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Unexpected discovery leads to new strategy for carbon fixation

By Karen Graham     Aug 16, 2017 in Science
Scientists in Japan and China announced last week they had discovered an "unexpected" approach to the capture and storage of carbon dioxide away from the atmosphere while working toward the elusive lithium-air battery.
Demonstrating once again that scientific research can yield unexpected but ground-breaking results, the scientists came across the carbon-fixation strategy while trying to recharge a lithium-CO2 battery prototype.
The researchers published their new strategy for isolating solid carbon dust from gaseous carbon dioxide using a design intended for a lithium-CO2 battery in Joule, a new interdisciplinary energy journal from Cell Press on July 9, 2017.
A flowchart of energy storage and carbon fixation using Li-CO2 technology. 
Creative Commons Licens...
A flowchart of energy storage and carbon fixation using Li-CO2 technology. Creative Commons License: Attrition, no deriv.
Qiao et al.
Research has been ongoing in trying to find ways to convert harmful carbon dioxide emissions into other carbon-containing compounds because CO2 is a harmful greenhouse gas contributing to global warming. Several methods involve changing CO2 into more desirable products, like oxygen and sugar, or sequestration is used, a process involving the injection of CO2 into rock formations.
READ MORE: Turning air into water and CO2 into fuel — Two global challenges
"The problem with most physical and chemical pathways for CO2 fixation is that their products are gases and liquids that need to be further liquefied or compressed, and that inevitably leads to additional energy consumption and even more CO2 emissions," senior author Haoshen Zhou of Japan's National Institute of Advanced Industrial Science and Technology and China's Nanjing University, said in a statement.
The unexpected discovery
While working on recharging a lithium-CO2 battery prototype, the researchers found that instead of fully regenerating lithium ions and CO2 from the lithium carbonate and carbon produced during battery discharge, as would happen with a reversible Li-CO2 battery, the lithium carbonate decomposed, leaving additional CO2 and gaseous oxygen that couldn't be captured because of the speed of the reaction.
Usually, the kind of reaction observed would cause physical degradation and reduced functional lifespan for a battery, but the creation of a solid carbon component revealed an unexpected advantage in that this could be a method of fixing carbon in a stable and easy-to-dispose-of form.
Diagram showing an energy storage system and the CO2 fixation strategy.
Creative Commons License: A...
Diagram showing an energy storage system and the CO2 fixation strategy. Creative Commons License: Apprition, no deriv.
Qiao et al.
"What is impressive about this work is the possibility to convert one-third of the CO2 species to carbon with a high theoretical energy efficiency above 70%," says Joule scientific editor Rahul Malik, reports Phys.Org. "Battery architecture is an unforeseen but intriguing way to look at carbon fixation."
Zhou points out there is a remaining challenge for both carbon fixation and battery performance - and that is moving from pure CO2 to ambient air, a jump that would potentially allow for treating atmospheric CO2 in the first case, and would advance towards the theoretically powerful but not-yet-stable lithium-air battery technology in the second case.
Zhou and his colleagues are very excited about their system's potential, hopeful it will lead to converting carbon dioxide into pure carbon and oxygen gas. "Attaining the release of oxygen gas upon charging, coupled with the accumulation of solid carbon, would realize an electrochemical carbon dioxide fixation strategy analogous to photosynthesis," says Zhou.
More about carbonfixation, LiCO2 battery, Carbon dioxide, Greenhouse Gas, Technology