Published on August 22nd, 2016 | by Tina Casey0
New “Artificial Leaf” Solar Cell Upcycles Atmospheric CO2 For Sustainable Fuel
August 22nd, 2016 by Tina Casey
CleanTechnica spills a lot of ink on solar cell efficiency, but there is another important angle to the solar revolution that doesn’t get quite as much attention. That’s the “artificial leaf” concept, in which solar energy touches off a chemical reaction that produces a usable fuel. If that starts ringing some bells, you’re probably thinking about that time you learned about the natural process of photosynthesis in high school.
In the latest development, researchers at the University of Illinois at Chicago have tweaked Mother Nature to capture and recycle atmospheric carbon dioxide, with an assist from researchers at Argonne National Laboratory, the University of New Mexico and the University of Illinois at Urbana-Champaign.
Leveraging Sunlight For Fuel Production
The last couple of times CleanTechnica covered the artificial leaf concept, the end goal was to use solar energy for splitting water, arriving at hydrogen as the end product. Essentially, it’s a hydrogen-based energy storage system.
It’s worth pausing to note that one of the original pioneers of the artificial leaf concept, Daniel Nocera, has also been making waves in energy storage. The flow battery work of his startup Sun Catalytix caught the attention of Lockheed Martin back in 2012. Lockheed eventually acquired the company in 2014 and renamed the operation “Lockheed Martin Advanced Energy Storage, LLC.”
Meanwhile, artificial leaf research has been progressing on other fronts. Last year, for example, a team at Harvard came up with a “bionic leaf” system that produces rubbing alcohol.
The new UIC/Argonne iteration takes it up to the next level. The new system produces a mix of carbon and hydrogen that could be used directly as synthetic gas, which doesn’t seem like that big of a deal except when you consider the atmospheric carbon capture angle.
Once you have syngas, you can also get to diesel, gasoline and other liquid fuels. Here’s how the UIC team articulates it:
The ability to turn CO2 into fuel at a cost comparable to a gallon of gasoline would render fossil fuels obsolete.
The Argonne team is particularly excited about tackling the carbon monoxide conversion part of the process, because in CO2 form carbon is difficult to recombine with for anything else.
That’s the sticky wicket in a nutshell — finding an efficient, commercially viable way to convert CO2 to CO.
A One-Pot Carbon Upcycling System
Plants and other organisms can hack CO2 into CO without batting an eyelash, but replicating that process in the lab during one human lifetime is quite a tall order.
The basic idea behind the new artificial leaf is an economical one-pot system that encompasses the entire three-step process.
The first two steps sound a lot like conventional artificial leaf business. Step one is the energy harvesting part, in which photons are converted into pairs of electrons (negative charges) and “holes” (positive charges).
Step two is the reaction between holes and water molecules. That results in the creation of protons and oxygen molecules.
Step three is where the magic happens:
Finally, the protons, electrons and carbon dioxide all react together to create carbon monoxide and water.
To flesh out that third step, you can read all about the new system in the journal Science under the title “Nanostructured transition metal dichalcogenide electrocatalysts for CO2 reduction in ionic liquid.”
For those of you on the go, the short version is that the research team was challenged to come up with a durable, economical catalyst to accomplish the reaction in Step 3.
They finally settled on using nanoscale flakes of the transition metal WSe2 (tungsten diselenide). In addition, the team found that adding an ionic (“salty”) liquid to water further enhanced the efficiency. Here’s the rundown from UIC:
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.
As for commercialization, if that doesn’t work out on Earth then there’s always Mars, which has atmospherice CO2 in abundance.
Just add water…
Photo (cropped): “Simulated sunlight powers a solar cell that converts atmospheric carbon dioxide directly into syngas” via UIC.