Abstract

 Ammonia (NH3) is a globally important commodity for energy storage, carbon-free energy carrier, and fertilizer production, but its synthesis through the Haber-Bosch process is energy-intensive and emits significant amounts of CO2. Electrochemical reduction of N2 under ambient conditions is a green and potentially promising approach for NH3 synthesis, but is limited by a high energy barrier of the first *N2 protonation step, competitive hydrogen evolution reaction, and lack of efficient electrocatalysts. Herein, a newly designed electrocatalyst is reported by bridging B2N2 with an Mn single atom in B/N co-doped carbon (denoted MnB2N2/C), which exhibits a highly efficient N2 reduction reaction (N2RR) activity with NH3 Faradaic efficiency (FENH3) of ≈37.15% in the aqueous phase system and good electrocatalytic and material stability. The FENH3 of the MnB2N2/C catalyst is ≈2.1 times higher than that of the as-synthesized MnN4/C counterpart under the same conditions. In the gas phase system, this MnB2N2/C catalyst shows a remarkably high NH3 production rate (87.54 µg mgcat.−1 h−1) and FENH3 (45.66%). The density functional theory (DFT) calculations revealed that the high N2RR to NH3 performance arising from the Mn site and the neighboring B site suppresses the parasitic HER on the Mn sites.