In summary, we propose an efficient

In summary, we propose an efficient alternative route for electrochemical ammonia synthesis through electrochemical reduction of nitrate, which is enabled by our demonstration with Cu nanosheets at ambient conditions. Notably, at low overpotential of −0.15 V, Cu nanosheets achieve both high activity (390.1 ug mg−1Cu h−1) and extraordinary selectivity (Faradaic efficiency of 99.7%). Such an ammonia production rate is more than two orders of magnitude higher than that of NRR (i.e. from nitrogen gas). Although at present nitrate is industrially produced from ammonia, which seems opposite to our proposal. With the high efficiency and low energy consumption, our proposed alternative route of NtrRR can still find its applications with waste (e.g. from chemical industry waste or sewage) or cheap (e.g. site of caliche ore) nitrate sources.Moreover, like the hydrogen economy (i.e. a close cycle with H2 and H2O), the nitrogen economy (i.e. a close cycle with NH3, N2,and NO3−) may be another option in the future.