Manipulating Superexchange Interaction of Ru–O–Fe Sites for Enhanced Electrocatalytic Nitrate-to-Ammonia Selectivity
Mengyang Xia, Chao Zhao, Hang Xiao, Wei Liu, Yang Li, He Li, Honghui Ou, Guidong Yang
Abstract
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 NH 3 production performance. Our experimental and theoretical prediction results confirmed that Ru–O–Fe sites in double perovskite iron oxides (LaFe 0.9 Ru 0.1 O 3 ) 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 NO 3 – adsorption and lowers the hydrogenation energy barrier of the *NO intermediate. Consequently, LaFe 0.9 Ru 0.1 O 3 could efficiently convert NO 3 – to NH 3, achieving rates of 0.75 mmol·h –1 ·cm –2 with a Faraday efficiency of 98.5%. Remarkably, the NH 3 selectivity was as high as 90.7%, which represents almost the best catalyst to date.