University of Delaware 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 reported their method in Nature Energy.
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.
The research team 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.
The research group has been searching for a workaround for this carbon dioxide problem
for over 15 years.
A few years back, the researchers realized this disadvantage might actually be a solution
— for carbon dioxide removal.
The researchers 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.
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.
The researcher says that it turns out their approach is very effective.
They can capture 99% of the carbon dioxide out of the air in one pass if they have the
right design and right configuration.
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 the researchers managed to control this short-circuited fuel cell by
hydrogen.
And by using this internal electrically shorted membrane, they 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.
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, provided 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.
Scaled for an automotive application, the device would be roughly the size of a gallon
of milk, 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.
According to the researcher, 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.