Scientists have co-created a system that harnesses solar energy to split water molecules and hydrogen-eating bacteria to produce liquid fuels, at a rate considerably better than natural photosynthesis.
Created by 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, the system, named bionic leaf 2.0, builds on previous work by Nocera, Silver and others, which was capable of creating solvent isopropanol with solar energy, but was limited in a number of areas.
Primarily, the previous attempt was challenged by the fact that the catalyst being used to produce hydrogen also created reactive oxygen species, a form of molecule that would attack and destroy the bacterial DNA inherent to the system.
In order to overcome this challenge, the team were forced to run the system at voltages that reduced efficiency. For 2.0, they have now developed a new catalyst, comprised of a cobalt-phosphorous alloy, that doesn’t make the reactive oxygen species that hindered their previous efforts.
The increase in efficiency is dramatic. The fastest growing plants convert solar energy into biomass at a 1% rate of efficiency. Bionic leaf 2.0, however, achieves the same process, and more, with 10% efficiency.
“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,” said Nocera.
The potential of the system is huge. Even it just its second iteration, its portfolio has been expanded to include isobutanol, isopentanol and PHB, a bio-plastic precursor.
Additionally, the new catalyst’s chemical design comes with the bonus of the system being able to “self-heal”, meaning that there is no risk of material leeching into solution.
As pointed out by Silver, the genius of this system is that, “these catalysts are totally biologically compatible.”
There may be the chance of even greater increases in efficiency in the future but, for now, Nocera considers the system efficient enough to consider commercial applications and, in conjunction with Harvard’s First 100 Watts program, is looking to continue developing the technology and its applications in nations such as India.
Nocera has said that the new system is in many ways the fulfilment of the initial promise of his “artificial leaf”, a project that used solar power to split water to make hydrogen fuel. The versatility of the new system, however, far exceeds the original.
“The beauty of biology is it’s the world’s greatest chemist – biology can do chemistry we can’t do easily,” Silver said.
“In principle, we have a platform that can make any downstream carbon-based molecule. So this has the potential to be incredibly versatile.”