Upshifting Lithium Plating Potential To Enhance Electrochemical Lithium Mediated Ammonia Synthesis

Abstract

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.