Lithium nitride (Li3N) formation in lithium-mediated electrochemical ammonia synthesis can Be enhanced with the right proton donor

Lithium-mediated electrochemical ammonia synthesis (LiMEAS) hinges on the formation of lithium nitride (Li₃N) from dissociated nitrogen at a lithium surface. Although proton donors (PDs) are known to influence nitrogen activation, their specific role in promoting Li₃N formation is still being investigated. Herein, we employ density functional theory (DFT) to examine the effects of 14 PDs on the stability and energetics of Li₃N formation. We show that in the absence of PD, Li₃N formation is consistently outcompeted by subsurface N₂ embedding and, in some cases, by surface N₂ adsorption. However, the introduction of PD species yields three distinct outcomes: (i) the PD remains intact during Li₃N formation, (ii) the PD protonates Li₃N, or (iii) the PD undergoes structural change. Notably, configurations in which the PD remains intact exhibited greater stability compared to subsurface embedding, driven by PD-induced surface reconstruction. We quantify this reconstruction using a two-layer displacement metric and find a strong correlation between the magnitude of displacement and the system’s overall stability. Further charge analyses show that the enhanced Li₃N stability correlates with a greater electron transfer to nitrogen. Finally, we link the basicity, acidity and polarity of PD with the results of the formation of nitride, demonstrating that the basicity of PD promotes intact configurations Li₃N. In contrast, higher acidity and polarity lead to protonation and alteration of PD. These insights pinpoint a region in the Kamlet–Taft $\beta$$\beta$–$\pi$$\pi$ space where PDs remain intact and foster stable Li₃N, informing future strategies to design more efficient LiMEAS systems.