Tailored Bimetallic Ni–Sn Catalyst for Electrochemical Ammonia Oxidation to Dinitrogen with High Selectivity

Direct electrochemical ammonia oxidation reaction (eAOR) is an efficient and sustainable strategy to process wastewater containing ammonia, and it endures overoxidation and severely competitive oxygen evolution reaction (OER). Herein, we synthesized a Ni(OH)₂/SnO₂ composite catalyst by a multistep strategy and applied it to the eAOR process. Ni(OH)₂/SnO₂ exhibited a N₂-N Faradaic efficiency (FE_N2-N) of 84.2%, with a N₂ partial current density (j_N2-N) of 2.7 mA cm^-2 at 1.55 V vs reversible hydrogen electrode (RHE) in 0.5 M K₂SO₄ with 10 mM NH₃-N (pH 11). The oxophilic Sn promoted NH₃ absorption on Ni sites while suppressing the OER. As the active species, NiOOH accelerated the dimerization of intermediates (*NH₂ or *NH) to form N₂.