Lithium-Mediated Ammonia Synthesis from Water and Nitrogen Based on a Membrane-Free Immiscible Aqueous/Organic Hybrid Electrolyte System

Abstract

Lithium-mediated pathway provides a promising way for facile and selective dissociation of nitrogen for ammonia synthesis [1,2]. 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[3] or high temperature operation of molten salts[1]. Herein, we reported a membrane-free electrochemical system for Li deposition which relies on the immiscibility of aqueous/organic electrolytes and demonstrated the applicability of the biphasic system for the realization of Li-mediated ammonia synthesis. The behavior of this system is not different from a LISICON-based cell,[1] especially thanks to the stability of the biphasic system. Rather, this system requires lower cell voltage (5.3 V in this study vs. 6.2 V in LISICON-based cell[3] at 5 mA cm-2), even without the need of expensive membrane, rendering it more economically favorable. The fairly decent FE and NH3 synthesis rate (57.2 % and 1.21 × 10-9 mol cm-2s-1, respectively) have been realized merely using one hybrid model electrolytes system (LiClO4 and PC-H2O) without any optimization. Judicious selection of immiscible electrolytes with better biphasic stability, higher conductivity, higher stability against Li (lower SEI formation), and applicability to a continuous, integrated process will achieve further improvements in the novel Li-mediated NH3 synthesis approach.