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 (FEN2–N) of 84.2%, with a N2 partial current density (jN2–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.