Ag-Co 3 O 4 -CoOOH-Nanowires Tandem Catalyst for Efficient Electrocatalytic Conversion of Nitrate to Ammonia at Low Overpotential via Triple Reactions.

The electrocatalytic conversion of nitrate (NO 3 ‾) to NH 3  (NO 3 RR) offers a promising alternative to the Haber-Bosch process. However, the overall kinetic rate of NO 3 RR is plagued by the complex proton-assisted multiple-electron transfer process. Herein, Ag/Co 3 O 4 /CoOOH nanowires (i-Ag/Co 3 O 4  NWs) tandem catalyst is designed to optimize the kinetic rate of intermediate reaction for NO 3 RR simultaneously. The authors proved that NO 3 ‾ ions are reduced to NO 2 ‾ preferentially on Ag phases and then NO 2 ‾ to NO on Co 3 O 4  phases. The CoOOH phases catalyze NO reduction to NH 3  via NH 2 OH intermediate. This unique catalyst efficiently converts NO 3 ‾ to NH 3  through a triple reaction with a high Faradaic efficiency (FE) of 94.3% and a high NH 3  yield rate of 253.7 μmol h -1  cm -2  in 1 M KOH and 0.1 M KNO 3  solution at -0.25 V versus RHE. The kinetic studies demonstrate that converting NH 2 OH into NH 3  is the rate-determining step (RDS) with an energy barrier of 0.151 eV over i-Ag/Co 3 O 4  NWs. Further applying i-Ag/Co 3 O 4  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 NH 3  production.