Upscaling of electrochemical nitrogen reduction to ammonia: From batch to flow cells

Research output: Book/ReportPh.D. thesis

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Abstract

Synthetic production of ammonia was made possible in the beginning of the 20th century, where the Haber-Bosch process was invented. This made it possible to produce large volumes of ammonia, which otherwise was a limited commodity from natural sources. Ammonia is an essential chemical for the world as we know it, since it is mainly used for fertilizers. With synthetic fertilizers, farming can be done much more effective, increasing the crop-yield. More crops, mean more food to more people. And so, during the last century, the global population has increased four-fold, thanks to the Haber-Bosch process. In this process, nitrogen and methane is converted, forming ammonia and carbon dioxide as a by-product. Splitting inert nitrogen gas is a difficult process, which here requires high temperature and pressure. To do this efficiently, the production-plants are large and centralized. Due to the large scale, and current yearly production volume of >180 million tonnes per year, the process is responsible for more than 1% of the global CO2-emissions. With an increase in the global population, the emissions will follow along. So to meet the current climate actions, improvements or alternatives must therefore be found.
In this thesis, an alternative electrochemical method for ammonia synthesis is
discussed. It was first proposed in 1930 by Fichter et al., and later again in 1993
by Tsuneto et al. But only within the last few years, the method has gained
worldwide attention, after it was proven by Andersen et al. to be able to break
the strong nitrogen triple-bond. The synthesis is based on a lithium-mediated
reaction, where reactive metallic lithium spontaneously allows the process to proceed. It draws many parallels to battery research, operating in non-aqueous conditions.
Most studies on this electrochemical process, are done in small-scale batches, with minute amounts of ammonia produced. The focus of this thesis, is  to develop an upscaled electrochemical cell, not limited by batch-wise production. It should be larger in size, and capable of flowing both liquid electrolyte, and gas reactants. These are key elements for allowing continuous production of ammonia.
The thesis starts with a brief introduction to the importance of ammonia. Subsequently, an introduction to some fundamentals on reactions and catalysis, and the experimental methods used for this work. The following chapter will cover the lithium-mediated reaction, and what we know so far. Then the development process, and challenges faced for realizing a working cell, are described. It will end with measurements on the operation of this cell, where mass spectrometry was used for detection and determination of the origin of reactants.
Original languageEnglish
PublisherDepartment of Physics, Technical University of Denmark
Number of pages188
Publication statusPublished - 2022

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