Plants have been transforming sunlight into things that we can use for fuel for 1.6 billion years. However, with a few exceptions, they are still only about 1% efficient.
In 2009, Daniel D. Nocera, the Henry Dreyfus Professor of Energy at the Massachusetts Institute of Technology (MIT) founded a startup called Sun Catalytix to develop a prototype design for a system to convert sunlight into storable hydrogen which could be used to produce electricity.
During the next two years, Nocera developed what he called the “artificial leaf,” a silicon strip coated with catalysts on each side. When placed in water and exposed to sunlight, the leaf splits the H2O to release oxygen on one side and hydrogen on the other.
In August 2014, Lockheed Martin purchased the assets of Sun Catalytix, and now Sun Catalytix technology is being commercialized under the venture, Lockheed Martin GridStar Flow.
Soon after, Nocera was appointed Patterson Rockwood Professor of Energy in the Department of Chemistry and Chemical Biology at Harvard University, teaming up with Pamela Silver of Harvard Medical School to create the “Bionic Leaf”.
This merged the artificial leaf with genetically engineered bacteria Ralstonia eutropha that feed on the hydrogen and convert CO₂ in the air into alcohol fuels or chemicals.
The first model that used the nickel-molybdenum-zinc alloy created a reactive oxygen species that destroyed the bacteria’s DNA.
Abnormally high voltages were used to prevent the microbes from dying, but they also resulted in reduced efficiency. An improved model removed the nickel-molybdenum-zinc alloy catalyst and allowed the team to reduce the voltage.
The new catalyst improved the efficiency of producing alcohol fuels by nearly 10%. The Bionic Leaf operates at solar-to-biomass and solar-to-liquid fuels efficiencies that greatly exceed the highest solar-to-biomass efficiencies of natural photosynthesis.
With this system, Xanthobacter bacteria which pull nitrogen from the air and use the bioplastic, which is basically stored hydrogen, to drive the fixation cycle to make a bacteria-laden yellowish liquid that can be sprayed onto fields.
But the real proof is in the radishes. In greenhouse experiments at the Arnold Arboretum, radishes grown with this X. autotrophicus fertilizer ended up more than double the size of control radishes grown without added fertilizer.
The researchers have used their approach to grow five crop cycles. The vegetables receiving the bionic-leaf-derived fertilizer weigh 150% more than the control crops. In 2018, Nocera founded a second company called Kula Bio, to focus on the development of renewable and distributed crop organic fertilization and land restoration.
When mass-produced, these tiny solar “carbon-negative” fuel factories could be inexpensive enough for everyday people to use to power their vehicles and run their lights and appliances.
Farmers with a small on-site array of bionic leaves could create enough fertilizer for their own needs instead of buying container-loads of synthetic fertilizer produced at sprawling CO₂-spewing factories and shipped for thousands of miles.
Daniel D Nocera and Dilek K Dogutan,“Artificial Photosynthesis at Efficiencies Greatly Exceeding That of Natural Photosynthesis” Accounts of Chemical Research 52(11) · October 2019.
Discover solution 44: soybean automobiles
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