Ni regulated LaMnO3 for selective nitrite to ammonia electroreduction.

Air calcination stabilizes LaMnO3 but can promote particle coarsening and oxidation-driven Mn-valence elevation, reducing Mn eg-electron availability for nitrite-to-ammonia conversion. Here, B-site Ni regulation yields a more dispersed LaMnO3 nanoperovskite, LaMn0.95Ni0.05O3 (LMNO), while coupling oxygen-defect formation with Mn-valence rebalancing without disrupting the LaMnO3-type lattice. Combined structural and spectroscopic analyses show stronger oxygen-defect signatures, enhanced lattice-oxygen reducibility, lower average Mn valence, and altered Mn-centered coordination after Ni incorporation. These changes suggest electron compensation of neighboring high-valent Mn species and a more electron-rich Mn-O environment for nitrite activation and hydrogenation. In situ infrared spectroscopy and density functional theory calculations further indicate stepwise intermediate hydrogenation, favorable H2O dissociation and initial NO2 stabilization at Ni sites, Ni 3d and Mn 3d/O 2p states near the Fermi level, and more favorable overall conversion thermodynamics at Ni-regulated Mn sites. LMNO delivers an NH3 yield rate of 8996 μg h-1 cm-2 with 97.3% Faradaic efficiency and remains stable for 400 h. Downstream acid trapping enables crystalline NH4Cl recovery, while tests with pretreated landfill leachate show a shift in nitrogen speciation toward NH4+ and reduced seedling-growth inhibition.