Easy aluminum nanoparticles for rapid, efficient hydrogen generation
from water

Date:
February 18, 2022
Source:
University of California - Santa Cruz
Summary:
For years, researchers have tried to find efficient and
cost-effective ways to harness the extreme reactivity of aluminum
to generate clean hydrogen fuel. A new study shows that an easily
produced composite of gallium and aluminum creates aluminum
nanoparticles that react rapidly with water at room temperature
to yield large amounts of hydrogen.



FULL STORY ========================================================================== Aluminum is a highly reactive metal that can strip oxygen from water
molecules to generate hydrogen gas. Its widespread use in products that
get wet poses no danger because aluminum instantly reacts with air to
acquire a coating of aluminum oxide, which blocks further reactions.


==========================================================================
For years, researchers have tried to find efficient and cost-effective
ways to use aluminum's reactivity to generate clean hydrogen fuel. A
new study by researchers at UC Santa Cruz shows that an easily produced composite of gallium and aluminum creates aluminum nanoparticles that
react rapidly with water at room temperature to yield large amounts of hydrogen. The gallium was easily recovered for reuse after the reaction,
which yields 90% of the hydrogen that could theoretically be produced
from reaction of all the aluminum in the composite.

"We don't need any energy input, and it bubbles hydrogen like crazy. I've
never seen anything like it," said UCSC Chemistry Professor Scott Oliver.

Oliver and Bakthan Singaram, professor of chemistry and biochemistry,
are corresponding authors of a paper on the new findings, published
February 14 in Applied Nano Materials.

The reaction of aluminum and gallium with water has been known since the
1970s, and videos of it are easy to find online. It works because gallium,
a liquid at just above room temperature, removes the passive aluminum
oxide coating, allowing direct contact of aluminum with water. The new
study, however, includes several innovations and novel findings that
could lead to practical applications.

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



========================================================================== Singaram said the study grew out of a conversation he had with a student, coauthor Isai Lopez, who had seen some videos and started experimenting
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. I thought it would make a good senior
thesis for him to measure the hydrogen output from different ratios of
gallium and aluminum," Singaram said.

Previous studies had mostly used aluminum-rich mixtures of aluminum and gallium, or in some cases more complex alloys. But Singaram's lab found
that hydrogen production increased with a gallium-rich composite. In
fact, the rate of hydrogen production was so unexpectedly high 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 his lab had the
equipment needed for nanoscale characterization of the alloy. Using
scanning electron microscopy and x-ray diffraction, the researchers
showed the formation of aluminum nanoparticles in a 3:1 gallium-aluminum composite, which they found to be the optimal ratio for hydrogen
production.

In this gallium-rich composite, the gallium serves both to dissolve
the aluminum oxide coating and to separate the aluminum into
nanoparticles. "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."
Making the composite required 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," Oliver
said. "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." The composite can be made
with readily available sources of aluminum, including used foil or cans,
and the composite can be stored for long periods by covering it with cyclohexane to protect it from moisture.

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

First author Gabriella Amberchan is graduate student in Singaram's
lab. Other coauthors of the paper include Beatriz Ehlke, Jeremy Barnett,
Neo Bao, and A'Lester Allen, all at UCSC. This work was partially
supported by funds from the Ima Hernandez Foundation.

========================================================================== Story Source: Materials provided by
University_of_California_-_Santa_Cruz. Original written by Tim
Stephens. Note: Content may be edited for style and length.


========================================================================== Related Multimedia:
*
Bubbles_of_hydrogen_gas_are_generated_from_the_reaction_of_water_with_an
aluminum-gallium_composite ========================================================================== Journal Reference:
1. Gabriella Amberchan, Isai Lopez, Beatriz Ehlke, Jeremy Barnett,
Neo Y.

Bao, A'Lester Allen, Bakthan Singaram, Scott R. J. Oliver. Aluminum
Nanoparticles from a Ga-Al Composite for Water Splitting and
Hydrogen Generation. ACS Applied Nano Materials, 2022; DOI:
10.1021/acsanm.1c04331 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220218100644.htm

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