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 e_g-electron availability for nitrite-to-ammonia conversion. Here, B-site Ni regulation yields a more dispersed LaMnO₃ nanoperovskite, LaMn_0.95Ni_0.05O₃ (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.