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catalysts, pairing them with an unconven-
tional ionic liquid as the electrolyte inside a
two-compartment, three-electrode electro-
chemical 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 cata-
lysts 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 break-
through, he said, was to use an ionic fluid
called ethyl-methyl-imidazolium tetra-
fluoroborate, mixed 50-50 with water.
¡°The combination of water and the ionic liquid makes a co-catalyst that pre-
serves the catalyst¡¯s active sites under the harsh reduction reaction condi-
tions,¡± 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 mon-
oxide 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. (continued pg 3)
Game-Changing Photosynthetic Solar Cell Engineered
¡®Artificial leaf¡¯ converts atmospheric CO2 directly into syngas
LDN an alternative
therapy... Pg 9
An historic plane
trip... Pg 3
2nd Annual Moose
Festival... Pg 13
An evening with
Joe Walsh... Pg 14
Breakthrough solar cell captures CO2
and sunlight, produces burnable fuel
Bill Burton, July 28, 2016: Researchers at the
University of Illinois at Chicago have engi-
neered a potentially game-changing solar cell
that cheaply and efficiently converts atmo-
spheric carbon dioxide directly into usable hy-
drocarbon fuel, using only sunlight for energy.
The finding is reported in the July 29 issue of
Science and was funded by the National Sci-
ence 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 atmo-
spheric 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.
2016 AUG/SEP #7-4
¡°The new solar cell is not photovoltaic - it is 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 fos-
sil 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 hydro-
carbon 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. Engi-
neers 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 prop-
erties,¡± he said.
Salehi-Khojin and his coworkers focused on a family of nano-structured
compounds called transition metal dichalcogenides - or TMDCs - as
Simulated sunlight powers a solar cell that converts
atmospheric carbon dioxide directly into syngas.
Image: news.uic.edu