(697b) Lithium Mediated Electrochemical Synthesis of Ammonia at High Pressures

NH₃ is an important commodity chemical used to produce fertilizers, explosives, pharmaceuticals, textiles, etc. NH₃ is produced by a century-old Haber-Bosch process that is responsible for 1-2% of the total greenhouse gas emissions.¹ It is desired to decarbonize NH₃ synthesis and green NH₃ is one of the candidate materials for H₂ storage. Li-mediated electrochemical synthesis of NH₃ provides a sustainable and environment-friendly way to make green NH₃. Great progress has been made in the Li-mediated NH₃ synthesis, but the process suffers from low NH₃ current densities, higher cell potentials, and poor electrolyte and substrate stability. For commercializing this technology, we need to solve these challenges. In this study, we address these challenges by choosing an efficient catalyst substrate, electrolyte, protonating source, and reactor design. We enhance the ammonia yield and selectivity by performing the reaction at high pressures ranging from 10-100 bar. A custom electrochemical reactor setup is developed by modifying the autoclave to withstand pressures up to 300 bar. High pressures improve the solubility and diffusion of gaseous nitrogen in non-aqueous solvents, therefore enhancing Lithium nitridation. Various substrates for Li deposition have been studied to optimize the system's performance and Copper electrodeposited on nickel foam is identified as the most promising substrate. Various electrolyte compositions are studied with varying base electrolytes such as THF, propylene carbonate, acetonitrile, and Dimethyl sulfoxide (DMSO). LiOCl₄ gives the best Lithium deposition rates. Overall, we report an enhanced NH₃ current density of ~-100 mA/cm² with 50 % NH₃ Faradaic efficiency which is the highest reported so far in the literature. The system remains stable for the studied time of 8h.

References

1. Capdevila-Cortada, M. Electrifying the Haber–Bosch. Nat Catal 2, 1055 (2019)