Manipulating Superexchange Interaction of Ru-O-Fe Sites for Enhanced Electrocatalytic Nitrate-to-Ammonia Selectivity

Fe-based catalysts are promising for electrochemical nitrate reduction, but their selectivity is limited by the multielectron/proton transfer reaction steps. Here, we propose optimizing the e_g-orbital electron occupancy by regulating the superexchange interaction of the Fe site to improve the NH₃ production performance. Our experimental and theoretical prediction results confirmed that Ru-O-Fe sites in double perovskite iron oxides (LaFe_0.9Ru_0.1O₃) have more significant superexchange interactions, mainly manifested by O-anion-mediated electron transfer from Ru to Fe cations. Ru alters Fe’s spin configuration through Ru-O-Fe orbital hybridization, transitioning from a high-spin (HS, e_g ≈ 2) to an intermediate-spin state (e_g ≈ 1). This transition promotes NO₃^- adsorption and lowers the hydrogenation energy barrier of the *NO intermediate. Consequently, LaFe_0.9Ru_0.1O₃ could efficiently convert NO₃^- to NH₃, achieving rates of 0.75 mmol·h^-1·cm^-2 with a Faraday efficiency of 98.5%. Remarkably, the NH₃ selectivity was as high as 90.7%, which represents almost the best catalyst to date.