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

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