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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. Scientists have described 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: 3:1
in favor of gallium.
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 a lot more abundant and easier to get
hold of than gallium as it can be sourced from recycled materials. But in this
process, gallium it can be recovered and reused many times over without losing
its effectiveness. That's yet another factor in favor of the new technique.
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 published paper.
Reference: Research paper