Intercoupled electrocatalytic ammonia synthesis via a looped Li-N<sub>2</sub>/H<sub>2</sub> battery.

Abstract

Electrochemical ammonia (NH₃) synthesis offers a sustainable pathway for the chemical industry. However, the fundamental proton-coupled nitrogen (N₂) reduction process has led to the competing H₂ evolution and low energy efficiency, particularly at high current densities. Herein, we present the design of a looped Li-N₂/H₂ battery that decouples N₂ reduction from protonation by two separate sub-reactions of electrocatalytic N₂ reduction in discharging (6Li⁺ + 6e^- + N₂ → 2Li₃N) and electrocatalytic H₂ oxidation in charging (H₂ → 2H⁺ + 2e^-), which are intercoupled into a synthetic loop to enable NH₃ synthesis (Li₃N + 3H⁺ → NH₃ + 3Li⁺) without H₂ evolution. This approach achieves record-high energy efficiency (26.0% ± 0.9%), Faradaic efficiency (63.7% ± 2.3%), and high NH₃ production rate (1 mA cm^-2, 0.12 mol h^-1 m^-2) under mild conditions. These results significantly lower the cost of ammonia production compared to conventional electrochemical methods, highlighting its promising potential for practical applications.