Matched Kinetics Process Over Fe 2 O 3 -Co/NiO Heterostructure Enables Highly Efficient Nitrate Electroreduction to Ammonia.

Tandem nitrate electroreduction reaction (NO 3 - RR) is a promising method for green ammonia (NH 3 ) synthesis. However, the mismatched kinetics processes between NO 3 - -to-NO 2 - and NO 2 - -to-NH 3 results in poor selectivity for NH 3 and excess NO 2 - evolution in electrolyte solution. Herein, a Ni 2+ substitution strategy for developing oxide heterostructure in Co/Fe layered double oxides (LDOs) was designed and employed as tandem electrocataltysts for NO 3 - RR. (Co 0.83 Ni 0.16 ) 2 Fe exhibited a high NH 3 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 NH 3 evolution over (Co 0.83 Ni 0.16 ) 2 Fe, with Ni playing a dual role in NO 3 - 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 2 and its subsequent hydrogenation on the Co sites became more thermodynamically feasible. This study shows that Ni substitution promotes the kinetics of the NO 3 - RR and provides insights into the design of tandem electrocatalysts for NH 3 evolution.