Efficient nitrite-to-ammonia electroreduction on single Ag sites

[Display omitted] •Single-atom Ag on hexagonal BN nanosheets (Ag1@h-BN) is explored as an efficient NO2RR catalyst.•Ag1@h-BN shows a NH3-YS of 1523.6 μmol h−1 cm−2 and NH3-FE of 92.04% at a high current density of 266.2 mA cm−2.•Single-site Ag synergistically boosts NO2– activation/hydrogenation and retards the competing H2 evolution.•This work provides in–depth insights into h-BN-loaded SACs as efficient NO2RR catalysts for NO2–-to-NH3 conversion. Electroreduction of nitrite to ammonia (NO2RR) provides an innovative route for simultaneously achieving waste NO2– removal and valuable NH3 production. Herein, single-atom Ag on hexagonal BN nanosheets (Ag1@h-BN) is developed as an efficient catalyst for the NO2RR. Strikingly, Ag1@h-BN assembled in a flow cell shows the highest NH3-Faradaic efficiency of 92.04 % with the corresponding NH3 yield rate of 1523.6 μmol h−1 cm−2 at a high current density of 266.2 mA cm−2. Theoretical calculations and electrochemical spectroscopic measurements unveil the creation of Ag1-N3 site to selectively activate NO2– and boost the hydrogenation energetics of NO2–-to-NH3 pathway, consequently resulting in the substantially expedited selectivity and activity of Ag1@h-BN for the NO2RR.