Electrochemical ammonia (NH3) synthesis is a promising technology for sustainable NH3 production that does not require H2 extraction from natural gas or coal which results in significant amounts of CO2 emissions. However, in aqueous electrolytes, the kinetics of H2O reduction (or proton coupling) into H2 is much faster than that of N2 reduction, leading to the dominance of the H2 evolution reaction. To address these challenges, the Li-mediated electrochemical N2 reduction reaction (Li-NRR) has been investigated in polar aprotic organic solvents, and a high NH3 production rate and faradaic efficiency (F.E.) have been obtained. Although significant progress has been made in the Li-NRR, the sustainability of the reaction system remains questionable. As an anode reaction, sacrificial oxidation of the THF-based electrolyte is exploited and the electrolyte undergoes oxidative chemical transformations. To prevent electrolyte degradation at the anode, the H2 oxidation reaction has been derived by supplying additional H2. However, such a methodology is a paradoxical approach to the original purpose of electrochemical NH3 synthesis to replace the proton source for NH3 with H2O from H2. Nevertheless, the absence of H2O (or a low concentration of H2O) is a prerequisite for the Li-NRR; thus, attempts to provide H2O as a proton source for NH3 have not yet been made. In this presentation, we show a biphasic hybrid electrolyte system consisting of an organic solvent catholyte and aqueous anolyte to supply the proton from H2O oxidation (O2 evolution reaction) for electrochemical NH3 synthesis. A comparable NH3 production rate and F.E. could be achieved in the hybrid system using H2O as the proton source, similar to those of the conventional one-compartment Li-NRR system. The hybrid electrolyte system maintains ~60% of NH3 F.E. for 50 h without the electrolyte degradations at a current density of −5 mA cm−2. We expect that this hybrid electrolyte system holds the potential to extend the applications of electrochemical conversion reactions beyond the Li-NRR system.
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