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 /SnO 2 composite catalyst by a multistep strategy and applied it to the eAOR process. Ni(OH) 2 /SnO 2 exhibited a N 2 -N Faradaic efficiency (FE N 2 -N ) of 84.2%, with a N 2 partial current density ( j N 2 -N ) of 2.7 mA cm -2 at 1.55 V vs reversible hydrogen electrode (RHE) in 0.5 M K 2 SO 4 with 10 mM NH 3 -N (pH 11). The oxophilic Sn promoted NH 3 absorption on Ni sites while suppressing the OER. As the active species, NiOOH accelerated the dimerization of intermediates (*NH 2 or *NH) to form N 2 .