A research team at
MIT
has discovered a simple, low-cost, sustainable method for creating clean
hydrogen — with just seawater, soda cans and caffeine.
The team of engineers found that when the aluminum in soda cans is exposed in
its pure form and mixed with seawater, the solution bubbles up and naturally
produces hydrogen — a versatile gas that can be used to power an engine or fuel
cell without generating carbon emissions. What the team also discovered is that
this simple reaction can be sped up by adding a common stimulant: caffeine.
When exposed to air or water, pure aluminum instantly forms a protective,
aluminum-oxide skin that keeps it from reacting with water: “This is why when
you put a soda can in water, it doesn’t react,”
explains
Aly Kombargi — a PhD student in
MIT’s Department of Mechanical Engineering and lead author of the study.
As described in Cell Reports Physical
Science,
the researchers were able to prevent this reaction and produce hydrogen gas by
dropping pre-treated, pebble-sized aluminum pellets into a beaker of filtered
seawater. The aluminum was pre-treated with a rare-metal alloy — a mix of
gallium and indium — that prevents the formation of aluminum oxide,
leaving pure aluminum that can react with seawater to generate hydrogen. The
salt ions in the seawater can in turn attract and recover the alloy, which can
be reused to generate more hydrogen, in a closed loop.
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The team found that while this reaction between aluminum and seawater
successfully produces hydrogen gas, it was a slow process. On a lark, they added
coffee grounds to the mix and were surprised to see that it sped up the
reaction. Turns out, a low concentration of imidazole, an active ingredient
in caffeine, is enough to significantly speed up the reaction — producing the
same amount of hydrogen in just five minutes, compared to two hours without the
stimulant.
The researchers are developing a small reactor that could run on a marine vessel
or underwater vehicle. The vessel would hold a supply of aluminum pellets
(recycled from old soda cans and other aluminum products), along with a small
amount of the gallium-indium mix and caffeine. These ingredients could be
periodically funneled into the reactor, along with some of the surrounding
seawater, to produce hydrogen on demand — which could then power an onboard
engine or generate electricity to power the ship.
“This is very interesting for maritime applications like boats or underwater
vehicles, because you wouldn’t have to carry around seawater — it’s readily
available,” Kombargi says. “We also don’t have to carry a tank of hydrogen.
Instead, we would transport aluminum as the ‘fuel,’ and just add water to
produce the hydrogen that we need.”
Pitfalls of conventional hydrogen production and use
A fully decarbonized energy system will require both clean electrification and
low-carbon fuels, and clean hydrogen holds great
promise
in enabling us to achieve a net-zero future — if we are able to efficiently and
effectively scale its production. Hydrogen is increasingly seen as a potential
substitute for fossil
fuels,
especially in energy-intensive processes that cannot easily be fueled by
electricity — such as blast furnaces, cement works and industrial heating — and
long-distance aviation and shipping.
But until now, hydrogen has had to be manufactured — usually by separating it
from
methane,
which requires a lot of energy — which means it is only as clean as the energy
sources used to make it. Most of the 70 million tons of hydrogen currently used
globally each year by industry is derived from fossil fuels, giving it a large
carbon footprint.
Energy companies such as Vattenfall are demonstrating the promise and
viability of fossil-free
hydrogen,
but the International Energy Agency estimates we’ll need a six-fold
increase in clean hydrogen
production
to achieve net zero by 2050.
The research team — led by Douglas
Hart, MIT professor of
mechanical engineering — is developing efficient, sustainable methods to produce
hydrogen gas. The study’s co-authors also include Enoch
Ellis, an undergraduate in chemical
engineering; and Peter Godart, who
earned his Mechanical Engineering PhD at MIT in 2021 and has co-founded Found
Energy — a startup that recycles aluminum as a
source of hydrogen fuel.
One barrier to fueling vehicles with hydrogen at scale is that some designs
would require the gas to be carried onboard, like gasoline in a tank — a risky
setup, given hydrogen’s volatile potential. Hart and his team have looked for
ways to power vehicles with hydrogen without having to constantly transport the
gas itself. Their aluminum-seawater-caffeine process is a promising workaround;
but viability of the new system at scale would require a significant supply of
gallium-indium, which is relatively expensive and rare.
“For this idea to be cost-effective and sustainable, we had to work on
recovering this alloy post-reaction,” Kombargi says.
Closing the loop
The team found they could retrieve and reuse gallium-indium using a solution of
ions, which protect the metal alloy from reacting with water and help it to
precipitate into a form that can be scooped out and reused.
“Lucky for us, seawater is an ionic solution that is very cheap and available,”
said
Kombargi, who was able to duplicate the results with seawater from a nearby
beach.
The researchers believe they have discovered the recipe for running a
sustainable hydrogen reactor, which they plan to test first in marine and
underwater vehicles. They’ve calculated that such a reactor — holding about 40
pounds of aluminum pellets — could power a small, underwater glider for roughly
30 days by pumping in surrounding seawater and generating hydrogen to power the
motor.
“We’re showing a new way to produce hydrogen fuel, without carrying hydrogen but
carrying aluminum as the ‘fuel,’” Kombargi says. “The next part is to figure out
how to use this for trucks, trains and maybe airplanes. Perhaps, instead of
having to carry water as well, we could extract water from ambient
humidity
to produce hydrogen. That’s down the line.”
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Sustainable Brands Staff
Published Aug 8, 2024 8am EDT / 5am PDT / 1pm BST / 2pm CEST