Lattice Expansion Triggers an N-End Adsorption Pathway for Electrocatalytic Nitrate Reduction to Ammonia

Electrocatalytic nitrate reduction offers a sustainable route for ammonia synthesis and environmental nitrate removal, yet its practical implementation is hindered by a high overpotential and sluggish reaction kinetics. Herein, we propose a rare-earth-mediated strategy using a typical Co₃O₄ electrocatalyst that addresses these limitations through deliberate lattice expansion and electronic restructuring. By incorporating rare-earth Gd³⁺ ions into the Co₃O₄ lattice, it induces pronounced Co-Co bond elongation (from 2.5 to 2.8 Å) and elevates the cobalt oxidation state. These structural and electronic modifications promote charge density redistribution and facilitate interfacial electron transfer. Consequently, the resultant electronic environment switches the primary active sites from bridge-coordinated cobalt (Co_bri) to top-coordinated cobalt (Co_top), favoring a transition from bidentate to N-end adsorption for electrocatalytic nitrate reduction. This reconfiguration stabilizes the critical reaction intermediates and accelerates the hydrogenation kinetics. The optimized Gd-Co₃O₄ catalyst achieves a Faradaic efficiency of 96.2% for NH₄⁺ production at -0.6 V vs RHE, with a record production rate of 5.34 mol·h^-1·gcat^-1 and an industrial-current density of 400 mA·cm^-2 at a 1.9 V cell voltage. Demonstrated across multiple lanthanides (La, Sm, and Gd), this approach provides a universal electronic modulation strategy to overcome overpotential and kinetic barriers in electrocatalytic nitrate reduction.