A-Site Deficiency-Mediated Creation of Oxygen Vacancies in LaMnO_3-δ Nanofibers for Efficient Nitrate Reduction

Electrocatalysis of nitrate to ammonia is retarded by a large dissociation energy and sluggish kinetics, which requires high-efficiency catalysts to reduce the reaction barrier. Herein, creation of oxygen vacancies (Ovs) in LaMnO3−δ (LMO) nanofibers with A-site La deficiency is gradiently mediated through copper doping and hydrogen etching. Both the Faradaic efficiency (FE) and ammonia yield of the etched La0.9Mn0.5Cu0.5O3−δ (R-LMCO) with the most Ovs are significantly increased to 90.1% and 28.1 mg h–1 mgcat.–1. In situ electrochemical Raman spectroscopy verifies the reduction of nitrate, and differential electrochemical mass spectrometry (DEMS) reveals the processes of deoxygenation and hydrogenation at the surface of the catalyst. Density DFT calculations confirm a negative nitrate adsorption free energy of −0.14 eV at R-LMCO, and the d-band centers for La and Cu reach −1.97 and −2.66 eV, respectively, suggesting a strong interaction between intermediates and active sites. This study presents a potential strategy for regulating the Ov concentration to enhance the catalytic activity of nitrate reduction.