Facet-Defect Coupling in CuO Catalysts Boosts Ammonia Oxidation Kinetics

Abstract

The ammonia oxidation reaction (AOR) activity of transition metal oxides is strongly influenced by exposed facets and surface defects; however, their cooperative roles remain insufficiently understood. Herein, we combine a ligand-assisted synthesis strategy with hydrogenation treatment to introduce oxygen vacancies into CuO catalysts with distinct exposed facets, including (020), (002)/(111), and (110), and systematically investigate their influence on AOR performance. Structural and electrochemical analyses reveal that oxygen vacancies alone do not necessarily enhance catalytic activity, whereas their combination with specific exposed facets, particularly (002)/(111), leads to markedly improved AOR performance. Quantitative product analysis further indicates that facet exposure favors N2 formation, while oxygen vacancies promote the generation of oxidized nitrogen species such as NO2- and NO3-, suggesting distinct roles of surface structure and defect sites in determining reaction pathways. Benefiting from the combined influence of surface atomic arrangements and oxygen vacancies, the CuO-SC-AH catalyst achieves a current density of 10 mA cm-2 at 0.37 V vs. SCE, accompanied by a Faradaic efficiency toward N2 exceeding 90%. These results suggest that the interplay between exposed facets and oxygen vacancies contributes to enhanced catalytic performance. This study provides experimental insight into the combined influence of surface structure and defects and offers guidance for the rational design of transition-metal oxide catalysts for electrochemical energy conversion.