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 eg-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 (LaFe0.9Ru0.1O3) 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, eg ≈ 2) to an intermediate-spin state (eg ≈ 1). This transition promotes NO3– adsorption and lowers the hydrogenation energy barrier of the *NO intermediate. Consequently, LaFe0.9Ru0.1O3 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.