Hybrid inorganic | biological constructs have been created to use sunlight, air and water to accomplish carbon fixation and nitrogen fixation thus enabling distributed and renewable fuels and fertilizer generation. The carbon fixation cycle is achieved by interfacing the oxygen evolving and hydrogen evolving catalysts of the artificial leaf with an engineered bioorganism. Using the tools of synthetic biology, a bio-engineered bacterium has been developed to convert carbon dioxide, along with the hydrogen produced from the artificial leaf, into biomass and liquid fuels, thus closing an entire artificial photosynthetic cycle. This hybrid microbial | artificial leaf system scrubs 180 grams of CO2 from air, equivalent to 230,000 liters of air per 1 kWh of electricity. This hybrid device, called the bionic leaf, operates at unprecedented solar-to-biomass (10.7%) and solar-to-liquid fuels (6.2%) yields, greatly exceeding the 1% yield of natural photosynthesis. Extending our approach, we have discovered a renewable and distributed synthesis of ammonia 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 from the artificial leaf to power a nitrogenase installed in the bioorganism. The ammonia produced by the nitrogenase can be diverted from biomass formation to an extracellular product with the addition of an inhibitor. The nitrogen reduction reaction proceeds at a low \ driving force (~ 0.16 V) with a turnover number (TON) of 8 × 109 per cell and operates at 15 to 23% of the theoretical yield without the use of any sacrificial chemical reagents and carbon feedstock (which is provided by CO2 from air). This approach can be powered by distributed renewable electricity, enabling the sustainable production of nitrogen fertilizer.

Sustainable solar-to-fuels and solar-to-fertilizer production

253rd National Meeting (2017)

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