied Nano Materials, 2022)
Hydrogen fuel promises to be a clean and abundant source of energy in the future – as long as scientists can figure out ways to produce it practically and cheaply, and without fossil fuels.
A new study provides us with another promising step in that direction, provided you can make use of existing supplies of post-consumer aluminum and gallium.
In the new research, scientists describe a relatively simple method involving aluminum nanoparticles that are able to strip the oxygen from water molecules and leave hydrogen gas.
The process yields large amounts of hydrogen, and it all works at room temperature.
That removes one of the big barriers to hydrogen fuel production: the large amounts of power required to produce it using existing methods.
This technique works with any kind of water, too, including wastewater and ocean water.
“We don’t need any energy input, and it bubbles hydrogen like crazy,” says materials scientist Scott Oliver from the University of California, Santa Cruz (UCSC).
“I’ve never seen anything like it.”
Key to the process is the use of gallium metal to enable an ongoing reaction with the water. This aluminum-gallium-water reaction has been known about for decades, but here the team optimized and enhanced it in a few particular ways.
With the help of scanning electron microscopy and X-ray diffraction techniques, the researchers were able to find the best mix of aluminum and gallium for producing hydrogen with the greatest efficiency: a 3:1 gallium-aluminum composite.
The gallium-rich alloy does double duty in both removing aluminum’s oxide coating (which would ordinarily block the reaction with water) and in producing the aluminum nanoparticles that enable faster reactions.
“The gallium separates the nanoparticles and keeps them from aggregating into larger particles,” says Bakthan Singaram, a professor of organic chemistry at UCSC.
“People have struggled to make aluminum nanoparticles, and here we are producing them under normal atmospheric pressure and room temperature conditions.”
The mixing method isn’t complicated, the researchers report, and the composite material can be stored for at least three months when submerged in cyclohexane to protect it from moisture, which would otherwise degrade its efficacy.
Aluminum is easier to get hold of than gallium as it can be sourced from post-consumer materials, such as discarded aluminum cans and foil.
Gallium is more expensive and less abundant, but in this process at least it can be recovered and reused many times over without losing its effectiveness.
There is still work to do, not least in making sure this can be scaled up from a lab set-up to something that can be used on an industrial scale. However, the early signs are that this is another method that has a lot of potential for hydrogen fuel production.
“Overall, the Ga-rich Ga−Al [gallium-rich gallium-aluminum] mixture produces substantial amounts of hydrogen at room temperature with no energy input, material manipulation, or pH modification,” the researchers conclude in their paper.
The research has been published in Applied Nano Materials.
