Lithium-mediated ammonia synthesis from water and nitrogen: a membrane-free approach enabled by an immiscible aqueous/organic hybrid electrolyte system

Abstract

The lithium-mediated pathway provides a promising way for facile and selective dissociation of nitrogen for ammonia synthesis. However, the prevailing electro-deposition of lithium, especially when coupled to the anodic oxygen evolution from water or hydroxide, presents disadvantages including the use of expensive Li-ion conducting ceramics (LISICON) or high temperature operation of molten salts. In this study, a membrane-free approach based on the immiscibility of aqueous/organic electrolytes was adopted for lithium electro-deposition, which could be utilized for subsequent nitridation and ammonia synthesis. We found that a biphasic system of aqueous 1 M LiClO₄ and 1 M LiClO₄/propylene carbonate reinforced with PMMA (poly(methyl methacrylate)) acts the same as a LISICON-based aqueous/organic hybrid electrolyte system, but without any physical membrane. With a fairly high faradaic efficiency (FE) of 57.2% and a production rate of 1.21 × 10⁻⁹ mol cm⁻² s⁻¹ for ammonia synthesis, this membrane-free approach and its application to ammonia synthesis provide an innovative way to the advancements in next-generation energy storage technologies.