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

Electrocatalytic NO 3 – synthesis of NH 3 (NO 3 RR) presents a promising alternative to the traditional Haber–Bosch process. However, The NO 3 RR is a complex process that converts NO 3 – to NH 3 through a series of nitrogen-containing intermediates, such as NO 2 –, 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 NH 3 synthesis from NO 3 – and design an Ag-GO-Hemin-His tandem catalyst to optimize the kinetic rate of the NO 3 RR intermediate reaction. In situ infrared and activation energy studies revealed that Ag serves as the first active center, rapidly promoting the conversion of NO 3 – to NO 2 –, while FeN 5 in GO-Hemin-His acts as the second active center, efficiently facilitating the reduction of NO 2 – to NH 3 . This dual active-center catalyst lowered the energy barrier of the rate-determining step in the NO 3 RR process from 11.7 to 8.29 kJ mol –1, achieving a high Faraday efficiency (FE) of 91.9% and an impressive NH 3 yield rate of 3.80 mg h –1 cm –2 in a 1 M KOH and 0.1 M KNO 3 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 NH 3 generation.