Thesis Colloquium: A Few Case Studies of Materials Designed for Electrochemical Nitrogen Reduction for Ammonia Synthesis and Rechargeable Li-N2 Battery

Ammonia (NH₃) is a cornerstone of the fertilizer industry, with approximately 80% of its global production used to sustain agriculture and feed the global population [1, 2]. Beyond its role in agriculture, NH₃ is a carbon-free energy carrier, which may beneficially address key challenges related to hydrogen (H2) transportation and storage costs. The synthesis of NH₃ is predominantly achieved using the conventional century-old Haber-Bosch process. Despite its effectiveness, the Haber-Bosch process is highly energy-intensive and contributes 1–2% of global artificial carbon dioxide (CO2) emissions. To achieve net-zero emissions by 2050, developing green and sustainable alternatives to the Haber-Bosch process is imperative. Electrochemical nitrogen reduction (eNRR) offers a promising, eco-friendly pathway to ammonia production, paving the way toward a zero-carbon future centered on ammonia and hydrogen as sustainable energy solutions.

This thesis focuses on electrocatalyst design [3] and optimization of electrolyte compositions for electrochemical N2 fixation and application in metal-nitrogen batteries. The first part addresses electrocatalyst and electrolyte optimization for the eNRR. Selecting an appropriate catalyst is challenging due to competition with the H2 evolution reaction (HER). This work emphasizes the importance of electrocatalysts that preferentially bind N₂ over H₂ and demonstrates how strategic modifications can enhance eNRR performance. Additionally, the thesis tackles the issue of low N2 availability [4] in aqueous electrolytes for eNRR at the electrode surface. Using organic acids as electrolytes improves N2 availability in the solution, increasing the NH3 formation rate. The second part of this thesis investigates N2 fixation in a Li- N2 battery [5-7], highlighting its potential for energy storage and conversion. It addresses challenges such as gas crossover [7] effects and their impact on battery lifespan, providing a detailed analysis of the discharge products and the Faradic efficiency achieved in the system. The work accomplished as part of this thesis will aid in advancing the knowledge of the underlying principles of eNRR to NH3 and associated chemicals/processes. This will open up a new paradigm for sustainable synthesis of ammonia.

1. MacFarlane, D. R.; Cherepanov, P. V.; Choi, J.; Suryanto, B. H. R.; Hodgetts, R. Y.; Bakker, J. M.; Ferrero Vallana, F. M.; Simonov, A. N. A Roadmap to the Ammonia Economy. Joule 2020, 4,6, 1186-1205.