ECLIPSE: Mechanistic understanding and control of nitrogen activation in an atmospheric-pressure plasma-liquid process

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To reduce our reliance on fossil fuels, sustainable approaches are needed for activating and chemically transforming readily available feedstocks such as nitrogen from the air and water. Plasmas allow chemical reactions to be performed at atmospheric pressure and near room temperature without any catalyst using renewable electricity. Plasmas in contact with liquids have recently emerged as a new approach to promoting electrochemical reactions. However, chemical reactions taking place at a plasma-liquid interface are extremely complex and methods of probing the chemistry and gaining mechanistic insights are needed. This research program will develop cutting edge spectroscopic methods to study chemical reactions and species composition at the plasma-liquid interface under operating conditions. While the methods are general, the research team will focus on the reaction of nitrogen and water to produce ammonia, the precursor to all nitrogen-based agricultural fertilizers. Ammonia is currently industrially produced by a century-old process which has a large carbon footprint and requires large, centralized processing plants. This project has the potential to advance national health, prosperity, and welfare, by developing a sustainable and geographically distributed process for ammonia synthesis. Students will receive experiential learning through visits to local farms, which will provide them with the socioeconomic context to motivate their research. This project will develop in-situ spectroscopic techniques to characterize the interfacial chemistry between an atmospheric-pressure plasma and liquid water. Gas-phase activation of dinitrogen will be characterized by optical emission spectroscopy and laser diagnostics. A major focus of the project will be to implement in-situ surface-enhanced Raman scattering spectroscopy to detect intermediates formed near the plasma-liquid interface by dissociation of gas-phase species and subsequent reaction in the liquid phase. The fundamental knowledge of plasma-induced chemical reactions generated by the gas and liquid phase measurements will be combined with two engineering strategies to improve product yields and energy efficiency: pulsed operation of the plasma to maintain low gas-phase temperatures and the introduction of water droplets or water vapor to increase the size of the plasma/water interfacial area. The outcomes of the proposed work will be a deeper understanding of reaction pathways induced by a plasma at the surface of a liquid, elucidation of unique aspects relative to other alternative methods of dinitrogen activation, and a path forward for optimization of plasma–liquid processes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.