The electrochemical production of ammonia from dinitrogen and urea from waste CO₂ and nitrate, driven by renewable energy, provides a unique opportunity to both store renewable energy in chemical bonds and produce carbon-neutral artificial fertilizers. Dinitrogen can be electrochemically reduced with lithium as a mediator (Li-NRR) in non-aqueous electrolytes, whereas urea can be produced from CO₂ and nitrate co-reduction.

In this talk, I will first discuss the relationship between the applied potential and Li-NRR performance indicators, such as the FE_NH3, R_NH3 and reaction stability. We identify three potential regimes, where the current response up to -3.2 V vs SHE is the most stable, but at the cost of a relatively low performance. At more negative potentials Li-NRR performance increases, but beyond -4.0 V vs SHE, breakdown of the current response is observed. A strong positive correlation is observed between the FE_NH3 and the LiF concentration, which increases at more negative applied potentials. Thicker and denser SEI morphologies are also beneficial for the FE_NH3, while they can be responsible for the observed current instabilities beyond -4.0 V vs SHE. These findings improve the current understanding of the SEI formation process and sheds light on a new optimization strategy for Li-NRR systems, which contribute to the development of a sustainable ammonia production process.

Second, I will discuss the design of detailed process models for the electrochemical production of NH₃ [1]. These models are used to gain insights into the main bottlenecks of the process and to understand what process conditions are required to reach economic parity with SMR Haber-Bosch. We find that the inherently low energy efficiency (EE) of Li-NRR electrolyzers cause disproportionally high operational costs. The EE can be improved by developing MEA-type electrolyzers to circumvent electrolyte conductivity losses or by implementing an alternative mediator with a more positive plating potential than Li, such as Mg or Al.

Finally, I will discuss the development and optimization of a hybrid flow cell reactor based on a modified membrane electrode assembly configuration for CO₂ and nitrate co-reduction to urea. The results collectively highlight that the performance, selectivity towards urea, and stability of the hybrid flow cell system are governed by the subtle interplay between ion transport, electrolyte composition, and interfacial reaction conditions.