Sustainable and Renewable Carbon and Nitrogen Cycles for Fuel and Crop Production
Daniel Nocera a
a Harvard University, 12 Oxford Street, Cambridge, 0, United States
nanoGe Fall Meeting
Proceedings of nanoGe Fall Meeting19 (NGFM19)
#SolFuel19. Solar Fuel Synthesis: From Bio-inspired Catalysis to Devices
Berlin, Germany, 2019 November 3rd - 8th
Organizers: Mahshid Ahmadi, Efrat Lifshitz, Cristiane Morais Smith, Marcus Scheele, Roel van de Krol, Pablo P. Boix, Erwin Reisner, Stefan Weber, Germà Garcia-Belmonte, Doron Naveh and Maksym Yarema
Keynote, Daniel Nocera, presentation 293
Publication date: 16th July 2019

Hybrid biological | inorganic (HBI) constructs have been created to use sunlight, air and water (as the only starting materials) to accomplish carbon and nitrogen fixation, thus providing a path to a sustainable nitrogen and carbon cycle for distributed and renewable fuels and crop production.

The carbon and nitrogen fixation cycles begin with the artificial leaf, which was invented to accomplish the solar process of natural photosynthesis – the splitting of water to hydrogen and oxygen using sunlight – under ambient conditions. To create the artificial leaf, an oxygen evolving complex of Photosystem II was mimicked, the most important property of which was the self-healing nature of the catalyst. Self-healing catalysts of the artificial leaf permit water splitting to be accomplished under benign conditions and thus the system may be easily interfaced with bioorganisms. To this end, using the tools of synthetic biology, a bio-engineered bacterium converts carbon dioxide from air, along with the hydrogen produced from the catalysts of the artificial leaf, into biomass and liquid fuels, thus closing an entire artificial photosynthetic cycle. The HBI, called the Bionic Leaf, operates at unprecedented solar-to-biomass (10.7%) and solar-to-liquid fuels (6.2%) efficiencies, greatly exceeding the 1% efficiency of natural photosynthesis.

Extending this approach, we have discovered a renewable and distributed synthesis of ammonia (and fertilizer) at ambient conditions by coupling solar-based water splitting to a nitrogen fixing bioorganism in a single reactor. Nitrogen is fixed to ammonia by using the hydrogen produced from water splitting to power a nitrogenase installed in a bioorganism. Nitrogen reduction reaction proceeds at a turnover number of 1010 per cell and operates without the need for a carbon feedstock (other than the CO2 provided from air). This nitrogen fixing HBI can be powered by distributed renewable electricity, enabling sustainable crop production with a large and negative carbon budget.

The science that will be presented will show that using only sunlight, air and water, distributed and renewable systems may be designed to produce fuel (carbon neutral) and food (carbon negative) within sustainable cycles for the biogenic elements.

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