Ag-Co₃ O₄ -CoOOH-Nanowires Tandem Catalyst for Efficient Electrocatalytic Conversion of Nitrate to Ammonia at Low Overpotential via Triple Reactions

The electrocatalytic conversion of nitrate (NO₃ ‾) to NH₃ (NO₃ RR) offers a promising alternative to the Haber-Bosch process. However, the overall kinetic rate of NO₃ RR is plagued by the complex proton-assisted multiple-electron transfer process. Herein, Ag/Co₃ O₄ /CoOOH nanowires (i-Ag/Co₃ O₄ NWs) tandem catalyst is designed to optimize the kinetic rate of intermediate reaction for NO₃ RR simultaneously. The authors proved that NO₃ ‾ ions are reduced to NO₂ ‾ preferentially on Ag phases and then NO₂ ‾ to NO on Co₃ O₄ phases. The CoOOH phases catalyze NO reduction to NH₃ via NH₂ OH intermediate. This unique catalyst efficiently converts NO₃ ‾ to NH₃ through a triple reaction with a high Faradaic efficiency (FE) of 94.3% and a high NH₃ yield rate of 253.7 μmol h^-1 cm^-2 in 1 M KOH and 0.1 M KNO₃ solution at -0.25 V versus RHE. The kinetic studies demonstrate that converting NH₂ OH into NH₃ is the rate-determining step (RDS) with an energy barrier of 0.151 eV over i-Ag/Co₃ O₄ NWs. Further applying i-Ag/Co₃ O₄ NWs as the cathode material, a novel Zn-nitrate battery exhibits a power density of 2.56 mW cm^-2 and an FE of 91.4% for NH₃ production.