Bionic leaf 2.0 turns sunlight into liquid fuel
In 2015, a team of researchers at Harvard University in the US had successfully used bacteria to convert solar energy and carbon dioxide (CO2) into liquid isopropanol with an artificial "bionic" leaf. Now with a new system, Bionic leaf 2.0 surpasses the efficiency of photosynthesis. By a factor ten.
Daniel Nocera, the Patterson Rockwood Professor of Energy at Harvard University, and Pamela Silver, the Elliott T. and Onie H. Adams Professor of Biochemistry and Systems Biology at Harvard Medical School, have co-created a system that uses solar energy to split water molecules and hydrogen-eating bacteria to produce liquid fuels.
The paper “Water splitting–biosynthetic system with CO2reduction efficiencies exceeding photosynthesis” whose lead authors include postdoctoral fellow Chong Liu and graduate student Brendan Colón has recently been published in Science.
– This is a true artificial photosynthesis system. 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, Nocera said.
Bionic leaf 2.0
While the study shows the system can be used to generate usable fuels, its potential doesn’t end there, said Silver, who is also a founding core member of the Wyss Institute at Harvard University.
– The beauty of biology is it’s the world’s greatest chemist — biology can do chemistry we can’t do easily. In principle, we have a platform that can make any downstream carbon-based molecule. So this has the potential to be incredibly versatile, she said.
Dubbed “bionic leaf 2.0,” the new 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, molecules that 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.
From 1 to 10 percent efficiency
– For this paper, we designed a new cobalt-phosphorous 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 explained.
The system can now convert solar energy to biomass with 10 percent efficiency, Nocera said, far above the 1 percent seen in the fastest-growing plants.
In addition to increasing the efficiency, Nocera and colleagues 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, a process first demonstrated by Professor Anthony Sinskey of MIT.
The new catalyst also came with another advantage — its chemical design allows it to “self-heal,” meaning it wouldn’t leach material into solution.
– This is the genius of Dan, these catalysts are totally biologically compatible, Silver said.
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. But I also want to bring this technology to the developing world as well, Nocera said.
Working in conjunction with the First 100 Watts programme 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.
In many ways, Nocera said, the new system marks the fulfillment of the promise of his “artificial leaf,” which used solar power to split water and make hydrogen fuel.
– If you think about it, photosynthesis is amazing. It takes sunlight, water, and air — and then look at a tree. That’s exactly what we did, but we do it significantly better, because we turn all that energy into a fuel, ended Nocera.