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

Abstract

AbstractTandem 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.