(428f) Theoretical Insight into the Surface Dynamics of Lithium-Mediated Nitrogen Activation

The electrochemical synthesis of ammonia, an important chemical which is conventionally synthesized industrially by the highly centralized Haber-Bosch process, holds promise for more sustainable and decentralized production. A lithium metal mediated reduction of nitrogen, involving applying a strongly reducing potential to a metal electrode in a nonaqueous electrolyte containing a lithium salt, has reproducibly demonstrated electrochemical production of ammonia[1,2,3]. The reduction of the lithium ions from the electrolyte to lithium metal or other solid lithium phase at the catalytic surface is hypothesized to play a dominant role in the activation of nitrogen, but the composition and structure of the catalytically active phase is not fully understood presently. Initial theoretical studies have shed light on the possible catalytic role of lithium metal as well as lithium nitride and hydride phases. Due to the ease of diffusion of species within lithium and its high reactivity, understanding the composition and properties of the catalytically active phase and the reaction dynamics within this phase are active areas of research.

In this work, density functional theory based molecular dynamics simulations, and enhanced sampling methods such as metadynamics, are used to simulate the reaction dynamics at finite temperature. We gain physical insight into the role played by structural fluctuations in nitrogen activation. We calculate the rates of these steps and investigate their dependence on the dynamic structure and composition of the active phase. This work provides new insight into the dynamics of nitrogen activation in lithium-medicated nitrogen activation, and also demonstrates the value of dynamic simulations and enhanced sampling methods for studying chemical reactions in complex environments.

[1] A. Tsuneto et al. Journal of Electroanalytical Chemistry. 1994, 367, 1-2, 183-188.

[2] N. Lazouski et al. Joule. 2019, 3, 4, 1127-1139.

[3] J. A. Schwalbe et al. ChemElectroChem. 2020, 7, 1542.