United States. An international team of scientists led by Liang-shi Li at Indiana University has achieved a new milestone in the quest to recycle carbon dioxide in the earth's atmosphere and turn it into carbon-neutral fuels and other materials.
Chemists have designed a molecule that uses light or electricity to convert carbon dioxide from greenhouse gases into carbon monoxide — a carbon-neutral fuel source — more efficiently than any other "carbon reduction" method.
"If you can create a molecule that is efficient enough for this reaction, you will produce energy that is free and storable in the form of fuels," said Li, an associate professor at the IU Bloomington College of Arts and Sciences Department of Chemistry. "This study is a big leap in that direction."
Burnt fuel – like carbon monoxide – produces carbon dioxide and releases energy. Converting carbon dioxide back into fuel requires at least the same amount of energy. An important goal among scientists has been to decrease the excess energy needed.
This is exactly what the Li molecule achieves: requiring the least amount of energy reported so far to drive the formation of carbon monoxide. The molecule — a nanographene-rhenium complex connected through an organic compound known as bipyridine — triggers a highly efficient reaction that converts carbon dioxide into carbon monoxide.
The ability to efficiently and uniquely create carbon monoxide is important because of the versatility of the molecule.
"Carbon monoxide is an important raw material in many industrial processes," Li said. "It's also a way to store energy as a carbon-neutral fuel, as it's not returning more carbon to the atmosphere than it has already removed. It's just relaunching the solar energy it used to make it."
The secret to the molecule's efficiency is nanographene — a nanoscale piece of graphite, a common form of carbon — because the material's dark color absorbs a lot of sunlight.
Li said bipyridine metal complexes have long been studied to reduce carbon dioxide to carbon monoxide with sunlight. But these molecules can use only a small portion of the light in sunlight, mainly in the ultraviolet range, which is invisible to the naked eye. In contrast, the molecule developed at IU harnesses the light-absorbing power of nanographene to create a reaction that uses sunlight at the wavelength of up to 600 nanometers, a large part of the visible light spectrum.
Essentially, Li said, the molecule acts as a two-part system: an "energy-collecting" nanographene that absorbs energy from sunlight and an atomic rhenium "engine" that produces carbon monoxide. The energy collector drives a flow of electrons to the rhenium atom, which repeatedly binds and converts normally stable carbon dioxide into carbon monoxide.
Subsequently, Li plans to make the molecule more potent, including making it last longer and survive in non-liquid form, since solid catalysts are easier to use in the real world. It is also working to replace the rhenium atom in the molecule — a rare element — with manganese, a more common and less expensive metal.
Source: Indiana University Bloomington.
