Researchers at the University of Illinois at Chicago have engineered a potentially game-changing solar cell that cheaply and efficiently converts atmospheric carbon dioxide directly into usable hydrocarbon fuel, using only sunlight for energy.
The finding is reported in the July 29 issue of Science and was funded by the National Science Foundation and the U.S. Department of Energy. A provisional patent application has been filed.
Unlike conventional solar cells, which convert sunlight into electricity that must be stored in heavy batteries, the new device essentially does the work of plants, converting atmospheric carbon dioxide into fuel, solving two crucial problems at once. A solar farm of such "artificial leaves" could remove significant amounts of carbon from the atmosphere and produce energy-dense fuel efficiently.
"The new solar cell is not photovoltaic—it's photosynthetic," says Amin Salehi-Khojin, assistant professor of mechanical and industrial engineering at UIC and senior author on the study.
"Instead of producing energy in an unsustainable one-way route from fossil fuels to greenhouse gas, we can now reverse the process and recycle atmospheric carbon into fuel using sunlight," he said.
While plants produce fuel in the form of sugar, the artificial leaf delivers syngas, or synthesis gas, a mixture of hydrogen gas and carbon monoxide. Syngas can be burned directly, or converted into diesel or other hydrocarbon fuels.
The ability to turn CO2 into fuel at a cost comparable to a gallon of gasoline would render fossil fuels obsolete.
Chemical reactions that convert CO2 into burnable forms of carbon are called reduction reactions, the opposite of oxidation or combustion. Engineers have been exploring different catalysts to drive CO2 reduction, but so far such reactions have been inefficient and rely on expensive precious metals such as silver, Salehi-Khojin said.
"What we needed was a new family of chemicals with extraordinary properties," he said.
Salehi-Khojin and his coworkers focused on a family of nano-structured compounds called transition metal dichalcogenides—or TMDCs—as catalysts, pairing them with an unconventional ionic liquid as the electrolyte inside a two-compartment, three-electrode electrochemical cell.
The best of several catalysts they studied turned out to be nanoflake tungsten diselenide.
"The new catalyst is more active; more able to break carbon dioxide's chemical bonds," said UIC postdoctoral researcher Mohammad Asadi, first author on the Science paper.
In fact, he said, the new catalyst is 1,000 times faster than noble-metal catalysts—and about 20 times cheaper.
Other researchers have used TMDC catalysts to produce hydrogen by other means, but not by reduction of CO2. The catalyst couldn't survive the reaction.
"The active sites of the catalyst get poisoned and oxidized," Salehi-Khojin said. The breakthrough, he said, was to use an ionic fluid called ethyl-methyl-imidazolium tetrafluoroborate, mixed 50-50 with water.
"The combination of water and the ionic liquid makes a co-catalyst that preserves the catalyst's active sites under the harsh reduction reaction conditions," Salehi-Khojin said.
The UIC artificial leaf consists of two silicon triple-junction photovoltaic cells of 18 square centimeters to harvest light; the tungsten diselenide and ionic liquid co-catalyst system on the cathode side; and cobalt oxide in potassium phosphate electrolyte on the anode side.
When light of 100 watts per square meter - about the average intensity reaching the Earth's surface - energizes the cell, hydrogen and carbon monoxide gas bubble up from the cathode, while free oxygen and hydrogen ions are produced at the anode.
"The hydrogen ions diffuse through a membrane to the cathode side, to participate in the carbon dioxide reduction reaction," said Asadi.
The technology should be adaptable not only to large-scale use, like solar farms, but also to small-scale applications, Salehi-Khojin said. In the future, he said, it may prove useful on Mars, whose atmosphere is mostly carbon dioxide, if the planet is also found to have water.
"This work has benefitted from the significant history of NSF support for basic research that feeds directly into valuable technologies and engineering achievements," said NSF program director Robert McCabe.
"The results nicely meld experimental and computational studies to obtain new insight into the unique electronic properties of transition metal dichalcogenides," McCabe said. "The research team has combined this mechanistic insight with some clever electrochemical engineering to make significant progress in one of the grand-challenge areas of catalysis as related to energy conversion and the environment."
Explore further:
Ionic liquid catalyst helps turn emissions into fuel
More information:
Nanostructured transition metal dichalcogenide electrocatalysts for CO2 reduction in ionic liquid, Science, science.sciencemag.org/cgi/doi/10.1126/science.aaf4767

antialias_physorg
3.9 / 5 (16) Jul 28, 2016Not sure about that. While you can probably get some fuel out of the (very thin) CO2 atmosphere you have to have oxygen to burn that fuel again.
As the famous last words of some unsung SciFi roleplayer go:
"We take our flamers, go down to the planet and torch the alien queen!....Whaddaya mean 'no oxygen in the atmosphere'?"
gregd
1.7 / 5 (15) Jul 28, 2016epoxy
Jul 28, 2016pntaylor
not rated yet Jul 28, 2016"The hydrogen ions diffuse through a membrane to the cathode side, to participate in the carbon dioxide reduction reaction," "
So what happens to the carbon monoxide???
greenonions
4.3 / 5 (6) Jul 28, 2016Eikka
5 / 5 (9) Jul 28, 2016Tell me, what becomes of CO2 when you remove the carbon?
