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Ammonia-based fertilizers have enabled increases in food production to sustain the world’s population. Currently the major source of ammonia is the Haber-Bosch process, which requires high temperature and pressure and has low conversion efficiency, such that very large plants are required for economical production. Ammonia is therefore one of the most energy and carbon intensive chemical processes worldwide, largely due to the steam methane reforming step to produce the required hydrogen. Because of the very large plant scale and resulting centralization of production, ammonia may also be transported long distances to point of use, adding additional energy and emissions. Distributed, sustainable ammonia production would therefore have a huge impact on global energy use and related carbon emissions. Electrochemical solutions are well-suited to modularity and integration with renewable energy sources and can operate at much milder temperatures and pressures, but a catalyst is needed which is selective to ammonia generation vs competing reactions.
To address the challenge above, Proton OnSite, in collaboration with the University of Arkansas and Case Western Reserve University have demonstrated feasibility for improved ammonia selectivity through tailoring nanoparticle catalyst morphology and using peptides derived from nitrogenase (a nitrogen-splitting enzyme in nature) to direct the desired reaction. Proton’s expertise in electrode fabrication, cell design and water management, combined with the universities’ expertise in catalyst design and synthesis, were combined to fabricate single cell stacks and demonstrate ammonia production from nitrogen over argon controls. The main goal of the next phase is to further enhance the selectivity based on the directions determined in Phase I, and develop an appropriate cell configuration for the resulting electrode.
In Phase I, two peptide sequences from the nitrogenase enzyme and three peptide sequences with varying hydrophobic properties were combined with catalyst nanoparticles derived from the catalyst materials used in the Haber Bosch reaction. Activity for ammonia production was then tested in both beaker cells and full electrodes. Strict protocols were also developed to avoid misleading results from impurities or degradation of components. Two sets of catalysts showed good enhancement of ammonia activity. Based on these results, the Phase II effort will focus in these directions to refine the catalyst activity, while the cell design is also optimized for improved water management. Processes will also be developed for manufacture of the catalyst system at larger scale, for integration with Proton’s existing fabrication capability at scale. This paper will provide a review of the objectives, methodologies, and results of this groundbreaking research project to enhance the efficiency and selectivity of an electrochemical ammonia synthesis process.