A new type of solar-powered technology has the potential to play a big role in the fight against climate change if its inventors can take it from the laboratory to industrial-scale use.
On Thursday, a team of scientists announced in the journal Science that they have created a device that absorbs carbon dioxide from the atmosphere and uses sunlight to break it into a mix of carbon monoxide and hydrogen called synthesis gas or “syngas,” that can be used directly or turned into diesel or other liquid fuels, said Amin Salehi-Khojin, a mechanical engineer at the University of Illinois at Chicago who leads the lab that conducted the research.
The team aims to produce fuel at about $2 a gallon, he said, a price that would be cost-competitive with gasoline and, in his opinion, make drilling for oil or gas obsolete.
Although burning such a transportation fuel would release the carbon back into the atmosphere, it could be considered a carbon-neutral energy source. That’s because that carbon would have been removed from the atmosphere to make the syngas, thus producing no new emissions.
“This is a real artificial leaf, ” Salehi-Khojin said. Where plants use sunlight to power photosynthesis, absorbing CO2 and turning it into sugar for energy, “we use the energy from the sun, and by CO2 remediation, we store the energy of the sun in the chemical bonds” of the syngas.
“The beauty of this work is it directly uses the energy of the sun. This doesn’t need any electricity or external energy,” said Mohammad Asadi, the study’s lead author and a researcher in Salehi-Khojin’s lab.
So far the team has created a working prototype of the device on a small scale, using artificial sunlight and a direct source of CO2 to study and optimize the chemical process, said Salehi-Khojin, who said a provisional patent has been filed for the technology. The Department of Energy and the National Science Foundation funded the research.
“In terms of the size of the setup, we have used 100 square centimeters of the catalyst,” Asadi said. “We need to make it bigger than this to take it to the industrial scale.” He envisions a “solar park” that would draw CO2 out of the atmosphere, as well as smaller installations attached to power plants and industrial facilities to capture their CO2 emissions.
The Intergovernmental Panel on Climate Change considers this sort of innovation—sometimes called “negative emissions” or carbon capture and storage technology—crucial to averting extreme climate change. Under the Paris agreement signed this year, nations pledged to keep global temperature increases below 2 degrees Celsius (3.6 degrees Fahrenheit). But the amount of carbon dioxide already in the atmosphere all but guarantees that temperatures will rise at least 1.5 degrees above historic norms in the coming century.
Global temperatures are already about 0.9 degrees Celsius above those of preindustrial times.
There are many efforts underway to expand carbon-neutral or negative emissions technologies, such as an Icelandic pilot project that is converting power plant emissions into stone. There’s even a Carbon X Prize competition under way, with a $20 million payoff for the winning team. But most of these projects focus on storing emissions from smokestacks, rather than dealing with the carbon already in the atmosphere.
The cost and amount of energy consumed by such storage technologies can be high, decreasing the carbon benefits, said Doug Vine, an energy policy analyst and a senior energy fellow at the Center for Climate and Energy Solutions, an Arlington, Virginia, nonprofit.
“If you can get economic value—if you do it in an efficient way—it takes less energy, and if you can create a product that has economic value that can compensate for the costs of putting the technology on the power plant or industrial facility,” he said, “it makes it more likely that we’re going to get more carbon capture and storage deployed.”
“I know that we want to see emissions peaking soon—by the early 2020s is basically what the IPCC is saying, so that we stay on this track to stay below 2 degrees,” Vine added. “We need to pursue lots of options is the consensus. It’s not going to be one technology that solves the problem but a combination of technologies, more than likely.”
Salehi-Khojin and his team believe the artificial leaf device is promising because it is highly energy efficient and inexpensive. The reason is that the device’s chemical catalyst—necessary for breaking down the CO2—is not a costly metal such as platinum, palladium, or silver but a “nanoflake tungsten diselenide.”
This nano-compound catalyst, developed in Salehi-Khojin’s lab, proved 1,000 times more energy efficient than a traditional catalyst, he said.
“The material that they found, it reacts with CO2 in two ways. In order to convert CO2 to CO, you have to essentially break some bonds and make some bonds. This material does this more efficiently than previous ones did,” said study coauthor Larry Curtiss, a computational chemist at the Argonne National Laboratory.
“The key thing is it can transfer electrons more efficiently, because you have to add an electron, and that’s hard to do, and break the carbon-oxygen bonds,” said Curtiss, “and that’s a very strong bond. The tungsten diselenide is able to both break the bond and add the electron.”
Salehi-Khojin’s lab also came up with an unusual electrolyte, the “liquid in which the reactions take place,” Curtiss said, that “seemed to play an important role, in this case, in getting the CO2 to the surface of the tungsten diselenide, where it gets an electron added.”
The team is considering both grants and outside investments to fund the next stage of work, said Salehi-Khojin. “We need collaborators from industry to scale up the system, because that will need different expertise in terms of the manufacturing,” he said. “Maybe we need to optimize the geometries and the design—all that sort of stuff.”
Salehi-Khojin thinks the team could achieve a commercial-scale artificial leaf in two to three years. But Curtiss noted that getting an experimental technology to market can take longer still. “I have been involved in the development of new materials for batteries, for electric vehicles,” he said. “The time from when we developed at the lab scale to when it was actually incorporated into an electric vehicle was about 15 years.”
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