Whydening Gyre
4.5 / 5 (8) Jul 28, 2016(My bio-chemist daughter is an alum.:-))
moops
3.7 / 5 (3) Jul 28, 2016precisely. This process produces both fuel and oxygen. Both must be stored but that is essentially the narrative. we just happen to live on a planet with lots of excess O2 in the atmosphere so we don't need to carry that part.
but, a battery looks much more practical for Mars. If I have to store and carry my oxygen and fuel then the benefits of energy-dense hydrocarbon is pretty much nullified.
marcomatto
5 / 5 (3) Jul 28, 2016Isn't that what trees do?
Eikka
5 / 5 (4) Jul 28, 2016It's the same thing for batteries as well. It's just not oxygen that does the "oxidizing" but another chemical, and that other chemical is often much heavier than plain old oxygen.
retrosurf
5 / 5 (3) Jul 28, 2016That's part of the fuel they're talking about. You feed the hydrogen and carbon monoxide into the Fischer-Tropsch process, and you get higher molecular weight carbon-based fuels out of it.
Eikka
5 / 5 (2) Jul 28, 2016And on another point, if you're going to manufacture it from local materials, it's easier to pull oxygen from air than mine for minerals underground.
antialias_physorg
3.5 / 5 (8) Jul 28, 2016The system they have doesn't capture the oxygen.
RichManJoe
5 / 5 (2) Jul 28, 2016Whydening Gyre
4.5 / 5 (8) Jul 28, 2016That's always the case in the beginning. Scale it up and see what happens...
Whydening Gyre
4.3 / 5 (6) Jul 28, 2016A fancy air-freshener?
(Not too loud - Dyson might use it to purify your home atmosphere...)
Phys1
4.4 / 5 (7) Jul 28, 2016On Mars there is no free oxygen and this technology can produce it.
Phys1
4.6 / 5 (10) Jul 28, 2016I guess you missed the point. None.
Spoken like a true visionary.
"All new technologies are nonsense, it's never going to work."
kochevnik
2 / 5 (8) Jul 28, 2016Direct sunlight gives about 900watts/m^2
DonGateley
5 / 5 (1) Jul 28, 2016gkam
2.3 / 5 (12) Jul 28, 2016---------------------------------------
O2
Da Schneib
4.6 / 5 (10) Jul 28, 2016Whydening Gyre
4.5 / 5 (8) Jul 28, 2016One problem ( on earth, anyway) - what happens if we run out of CO2?
And with all that extra oxygen in the air, stuff will burn better...:-)
mikael_murstam
5 / 5 (2) Jul 28, 2016It produces oxygen.
big_hairy_jimbo
5 / 5 (3) Jul 28, 2016Mars light intensity also seems favourable with minimum Solar radiation being 492 W/m2 (according to Wiki). I think this device will definitely come in handy :-)
Wonder how it would go with solar concentrators. What affect does temperature have on the system?
wolfdaddy74701
3 / 5 (4) Jul 29, 2016rrrander
1.5 / 5 (8) Jul 29, 2016antialias_physorg
3.5 / 5 (8) Jul 29, 2016That's the twist:
Either you use this for producing oxygen for breathing purposes - in which case the entire hydrocarbon fuel part is a waste since you have no oxygen left to burn it..or must implement yet another process to create oxygen so that you can burn this stuff.
Creating oxygen is something we'd want to do on Mars. But I'm fairly certain that if we drop the entire 'hydrocarbon fuel' angle from the design specs of a system that there is some more efficient way to do it.
Hydrocarbon fuels are also very inefficient when burned. Going for a closed hydrogen/oxygen-H2O fuelcell cycle (or just batteries) seems a lot more efficient use of solar power for moving stuff about.
greenonions
4.3 / 5 (6) Jul 29, 2016And of course - we have wind; geothermal; wave; tidal; hydro; otec; nuclear; bio-fuels; conservation etc. etc. etc.
Phys1
4 / 5 (4) Jul 29, 2016Water is another limitation. In the end you will convert O2 into CO2 by breathing so CO2 needs to be recovered .
Eikka
5 / 5 (3) Jul 29, 2016Getting oxygen is not going to be very hard - it's everywhere around. Take for example, what is sand? SiO2
Producing metals out of the martian soil is going to give you a big waste stream of oxygen anyways because the mineral ores are all oxides. Plain rock is full of oxygen. Getting nitrogen for breathable air is going to be the bigger problem.
Carbon pulled from the atmosphere is also useful for chemically reducing the metals from their ores.
Eikka
5 / 5 (4) Jul 29, 2016BongThePuffin
4 / 5 (8) Jul 29, 2016That's pretty naive. It depends how you remove the carbon.
gkam
1.3 / 5 (7) Jul 29, 2016I used an eraser.
