Matched Kinetics Process Over FeO-Co/NiO Heterostructure Enables Highly Efficient Nitrate Electroreduction to Ammonia.

Tandem nitrate electroreduction reaction (NO RR) is a promising method for green ammonia (NH) synthesis. However, the mismatched kinetics processes between NO -to-NO and NO -to-NH results in poor selectivity for NH and excess NO evolution in electrolyte solution. Herein, a Ni substitution strategy for developing oxide heterostructure in Co/Fe layered double oxides (LDOs) was designed and employed as tandem electrocataltysts for NO RR. (CoNi)Fe exhibited a high NH yield rate of 50.4 mg ⋅ cm ⋅ h 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 NH evolution over (CoNi)Fe, with Ni playing a dual role in NO 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 *NO and its subsequent hydrogenation on the Co sites became more thermodynamically feasible. This study shows that Ni substitution promotes the kinetics of the NO RR and provides insights into the design of tandem electrocatalysts for NH evolution.