Cation Substitution Strategy for Developing Perovskite Oxide with Rich Oxygen Vacancy-Mediated Charge Redistribution Enables Highly Efficient Nitrate Electroreduction to Ammonia

[Image: see text] The electrocatalytic nitrate (NO(3)(–)) reduction reaction (eNITRR) is a promising method for ammonia synthesis. However, its efficacy is currently limited due to poor selectivity, largely caused by the inherent complexity of the multiple-electron processes involved. To address these issues, oxygen-vacancy-rich LaFe(0.9)M(0.1)O(3−δ) (M = Co, Ni, and Cu) perovskite submicrofibers have been designed from the starting material LaFeO(3−δ) (LF) by a B-site substitution strategy and used as the eNITRR electrocatalyst. Consequently, the LaFe(0.9)Cu(0.1)O(3−δ) (LF(0.9)Cu(0.1)) submicrofibers with a stronger Fe–O hybridization, more oxygen vacancies, and more positive surface potential exhibit a higher ammonia yield rate of 349 ± 15 μg h(–1) mg(–1)(cat.) and a Faradaic efficiency of 48 ± 2% than LF submicrofibers. The COMSOL Multiphysics simulations demonstrate that the more positive surface of LF(0.9)Cu(0.1) submicrofibers can induce NO(3)(–) enrichment and suppress the competing hydrogen evolution reaction. By combining a variety of in situ characterizations and density functional theory calculations, the eNITRR mechanism is revealed, where the first proton–electron coupling step (*NO(3) + H(+) + e(–) → *HNO(3)) is the rate-determining step with a reduced energy barrier of 1.83 eV. This work highlights the positive effect of cation substitution in promoting eNITRR properties of perovskites and provides new insights into the studies of perovskite-type electrocatalytic ammonia synthesis catalysts.