Biomimetic-Based Design of Tandem Catalysts for Efficient Nitrate to Ammonia Conversion

Electrocatalytic NO3– synthesis of NH3 (NO3RR) presents a promising alternative to the traditional Haber–Bosch process. However, The NO3RR is a complex process that converts NO3– to NH3 through a series of nitrogen-containing intermediates, such as NO2–, NO–, NOH, etc. This transformation involves 8-electron and 9-proton couplings, resulting in a slow overall reaction rate. Herein, we mimic the dual active-center mechanism found in nature for NH3 synthesis from NO3– and design an Ag-GO-Hemin-His tandem catalyst to optimize the kinetic rate of the NO3RR intermediate reaction. In situ infrared and activation energy studies revealed that Ag serves as the first active center, rapidly promoting the conversion of NO3– to NO2–, while FeN5 in GO-Hemin-His acts as the second active center, efficiently facilitating the reduction of NO2– to NH3. This dual active-center catalyst lowered the energy barrier of the rate-determining step in the NO3RR process from 11.7 to 8.29 kJ mol–1, achieving a high Faraday efficiency (FE) of 91.9% and an impressive NH3 yield rate of 3.80 mg h–1 cm–2 in a 1 M KOH and 0.1 M KNO3 solution at −0.5 V versus RHE. Furthermore, the zinc nitrate battery, assembled with Ag-GO-Hemin-His as the cathode material, exhibited a high power density of 3.28 mW cm–2 and an impressive FE of 88.6% for NH3 generation.