Modulating tenorite-based bimetallic electrocatalysts for highly selective ammonia oxidation to N₂

Electrochemical ammonia oxidation reaction (EAOR) has emerged as an effective method for treating water containing low NH₃ concentrations. Unlike energy-oriented systems, where oxidation often targets power generation, the selectivity conversion of ammonia to non-toxic nitrogen (N₂) remains a major challenge in complex wastewater matrices. In this study, a series of noble metals were plated onto copper crystals (M-Cu, M = Ru, Rh, Pd, Pt, Ag) aimed at mitigating Cu passivation, thereby enhancing the EAOR performance. The Cu sublayer effectively initiated NH₃ adsorption and dehydrogenation at 0 V (vs. RHE), while the surface M metals improved the electrochemically active surface area, corrosion resistance, and catalytic stability of copper. Among M-Cu electrodes, PtCu and AgCu achieved nearly complete ammonia removal with high N₂ selectivity (> 80%) at + 1.0 V (vs. RHE) and pH 11, and AgCu obtained the lowest energy consumption. Mechanistic analyses revealed that the strong affinity of OH^- to the neighboring M sites lowered the activation barrier for NH_x dehydrogenation mediated by the reversible Cu₂O/CuO redox couple, followed by dimerization to N₂. The treatability of an optoelectronic wastewater (250 mg-N L^-1) was further demonstrated via constant-current electrolysis (2 mA cm^-2) using the M-Cu electrodes and a steady-state kinetic model was established to evaluate the mechanistic insights of the EAOR process.