Abstract
Electrochemical ammonia (NH(3)) synthesis offers a sustainable pathway for the chemical industry. However, the fundamental proton-coupled nitrogen (N(2)) reduction process has led to the competing H(2) evolution and low energy efficiency, particularly at high current densities. Herein, we present the design of a looped Li-N(2)/H(2) battery that decouples N(2) reduction from protonation by two separate sub-reactions of electrocatalytic N(2) reduction in discharging (6Li(+) + 6e(-) + N(2) → 2Li(3)N) and electrocatalytic H(2) oxidation in charging (H(2) → 2H(+) + 2e(-)), which are intercoupled into a synthetic loop to enable NH(3) synthesis (Li(3)N + 3H(+) → NH(3) + 3Li(+)) without H(2) evolution. This approach achieves record-high energy efficiency (26.0% ± 0.9%), Faradaic efficiency (63.7% ± 2.3%), and high NH(3) 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.