Electrocatalytic ammonia oxidation reaction (EAOR) remains hindered by the lack of catalysts that simultaneously achieve high activity and long-term stability. Herein, we report a surface compositional gradient PtFe alloy catalyst (G-PtFe) consisting of a Pt-Fe gradient shell and a PtFe alloy core. The G-PtFe delivers an EAOR current density of 541.7 mA cm⁻², representing an 8.7-fold improvement over pristine Pt, while exhibiting robust poisoning resistance across a wide potential range of 0.5−1.2 V vs. RHE. When employed as anode catalyst in direct ammonia fuel cells, the G-PtFe-based device achieves a peak power density 3.3 times higher than that of commercial Pt/C. Combined experimental analyses and density functional theory simulations reveal that EAOR deactivation on conventional Pt-based catalysts originates from potential-dependent adsorption imbalance: insufficient surface OH adsorption at low potentials promotes the accumulation of N-containing poisoning intermediates, whereas excessive OH binding at high potentials suppresses NH₃ adsorption and induces surface passivation. The surface compositional gradient structure enables dynamically balanced OH and NH₃ adsorption over a wide potential window, resulting in ultra-stable EAOR performance. This work provides mechanistic insights into potential-dependent catalyst poisoning and establishes a surface gradient alloy strategy for rational design of efficient and durable EAOR catalysts.

Electrocatalytic ammonia oxidation reaction (EAOR) provides an ideal solution for on-board hydrogen supply for fuel cells, while the lack of efficient and durable EAOR catalysts has been a long-standing obstacle for its practical application. Herein, we reported that the defect engineering via in-situ electrochemically introducing oxygen vacancies (Vo) not only turns the inactive CuO into efficient EAOR catalyst but also achieves a high stability of over 400 h at a high current density of ~ 200 mA·cm⁻². Theoretical simulation reveals that the presence of Vo on the CuO surface induces a remarkable upshift of the d-band center of active Cu site closer to the Fermi level, which significantly stabilizes the reaction intermediates (*NH_x) and efficiently oxidizes NH₃ into N₂. This Vo-modulated CuO shows a different catalytic mechanism from that on the conventional Pt-based catalysts, paving a new avenue to develop inexpensive, efficient, and robust catalysts, not limited to EAOR.