Boron and Nitrogen Bridged Mn Single-Atom Catalyst for Highly Efficient Nitrogen Electroreduction to Ammonia

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 (FE_NH3) of ≈37.15% in the aqueous phase system and good electrocatalytic and material stability. The FE_NH3 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 mg_cat. ^-1 h^-1) and FE_NH3 (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.