Facet engineering has emerged as a promising approach to tailor the catalytic performance of metal oxides for environmental electrocatalysis. Herein, we synthesized spinel Co3O4 nanocrystals with predominantly exposed 110, 111, and 112 facets to investigate their facet-dependent electrocatalytic activity toward chlorine-mediated ammonia oxidation. Structural characterization confirmed the successful fabrication of well-defined 110 nanorods, 111 octahedra, and 112 nanoplates. Electrochemical evaluation revealed a distinct activity trend: 110 > 112 > 111. The Co3O4 110 facet exhibited the lowest chlorine evolution potential, the smallest charge-transfer resistance, and the highest ammonia removal rate, achieving nearly complete oxidation of 75 mg L−1 NH4+-N within 2 h at 15 mA cm−2. Mechanistic studies demonstrated that free chlorine species (HOCl/OCl−), rather than hydroxyl or chlorine radicals, serve as the primary oxidants. XPS and CV analyses further indicated that the superior activity of the 110 facet is attributed to its higher proportion of Co3+ sites and greater oxygen vacancy density, which enhance chloride adsorption and facilitate the Co3+/Co2+ redox cycle critical for the chlorine evolution reaction. This work elucidates the intrinsic structure–activity relationships of Co3O4 facets and provides a rational strategy for designing efficient electrocatalysts for electrochemical ammonia removal.
Shen et al. (Fri,) studied this question.