Ni regulated LaMnO3 for selective nitrite to ammonia electroreduction

Air calcination stabilizes LaMnO 3 but can promote particle coarsening and oxidation-driven Mn-valence elevation, reducing Mn e g -electron availability for nitrite-to-ammonia conversion. Here, B-site Ni regulation yields a more dispersed LaMnO 3 nanoperovskite, LaMn 0.95 Ni 0.05 O 3 (LMNO), while coupling oxygen-defect formation with Mn-valence rebalancing without disrupting the LaMnO 3 -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 H 2 O dissociation and initial NO 2 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 NH 3 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 NH 4 Cl recovery, while tests with pretreated landfill leachate show a shift in nitrogen speciation toward NH 4 + and reduced seedling-growth inhibition.