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New “Artificial Photosynthesis” System Produces Methane With 10x Efficiency

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A study from six chemists at the University of Chicago shows an innovative new system for artificial photosynthesis that is more productive than previous artificial systems by an order of magnitude. Above, an artistic illustration of the process. Credit: Illustration by Peter Allen

University of Chicago breakthrough creates methane fuel from sun, carbon dioxide, and water.

Humans have relied on fossil fuels for concentrated energy for the past two centuries. Our society has been taking advantage of the convenient, energy-dense substances packed with the proceeds from hundreds of millions of years of <span class="glossaryLink" aria-describedby="tt" data-cmtooltip="

Photosynthesis is how plants and some microorganisms use sunlight to synthesize carbohydrates from carbon dioxide and water.

” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>photosynthesis. However, that supply is finite, and fossil fuel consumption has an enormous negative impact on Earth’s climate.

“The biggest challenge many people don’t realize is that even nature has no solution for the amount of energy we use,” said <span class="glossaryLink" aria-describedby="tt" data-cmtooltip="

University of Chicago
Founded in 1890, the University of Chicago (UChicago, U of C, or Chicago) is a private research university in Chicago, Illinois. Located on a 217-acre campus in Chicago's Hyde Park neighborhood, near Lake Michigan, the school holds top-ten positions in various national and international rankings. UChicago is also well known for its professional schools: Pritzker School of Medicine, Booth School of Business, Law School, School of Social Service Administration, Harris School of Public Policy Studies, Divinity School and the Graham School of Continuing Liberal and Professional Studies, and Pritzker School of Molecular Engineering.

” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>University of Chicago chemist Wenbin Lin. Not even photosynthesis is that good, he said: “We will have to do better than nature, and that’s scary.”

“Artificial photosynthesis” is one possible option scientists are exploring. This entails reworking a plant’s system to make our own kinds of fuels. However, the chemical equipment in a single leaf is incredibly complex, and not so easy to turn to our own purposes.

Now, an innovative new system for artificial photosynthesis that is more productive than previous artificial systems by an order of magnitude is presented in a study published in the journal Nature Catalysis on November 10 by six chemists at the University of Chicago. Unlike regular photosynthesis, which produces carbohydrates from carbon dioxide and water, artificial photosynthesis could produce ethanol, methane, or other fuels.

Although it still has a long way to go before it can become a way for you to fuel your car every day, the method gives scientists a new direction to explore. Plus, in the shorter term, it may be useful for the production of other chemicals.

“This is a huge improvement on existing systems, but just as importantly, we were able to lay out a very clear understanding of how this artificial system works at the molecular level, which has not been accomplished before,” said Lin, who is the James Franck Professor of Chemistry at the University of Chicago and senior author of the study.

‘We will need something else’

“Without natural photosynthesis, we would not be here. It made the oxygen we breathe on Earth and it makes the food we eat,” said Lin. “But it will never be efficient enough to supply fuel for us to drive cars; so we will need something else.”

The trouble is that photosynthesis is built to create carbohydrates, which are great for fueling us, but not our cars, which need much more concentrated energy. So researchers looking to create alternates to fossil fuels have to re-engineer the process to create more energy-dense fuels, such as ethanol or methane.

In nature, photosynthesis is performed by several very complex assemblies of proteins and pigments. They take in water and carbon dioxide, break the molecules apart, and rearrange the atoms to make carbohydrates—a long string of hydrogen-oxygen-carbon compounds. Scientists, however, need to rework the reactions to instead produce a different arrangement with just hydrogen surrounding a juicy carbon core—CH4, also known as methane.

This re-engineering is much trickier than it sounds; people have been tinkering with it for decades, trying to get closer to the efficiency of nature.

Lin and his lab team thought that they might try adding something that artificial photosynthesis systems to date haven’t included: <span class="glossaryLink" aria-describedby="tt" data-cmtooltip="

amino acids
<div class="cell text-container large-6 small-order-0 large-order-1"> <div class="text-wrapper"><br />Amino acids are a set of organic compounds used to build proteins. There are about 500 naturally occurring known amino acids, though only 20 appear in the genetic code. Proteins consist of one or more chains of amino acids called polypeptides. The sequence of the amino acid chain causes the polypeptide to fold into a shape that is biologically active. The amino acid sequences of proteins are encoded in the genes. Nine proteinogenic amino acids are called "essential" for humans because they cannot be produced from other compounds by the human body and so must be taken in as food.<br /></div> </div>

” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>amino acids.

The team started with a type of material called a metal-organic framework or MOF, a class of compounds made up of metal ions held together by an organic linking molecules. Then they designed the <span class="glossaryLink" aria-describedby="tt" data-cmtooltip="

Metal–organic frameworks (MOFs) are a new class of porous material compounds consisting of metal-to-organic ligand interactions. MOFs show promise to improve the efficiency and effectiveness of practical gas separation systems and are of interest for the storage of gases such as hydrogen and carbon dioxide.

” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>MOFs as a single layer, in order to provide the maximum surface area for chemical reactions, and submerged everything in a solution that included a cobalt compound to ferry electrons around. Finally, they added amino acids to the MOFs, and experimented to find out which worked best.

“The biggest challenge many people don’t realize is that even nature has no solution for the amount of energy we use.”

Prof. Wenbin Lin

They were able to make improvements to both halves of the reaction: the process that breaks apart water and the one that adds electrons and protons to carbon dioxide. In both cases, the amino acids helped the reaction go more efficiently.

Even with the significantly improved performance, however, artificial photosynthesis has a long way to go before it can produce enough fuel to be relevant for widespread use. “Where we are now, it would need to scale up by many orders of magnitude to make an sufficient amount of methane for our consumption,” Lin said.

The breakthrough could also be applied widely to other chemical reactions; you need to make a lot of fuel for it to have an impact, but much smaller quantities of some molecules, such as the starting materials to make pharmaceutical drugs and nylons, among others, could be very useful.

“So many of these fundamental processes are the same,” said Lin. “If you develop good chemistries, they can be plugged into many systems.”

The scientists used resources at the Advanced Photon Source, a synchrotron located at the U.S. Department of Energy’s Argonne National Laboratory, to characterize the materials.

The co-first authors of the paper were Guangxu Lan (PhD’20, now with Peking University), graduate student Yingjie Fan, and Wenjie Shi (Visiting student, now with Tianjin University of Technology. The other authors of the paper were Eric You (BS’20, now a graduate student at <span class="glossaryLink" aria-describedby="tt" data-cmtooltip="

MIT is an acronym for the Massachusetts Institute of Technology. It is a prestigious private research university in Cambridge, Massachusetts that was founded in 1861. It is organized into five Schools: architecture and planning; engineering; humanities, arts, and social sciences; management; and science. MIT's impact includes many scientific breakthroughs and technological advances. Their stated goal is to make a better world through education, research, and innovation.

” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>MIT) and Samuel Veroneau (BS’20, now a PhD student at Harvard University).

Reference: “Biomimetic active sites on monolayered metal–organic frameworks for artificial photosynthesis” by Guangxu Lan, Yingjie Fan, Wenjie Shi, Eric You, Samuel S. Veroneau and Wenbin Lin, 10 November 2022, Nature Catalysis.
DOI: 10.1038/s41929-022-00865-5

Funding: University of Chicago, National Science Foundation, China Scholarship Council

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