Upshifting Lithium Plating Potential To Enhance Electrochemical Lithium Mediated Ammonia Synthesis

The electrochemical lithium-mediated N2 reduction is a promising process for sustainable ammonia synthesis. Unfortunately, fundamental understanding linking the interfacial chemistry of lithium plating with ammonia efficiency is not well understood. We investigated a series of tetrahydrofuran electrolytes (LiClO4, LiBF4, LiTFSI, LiFSI) at 0.2-7.0 M. The Li+/Li potential (ELi+/Li) measured against the electrolyte-invariant Me10Fc reference increased with more dissociative salts and higher concentration. The upshift in ELi+/Li was found to correlate with greater ammonia production stability and faradaic efficiency as well as the production rate. This correlation could be attributed to altered solid-electrolyte interphase (SEI), which revealed prominent anion-derived (LiF) and alkoxide (LiOEt) species with increasing ELi+/Li from Raman spectroscopy, potentially providing more LixN and enhanced ion transport. Such insights can be used to guide the design of electrolytes to promote lithium-mediated ammonia synthesis for practical applications.