Matched Kinetics Process Over Fe₂O₃‐Co/NiO Heterostructure Enables Highly Efficient Nitrate Electroreduction to Ammonia

Abstract

Tandem nitrate electroreduction reaction (NO3‐RR) is a promising method for green ammonia (NH3) synthesis. However, the mismatched kinetics processes between NO3‐‐to‐NO2‐ and NO2‐‐to‐NH3 results in poor selectivity for NH3 and excess NO2‐ evolution in electrolyte solution. Herein, a Ni2+ substitution strategy for developing oxide heterostructure in Co/Fe layered double oxides (LDOs) was designed and employed as tandem electrocataltysts for NO3‐RR. (Co0.83Ni0.16)2Fe exhibited a high NH3 yield rate of 50.4 mg·cm‐2·h‐1 with a Faradaic efficiency of 97.8% at ‐0.42 V vs. reversible hydrogen electrode (RHE) in a pulsed electrolysis test. By combining with in situ/operando characterization technologies and theoretical calculations, we observed the strong selectivity of NH3 evolution over (Co0.83Ni0.16)2Fe, with Ni playing a dual role in NO3‐RR by i) modifying the electronic behavior of Co, and ii) serving as complementary site for active hydrogen (*H) supply. Therefore, the adsorption capacity of *NO2 and its subsequent hydrogenation on the Co sites became more thermodynamically feasible. This study shows that Ni substitution promotes the kinetics of the NO3‐RR and provides insights into the design of tandem electrocatalysts for NH3 evolution.