Nonaqueous Li-Mediated Nitrogen Reduction: Taking Control of Potentials

The performance of the Li-mediated ammonia synthesis has progressed dramatically since its recent reintroduction. However, fundamental understanding of this reaction is slower paced, due to the many uncontrolled variables influencing it. To address this, we developed a true nonaqueous LiFePO4 reference electrode, providing both a redox anchor from which to measure potentials against and estimates of sources of energy efficiency loss. We demonstrate its stable electrochemical potential in operation using different N-2- and H-2-saturated electrolytes. Using this reference, we uncover the relation between partial current density and potentials. While the counter electrode potential increases linearly with current, the working electrode remains stable at lithium plating, suggesting it to be the only electrochemical step involved in this process. We also use the LiFePO4/Li+ equilibrium as a tool to probe Li-ion activity changes in situ. We hope to drive the field toward more defined systems to allow a holistic understanding of this reaction.

Automated summary

The performance of Li-mediated ammonia synthesis has improved significantly since its reintroduction, but the fundamental understanding of this reaction has been slower due to uncontrolled variables. To address this, a nonaqueous LiFePO4 reference electrode was developed, providing a redox anchor for measuring potentials and estimating energy efficiency loss. The relationship between partial current density and potentials was uncovered using this reference, suggesting that only the electrochemical step of lithium plating is involved in the process. The LiFePO4/Li+ equilibrium was also used to probe Li-ion activity changes in situ. The aim is to promote a better understanding of this reaction by developing more defined systems.