Ag‐Co3O4‐CoOOH‐Nanowires Tandem Catalyst for Efficient Electrocatalytic Conversion of Nitrate to Ammonia at Low Overpotential via Triple Reactions

Abstract 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.