‘Bionic’ leaf converts light to fuel better than plants

08 Jun 2016

New photovoltaic and biochemical hybrid surpasses the natural efficiency of photosynthesis.

Daniel Nocera, the Patterson Rockwood Professor of Energy at Harvard University, Ma, USA, and Pamela Silver, the Elliott T. and Onie H. Adams Professor of Biochemistry and Systems Biology at Harvard Medical School, have co-developed a system that uses solar energy to split water molecules and hydrogen-eating bacteria to produce liquid fuels. Their work has just been published in Science, including work by postdoctoral fellow Chong Liu and graduate student Brendan Colón.

“This is a true artificial photosynthesis system,” Nocera commented. “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.”

While the study shows the system can be used to generate what the researchers are calling “usable fuels”, its potential doesn’t end there, said Silver, who is also a founding member of the Wyss Institute at Harvard University.

A cross-disciplinary team at Harvard has created a system that uses solar energy to split water molecules and hydrogen-eating bacteria to produce liquid fuels. The system can convert solar energy to biomass with 10% efficiency, far above the 1% observed in the fastest-growing plants.

’Bionic leaf 2.0’

Dubbed Bionic leaf 2.0, the system builds on previous work by Nocera, Silver, and others, which — though it was capable of using solar energy to make isopropanol — faced a number of challenges. Chief among those, Nocera said, was the fact that the catalyst used to produce hydrogen — a nickel-molybdenum-zinc alloy — also created reactive oxygen species, which attacked and destroyed the bacteria’s DNA. To avoid that, researchers were forced to run the system at abnormally high voltages, resulting in reduced efficiency.

“We have designed a new cobalt-phosphorous alloy catalyst, which we showed does not make reactive oxygen species,” said Nocera. “That allowed us to lower the voltage, and that led to a dramatic increase in efficiency.” The system can now convert solar energy to biomass with 10% efficiency, Nocera said, this is far above the 1% seen in the fastest-growing plants.

In addition to increasing the efficiency, Nocera’s team has expanded the portfolio of the system to include isobutanol and isopentanol. Researchers also used the system to create PHB, a bio-plastic precursor, a process first demonstrated by Professor Anthony Sinskey of MIT.

Though there may yet be room for additional increases in efficiency, Nocera said the system is already effective enough to consider possible commercial applications, but within a different model for technology translation. “It’s an important discovery — it says we can do better than photosynthesis,” Nocera said. “But I also want to bring this technology to the developing world as well.”

Working in conjunction with the “First 100 Watts” program at Harvard, which helped fund the research, Nocera hopes to continue developing the technology and its applications in nations like India with the help of their scientists.

Technical details

The Science paper abstract gives more technical information about how the artificial photosynthesis works: “When grown in contact with a biocompatible, Earth-abundant inorganic catalyst system, the bacterium Ralstonia eutropha consumed the produced hydrogen to synthesize biomass and fuels or chemical products from low CO₂ concentration in the presence of O₂.

“This scalable system has a CO₂ reduction energy efficiency of ~50% when producing bacterial biomass and liquid fuel alcohols, scrubbing 180g of CO₂ per kilowatt-hour of electricity. Coupling this hybrid device to existing photovoltaic systems would yield a CO₂ reduction energy efficiency of ~10%, exceeding that of natural photosynthetic systems.”

Video: Bionic Leaf Turns Sunlight Into Liquid Fuel