A 'bionic leaf' that turns sunlight into liquid fuel

Biologists have developed a way to make burnable liquid fuel out of sunlight, using an artificial leaf and a bucket of bacteria-infested water.

The invention could pave the way for numerous innovations—by converting solar power into biofuels, it may help solve the vexing difficulty of storing unused solar energy, which is one of the most common criticisms of solar power as a viable energy source.

The process could also help make plastics and other chemicals and substances useful to industry and research.

The current experiment builds on previous research led by Harvard engineer Daniel Nocera, who in 2011 demonstrated an "artificial leaf" device that uses solar power to generate usable energy.

Nocera's original invention was a wafer-like electrode suspended in water. When a current runs through the electrode from a power source such as a solar panel, for example, it causes the water to break down into its two components: hydrogen and oxygen.

Nocera's device garnered a lot of attention for opening up the possibility of using sunlight to create hydrogen fuel—once considered a possible alternative to gasoline.

But hydrogen has not taken off as a fuel source, even as other alternative energy sources survive and grow amid historically low oil prices. Hydrogen is expensive to transport, and the costs of adopting and distributing hydrogen are high. A gas station owner could more easily switch a pump from gasoline to biofuel, for example.

Now, Nocera and a team of Harvard researchers figured out how to use the bionic leaf to make a burnable biofuel, according to a study published Monday in the journal PNAS. The biologists on the team genetically modified a strain of bacteria that consumes hydrogen and produces isopropanol—the active ingredient in rubbing alcohol. In doing so, they essentially mimicked the natural process of photosynthesis—the way plants use energy from the sun to survive and grow.

This makes two things possible that have always been serious challenges for alternative energy space—solar energy can be converted into a storable form of energy, and the hydrogen can generate a more easily used fuel.

To be sure, the bionic leaf developments are highly unlikely to replace fossil fuels such as oil and natural gas any time soon—especially as the prices of both are currently so low. But it could be a good supplemental source.

Typically, people's energy needs are met by central energy production facilities—they get their electricity from the power grid, which is fed by coal- or gas-burning power plants, or solar farms, for example. Silver said locally produced energy could be feasible in developing countries that lack stable energy infrastructure, or could even appeal to people who choose to live off the grid.

"Instead of having to buy and store fuel, you can have your bucket of bacteria in your backyard," Silver said.