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

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.