How would you do it?
Whydening Gyre
4.2 / 5 (5) Jul 29, 2016What you actually get is 2 ea. Oxygen atoms... (No carbon to bind them)
And George - that last ba-dmp-bmp was pretty lame...:-)
Whydening Gyre
4.2 / 5 (5) Jul 29, 2016My reference for this is the 1st "Total Recall"...:-)
gkam
1 / 5 (5) Jul 29, 2016Yeah, . . .
Phys1
3 / 5 (2) Jul 30, 2016If you have to produce silicon in order to breathe you have a big problem :-) .
Eikka
5 / 5 (2) Jul 30, 2016The oxygen is not consumed by breathing it. It returns as CO2 which is recycled back by the plants used to make all the food the population eats. For a given population of people, you will only need to add a certain amount of oxygen once and then simply replace what leaks out.
The oxygen gained from minerals and metals extraction is surplus. Same as with pulling CO2 out of the atmosphere to turn it into fuel - the oxygen released on the side is surplus and free to use to later oxidize the fuel for energy.
Phys1
3.7 / 5 (3) Jul 30, 2016That is how it is on Earth. What makes you think it is viable to grow plants on Mars just for the sake of producing oxygen ? It will take a lot more than you can eat.
Eikka
3.7 / 5 (3) Jul 31, 2016How do you think of having a colony on mars if you can't grow your own food there? It's pretty much assumed you can, or you won't be going there anyhow because the logistics of continuous supply from earth is just too damn expensive.
Growing enough food for you to eat releases exactly the amount of oxygen needed for you to metabolize that same food, and there will actually be an excess of oxygen because parts of the plants are inedible. The excess carbon and oxygen have to be burned to keep enough CO2 in the system for the plants to grow.
tear88
5 / 5 (1) Jul 31, 2016I had a similar reaction on reading "The finding ... was funded by the National Science Foundation and the U.S. Department of Energy. A provisional patent application has been filed.".
Any patent should give EVERYONE the right to use the technology.
There's something similar going on with the DeVAP HVAC technology; controlled by the government, with no visible progress in rollout.
tear88
5 / 5 (1) Jul 31, 2016What are these "trees" of which you speak? Oh, wait, I think I saw one recently. In a museum.
I wonder which process is a) more environmentally friendly and b) faster. Who knows, maybe we can erect roofs equipped with this new invention, over the parking lots.
PoppaJ
4 / 5 (4) Jul 31, 2016aksdad
2 / 5 (4) Aug 01, 2016But it didn't say this method could actually do it, or even has the potential to do it, at a cost comparable to manufacturing gasoline from oil.
Phys1
1 / 5 (1) Aug 01, 2016How did you get the idea that I think this?
Dug
3 / 5 (2) Aug 01, 2016"The ability to turn CO2 into fuel at a cost comparable to a gallon of gasoline would render fossil fuels obsolete."
There's and economic catch here. The source of ethyl-methyl-imidazolium tetrafluoroborate is... wait for it... the petro-chemical industry. The petro-chemical industry (about 5% of the total petroleum industry) is economically dependent on the economy-of-scale of the petroleum industry. The bulk of the petroleum industry is transportation and heating fuels. Doing away with petroleum fuels while great for the environment will have huge down stream economic/cost increase impacts on the petro-chemical industry including food production, pharma, plastics and the synthesis of ethyl-methyl-imidazolium tetrafluoroborate. So, like biofuels it turns out the process to get rid of petroleum is also economically dependent on the petroleum.
greenonions
3 / 5 (2) Aug 01, 2016ka_
4 / 5 (1) Aug 01, 2016humy
3.2 / 5 (5) Aug 02, 2016yes.
This is because making hydrogen biofuel is a deeply flawed strategy and only in part because each molecule of H2 leaked into the atmosphere, and there would inevitably be wide spread leakage if the so called "hydrogen economy" is ever realized, has many time the greenhouse effect as each molecule of CO2.
If the whole point of this is to stop global warming, its a non-starter.
Plus efficient compact H2 storage is a major issue.
Plus it is unsafe as it easily explodes if accidental mixed with air in an accident; -you certainly wouldn't want your cars to store H2 in a car pile up!
Much better to stick to other types of renewables.
ka_
4 / 5 (1) Aug 02, 2016DonGateley
4.5 / 5 (2) Aug 02, 2016If it's done locally all kinds of new cycles and dynamics could ensue and we won't be any better off than we were. If even.
lengould100
5 / 5 (1) Aug 03, 2016"Hydrogen storage in cars is a problem"? Reliable reference please. Most recent tests I've seen results for have proven that stored hydrogen is no more explosive than gasoline, and when the tank is breached (needed a 50 cal. rifle to do it) the hydrogen just leaks straight up, damaging pretty much nothing, whereas gasoline fro a ruptured fuel tank flows down under the vehicle, just waiting to cook the occupants.
All your rest the same.
Invest in oil much?