Building a Bionic Leaf

Building a Bionic Leaf

A collaboration between scientists at Harvard University and the Wyss Institute for Biologically Inspired Engineering claims to have developed a bionic leaf. Using bacterium the artificial vegetation is turning sunlight into liquid fuel. Once the bionic leaf splits water into hydrogen and oxygen the soil bacterium Ralstonia eutropha consumes the hydrogen gas converting it into protons and electrons. Protons and electrons are integrated into carbon dioxide molecules and used for reproduction by the bacterium.

Ralstonia eutropha, pictured here, makes fuel using the hydrogen produced via catalysts powered by electric current from a photovoltaic panel.

Ralstonia eutropha, pictured here, makes fuel using the hydrogen produced via catalysts powered by electric current from a photovoltaic panel.

This synthesis of technology and biology is effectively a bioreactor which feeds microbes with hydrogen from water split by special catalysts connected in a circuit with photovoltaics. This combination is theoretically more effective at turning sunlight into fuel than either solely biological or technological systems. Daniel Nocera, now of Harvard University, began experimenting with cheap, water splitting catalysts in 2009. He was able to produce hydrogen from water using his cobalt–phosphate catalysts, but hydrogen never caught on as an alternative fuel. So when he arrived at Harvard he began working with biochemist Pamela Silver of Harvard Medical School to build a hybrid system that could make a more useful fuel.

Once they combined the electrical components with the bacterium they were able to synthesize the optimal features of both. Photovoltaic cells are more efficient at turning sunlight into energy than regular photosynthesis and the new catalysts are able to split ordinary water, from practically any source, even the most impacted of waterbodies. And microbes are highly efficient at turning incoming energy into fuel, food and pharmaceuticals. So Nocera, Torella and the rest of the team joined the photovoltaic water-splitting wafer with Ralstonia eutropha, a soil bacteria that can use the split hydrogen to power the building of molecules out of carbon, in a jar.

Using a variant of R. eutropha the team created isopropanol (C3H8O), an alcohol molecule which can be used as fuel similarly to ethanol, and can easily be separated from water with salt. Their bionic leaf can produce 216 milligrams of isopropanol per liter of water. This is not the first time this bacterium, or any bacteria, has been used to attempt to make fuel from solar electricity, however the Harvard team is the first to put the tweaked microbe in the same chamber as the water-splitting mechanism. Previous attempts kept the living and non-living components separate in order to keep the abiotic chemistry from killing the biologicals. This new work re-energizes the field of electrofuel production and makes reverse combustion, the process of using fossil fuel waste, carbon dioxide, to produce clean energy, seem possible on a grander scale.

The full study was published in February in the Proceedings of the National Academy of Sciences and can be viewed here: http://www.pnas.org/content/early/2015/02/06/1424872112.