Plasma-Activated Mist: Continuous-Flow, Scalable Nitrogen Fixation, and Aeroponics
Haotian Gao, Guoli Wang, Zhongzheng Huang, Lanlan Nie, Dawei Liu, Xinpei Lu, Guangyuan He, Kostya Ostrikov
Abstract
Nitrogen fixation underpins diverse biological and industrial processes and is currently one of the leading producers of carbon emissions at a global scale. Radical solutions to decarbonize nitrogen fixation include plasma-electrified ammonia (NH 3 ) synthesis using water and atmospheric nitrogen. Here, we resolve the intrinsic limitations of the state-of-the-art solutions in (i) energy efficiency; (ii) scalability; (iii) direct use of clean renewable energy; and (iv) direct sustainable application of water-based nitrogen fixation by the novel, scalable plasma-enabled process and system for the continuous-flow, scalable nitrogen fixation, and aeroponics using plasma-activated mist (PAM). The new approach is based on the continuous, scalable, in-flow generation of PAM containing NH 4 +, NO 3 –, NO 2 –, and other nitrogen-fixation species through the reaction of large-area uniform air plasma and high-flux water mist containing large area-to-volume ratio micron-sized droplets. Through the solar-energy-driven plasma-assisted oxidation confined within the droplet micro-reactors, a liquid-phase nitrogen fixation product dominated by NO 3 – is produced. This PAM nitrogen fixation system is applied for the continuous delivery of nitrogen-based nutrients directly to the roots of living plants using a custom-designed aeroponic system which increases the leaf emergence rate and leaf area of bean sprouts by more than 30%. The unique energy concentration in droplet microreactors leads to the much increased (from 2 to 39 times) energy efficiency at a larger scale compared to the key types of common lab-scale plasma reactors. Compatibility with direct solar power, flow-reactor chemistry, and electrified processes at industry-relevant scales make this low-cost, low-carbon-footprint, renewable-energy-driven process and system promising for the widespread sustainable and distributed production and applications of plasma-enabled nitrogen fixation.