2D Ag-Doped Cu–Zn–Sn–S Nanosheets for the Electrocatalytic Nitrate Reduction Reaction

The electrocatalytic nitrate reduction reaction (NO3RR) has been receiving increasing attention for ammonia (NH3) production, but it still faces great difficulty in real applications due to low NH3 selectivity and high nitrite (NO2–) residue, necessitating an intermediate pathway and microenvironment modulation beyond active sites. Here, we report a quasi-homogeneous nanoreactor via in situ NO3–-mediated reconstruction in 2D Ag-doped Cu–Zn–Sn–S nanosheets for efficient NO3RR with ultralow NO2– release. Both Ag doping and NO3– were found to be critical during the reconstruction process, resulting in increased bidentate NO3– as a key intermediate. The catalyst achieves a high NH3 yield of 0.33 mmol h–1 cm–2 and Faradaic efficiency (FE) of 91.04% with an extremely low yield of NO2– (2.57 ppm). In situ spectroscopies further evidence the quasi-homogeneous phase with greatly enhanced adsorption of both NO3– and H2O, favoring restricted and directional conversion to *NO2 and ultimately strong *NH3 with negligible NO2– release. Moreover, the catalyst in a flow cell delivers an increased NH3 yield and maintains low NO2– release (<15 ppm) under widely varied concentrations and potentials simulating industrial conditions. This study provides a substrate-mediated reconstruction strategy toward a quasi-homogeneous active phase for high-selectivity NO3RR, which is also inspiring for other complex reactions.