An international collaboration of researchers has demonstrated that solar -powered synthesis gas (syngas) could recycle carbon dioxide into fuels and useful chemicals, the results of which was published in the Proceedings of the National Academy of Science.
"If we can generate syngas from carbon dioxide utilizing only solar energy, we can use this as a precursor for methanol and other chemicals and fuels. This will significantly reduce overall CO2 emissions," said Zetian Mi, professor of electrical and computer engineering at the University of Michigan, who led the study and is a co-author on the paper.
Syngas is frequently derived from fossil fuels via electricity and is composed mainly of hydrogen and carbon monoxide with a little methane. Toxic chemicals are often added to make the process more efficient, which this new study demonstrates is not needed.
"Our new process is actually pretty simple, but it's exciting because it's not toxic, it's sustainable and it's very cost effective," said Roksana Rashid, who is a doctoral student in electrical and computer engineering at McGill University in Canada, and first author of the study.
The research group overcame the difficulty of splitting carbon dioxide molecules, thus creating a process that uses only solar energy. To achieve this, they interspersed an area of semiconductor nanowires with nanoparticles, the latter of which are made of gold coated with chromium oxide. These nanoparticles both attracted and eventually bent the carbon dioxide, ultimately weakening the bonds between the carbon and oxygen. The nanowires ultimately used light energy to split water molecules, separating the hydrogen from the oxygen. The metal catalysts then split the carbon dioxide, which produced carbon monoxide and often drawing in the free hydrogen to make methane.
Since the ratio of carbon monoxide to hydrogen affects the ease of producing a type of chemical or fuel, the important step in the process was changing the ratio of gold to chromium oxide in the nanoparticles. By doing this, the team was able to control the relative amounts of carbon monoxide and hydrogen produced in the reaction.
"What is surprising is the synergy between gold and chromium oxide to make the CO2 reduction to syngas efficient and tunable. That was not possible with a single metal catalyst," Mi said. "This opens up many exciting opportunities that were not previously considered."
The next goal for Mi is to increase the amount of light energy that is converted, which is currently a feeble 0.89%. He hopes that if the device can reach 10% of light energy conversion, he hopes the technology could be used for renewable energy, such as solar cells.
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