Major advance in artificial photosynthesis could turn carbon emissions into desirable chemicals

Researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley are reporting what could be a game changing innovation in energy and drastically reduce greenhouse gasses.

It is actually, simultaneously, a breakthrough in artificial photosynthesis as well as carbon capture and storage. The system described in the journal Nano Letters has the potential to not only reduce carbon emissions, but to turn carbon into a desirable commodity.

The system captures carbon dioxide emissions then uses solar energy and artificial photosynthesis to turn the carbon emissions, that would have gone into the atmosphere, into useful chemical products including liquid fuel, biodegradable plastic and even pharmaceutical drugs.

Just like plants use sunlight to turn carbon dioxide and water into carbohydrates, the new system would use carbon dioxide and water to make acetate, which can then be put to a wide variety of uses.

“We believe our system is a revolutionary leap forward in the field of artificial photosynthesis. Our system has the potential to fundamentally change the chemical and oil industry in that we can produce chemicals and fuels in a totally renewable way, rather than extracting them from deep below the ground,” said Peidong Yang a statement.

Yang is a chemist with Berkeley Lab’s Materials Sciences Division and one of the leaders of this study.

The problem, to date, with “carbon capture and storage” is storage. The carbon needs to be stored somewhere and that has the potential to create new environmental problems. By “storing” the carbon in useful products the technique has the potential to completely eliminate that problem and make carbon reduction profitable.

“In natural photosynthesis, leaves harvest solar energy and carbon dioxide is reduced and combined with water for the synthesis of molecular products that form biomass. In our system, nanowires harvest solar energy and deliver electrons to bacteria, where carbon dioxide is reduced and combined with water for the synthesis of a variety of targeted, value-added chemical products,” said Chris Chang of Berkeley Lab and UC Berkeley, an expert in catalysts for carbon-neutral energy conversions.

The system uses silicon and titanium oxide nanowire structures to create an “artificial forest”

“Our artificial forest is similar to the chloroplasts in green plants. When sunlight is absorbed, photo-excited electron−hole pairs are generated in the silicon and titanium oxide nanowires, which absorb different regions of the solar spectrum. The photo-generated electrons in the silicon will be passed onto bacteria for the CO2 reduction while the photo-generated holes in the titanium oxide split water molecules to make oxygen,” said Yang.

The forest is then populated with microbes that catalyze the carbon dioxide reduction. For the study, the team used the anaerobic bacterium Sporomusa ovata which takes electrons from its environment and uses them to reduce carbon dioxide.

“S. ovata is a great carbon dioxide catalyst as it makes acetate, a versatile chemical intermediate that can be used to manufacture a diverse array of useful chemicals. We were able to uniformly populate our nanowire array with S. ovata using buffered brackish water with trace vitamins as the only organic component,” aid Michelle Chang, an expert in biosynthesis.

Once the carbon dioxide is reduced, genetically engineered E.coli take over and synthesize the desired chemical products. According to the researchers the S. ovata and E.coli steps could potentially be combined in the future.

While this is, potentially, a remarkable and timely breakthrough the technology is not quite ready yet.

“We are currently working on our second generation system which has a solar-to-chemical conversion efficiency of three-percent. Once we can reach a conversion efficiency of 10-percent in a cost effective manner, the technology should be commercially viable,” said Yang.



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