University of Delaware (UD) engineers have demonstrated a way to effectively
capture 99% of carbon dioxide from air using a novel electrochemical system
powered by hydrogen.
It is a significant advance for carbon dioxide capture and could bring more
environmentally friendly fuel cells closer to market.
The research team, led by UD Professor Yushan Yan, reported their method in
Nature Energy on Thursday, February 3.
Game-changing tech for fuel cell efficiency
Fuel cells work by converting fuel chemical energy directly into
electricity. They can be used in transportation for things like hybrid or
zero-emission vehicles.
Yan, Henry Belin du Pont Chair of Chemical and Biomolecular Engineering at
UD, has been working for some time to improve hydroxide exchange membrane
(HEM) fuel cells, an economical and environmentally friendly alternative to
traditional acid-based fuel cells used today.
But HEM fuel cells have a shortcoming that has kept them off the road—they
are extremely sensitive to carbon dioxide in the air. Essentially, the
carbon dioxide makes it hard for a HEM fuel cell to breathe.
This defect quickly reduces the fuel cell's performance and efficiency by up
to 20%, rendering the fuel cell no better than a gasoline engine. Yan's
research group has been searching for a workaround for this carbon dioxide
conundrum for over 15 years.
A few years back, the researchers realized this disadvantage might actually
be a solution—for carbon dioxide removal.
"Once we dug into the mechanism, we realized the fuel cells were capturing
just about every bit of carbon dioxide that came into them, and they were
really good at separating it to the other side," said Brian Setzler,
assistant professor for research in chemical and biomolecular engineering
and paper co-author.
While this isn't good for the fuel cell, the team knew if they could
leverage this built-in "self-purging" process in a separate device upstream
from the fuel cell stack, they could turn it into a carbon dioxide
separator.
"It turns out our approach is very effective. We can capture 99% of the
carbon dioxide out of the air in one pass if we have the right design and
right configuration," said Yan.
So, how did they do it?
They found a way to embed the power source for the electrochemical
technology inside the separation membrane. The approach involved internally
short-circuiting the device.
"It's risky, but we managed to control this short-circuited fuel cell by
hydrogen. And by using this internal electrically shorted membrane, we were
able to get rid of the bulky components, such as bipolar plates, current
collectors or any electrical wires typically found in a fuel cell stack,"
said Lin Shi, a doctoral candidate in the Yan group and the paper's lead
author.
Now, the research team had an electrochemical device that looked like a
normal filtration membrane made for separating out gases, but with the
capability to continuously pick up minute amounts of carbon dioxide from the
air like a more complicated electrochemical system.
In effect, embedding the device's wires inside the membrane created a
short-cut that made it easier for the carbon dioxide particles to travel
from one side to the other. It also enabled the team to construct a compact,
spiral module with a large surface area in a small volume. In other words,
they now have a smaller package capable of filtering greater quantities of
air at a time, making it both effective and cost-effective for fuel cell
applications. Meanwhile, fewer components mean less cost, and more
importantly, provide a way to easily scale up for the market.
The research team's results showed that an electrochemical cell measuring 2
inches by 2 inches could continuously remove about 99% of the carbon dioxide
found in air flowing at a rate of approximately two liters per minute. An
early prototype spiral device about the size of a 12-ounce soda can is
capable of filtering 10 liters of air per minute and scrubbing out 98% of
the carbon dioxide, the researchers said.
Scaled for an automotive application, the device would be roughly the size
of a gallon of milk, Setzler said, but the device could be used to remove
carbon dioxide elsewhere, too. For example, the UD-patented technology could
enable lighter, more efficient carbon dioxide removal devices in spacecraft
or submarines, where ongoing filtration is critical.
"We have some ideas for a long-term roadmap that can really help us get
there," said Setzler.
According to Shi, since the electrochemical system is powered by hydrogen,
as the hydrogen economy develops, this electrochemical device could also be
used in airplanes and buildings where air recirculation is desired as an
energy-saving measure. Later this month, following his dissertation defense,
Shi will join Versogen, a UD spinoff company founded by Yan, to continue
advancing research toward sustainable green hydrogen.
Co-authors on the paper from the Yan lab include Yun Zhao, co-first author
and research associate, who performed experimental work essential for
testing the device; Stephanie Matz, a doctoral student who contributed to
the designing and fabrication of the spiral module, and Shimshon Gottesfeld,
an adjunct professor of chemical and biomolecular engineering at UD.
Gottesfeld was principal investigator on the 2019 project, funded by the
Advanced Research Projects Agency-Energy (ARPA-E), that led to the findings.
Reference:
Lin Shi et al, A shorted membrane electrochemical cell powered by hydrogen
to remove CO2 from the air feed of hydroxide exchange membrane fuel cells,
Nature Energy (2022).
DOI: 10.1038/s41560-021-00969-5