Researchers design bionic leaf capable of converting sunlight into liquid fuel

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Artificial leaf created waves in the world of biology and renewable energy the moment it was announced by Daniel Nocera back in 2011 and his latest research involves utilising hydrogen from this artificial leaf, carbon dioxide from another source and feeding it to bacterium Ralstonia eutropha to create liquid fuel.

The research is a collaboration between scientists from Harvard University’s Faculty of Arts and Sciences, Harvard Medical School and the Wyss Institute for Biologically Inspired Engineering at Harvard University findings of which are published on February 9 in PNAS.

The artificial leaf is more of an idea rather than being an actual leaf and using it Nocera harnessed sunlight with silicon to split water into oxygen and hydrogen. The main objective was to utilise this hydrogen for hydrogen fuel cells, but as hydrogen has failed to catch on as a practical fuel for cars or for power generation scientists have now created a system that uses bacteria to convert solar energy into a liquid fuel using this leaf.

The new system involves using the “artificial leaf” to split water into hydrogen and oxygen; carbon dioxide from another source and a bacterium engineered to convert carbon dioxide plus hydrogen into the liquid fuel isopropanol.

“This is a proof of concept that you can have a way of harvesting solar energy and storing it in the form of a liquid fuel,” said Pamela Silver, who is a founding core faculty member of the Wyss. “Dan’s formidable discovery of the catalyst really set this off, and we had a mission of wanting to interface some kinds of organisms with the harvesting of solar energy. It was a perfect match.”

Dubbed as a bionic leaf, the new system is based around the idea of developing a system that is readily accessible and inexpensive and is made from readily available material.

In the system, once the artificial leaf produces oxygen and hydrogen, the hydrogen is fed to a bacterium called Ralstonia eutropha. An enzyme takes the hydrogen back to protons and electrons, then combines them with carbon dioxide to replicate—making more cells.

Next, based on discoveries made earlier by Anthony Sinskey, professor of microbiology and of health sciences and technology at MIT, new pathways in the bacterium are metabolically engineered to make isopropanol.

As for the challenges, the team is looking to increase their system’s ability to translate solar energy to biomass by optimizing the catalyst and the bacteria. As it stands, the bionic leaf has an efficiency of 1 per cent rate of converting sunlight into isopropanol. The scientists are looking to reach a 5 per cent efficiency. Nature’s rate of efficiency for photosynthesis of turning sunlight into biomass is also 1 per cent.

“We’re almost at a 1 percent efficiency rate of converting sunlight into isopropanol,” Nocera said. “There have been 2.6 billion years of evolution, and Pam and I working together a year and a half have already achieved the efficiency of photosynthesis.”

However, not everyone is convinced that this approach makes much sense. Stephen Mayfield, director of the California Center for Algae Biotechnology, believes that this is a “solution looking for a problem.”

Mayfield told CBS News that the exact same thing – turning electrons into biomass – has already been done many a times previously by using the same bacteria.

“Our problem is not that we have too much H2 and O2 sitting around generated by PV cells that we need to convert it to liquid fuels. Our problem is that fossil fuels were cheap so we burned a boat load of them and now we have problems with our climate”, Mayfield said.

“It’s not that I don’t believe. It’s that damn math thing. It just never works out.”