New bionic leaf turns sunlight into liquid fuel

Scientists have developed a bionic leaf that uses solar energy to split water molecules and hydrogen-eating bacteria to produce liquid fuels, that surpasses the efficiency of photosynthesis seen in fastest growing plants.
"Before, people were using artificial photosynthesis for water-splitting, but this is a true A-to-Z system, and we've gone well over the efficiency of photosynthesis in nature," said Daniel Nocera, professor at Harvard University in the US.
While the study shows the system can be used to generate usable fuels, its potential does not end there, said Pamela Silver, professor at Harvard Medical School.
Dubbed "bionic leaf 2.0," the new system builds on previous work by Nocera, Silver and colleagues which - though it was capable of using solar energy to make isopropanol - faced a number of challenges.

Chief among those challenges was the fact that the catalyst used to produce hydrogen - a nickel-molybdenum-zinc alloy - also created reactive oxygen species, molecules that attacked and destroyed the bacteria's DNA, researchers said.
To avoid that problem, researchers were forced to run the system at abnormally high voltages, resulting in reduced efficiency.

"We designed a new cobalt-phosphorus alloy catalyst, which we showed does not make reactive oxygen species. That allowed us to lower the voltage, and that led to a dramatic increase in efficiency," Nocera said.
The system can now convert solar energy to biomass with 10 per cent efficiency, Nocera said, far above the one per cent seen in the fastest growing plants.

In addition to increasing the efficiency, researchers were able to expand the portfolio of the system to include isobutanol and isopentanol. Researchers also used the system to create PHB, a bio-plastic precursor.
The new catalyst also came with another advantage - its chemical design allows it to "self-heal" - meaning it wouldn't leech material into solution.
Though there may yet be room for additional increases in efficiency, Nocera said the system is already effective enough to consider possible commercial applications.
The research was published in the journal Science.