Nanoscale Ru unlocking nanoneedles assembled into hierarchical CoO microspheres for efficient nitrate-to-ammonia...

Because of the strong ability of cobalt oxide (CoO) to render active hydrogen (*H) for selective hydrogenation of NO₃ ^-, it is well established as a promising catalyst for the electrocatalytic reduction of NO₃ ^- to ammonia (eRNO₃ ^--to-NH₃) for green NH₃ synthesis along with NO₃ ^- pollutant treatment. Unfortunately, its practical application is severely limited by easy agglomeration, weak NO₃ ^- adsorption, and the side reaction of H* coupling, causing the blockage of active sites and low selectivity of NH₃. For this, we purposefully designed a hetero hybrid electrocatalyst (denoted as CoO-Ru/CC), where nano-dimensional metallic Ru is anchored onto nanoneedles assembled into hierarchical CoO microspheres that are self-supported on carbon cloth (CC). Because of the vertical order open architecture, intrinsic oxygen vacancies, and local electric field in the self-standing CoO-Ru heterostructure, there are abundant active sites, efficient adsorption of NO₃ ^-, weakened N-O bonds, and a reduced reaction energy barrier, as well as high reduction selectivity. CoO-Ru/CC efficiently catalyzes eRNO₃ ^- to NH₃ with a high NH₃ yield rate of 2.502 mg h^-1 cm_cat. ^-2 and faradaic efficiency of 93.41%. In situ characterization provided evidence for the *NO₃-*NO₂-*NO-*N-*NH-*NH₃ pathway involving the reaction mechanism for CoO-Ru/CC. Additionally, constructed CoO-Ru/CC-based Zn-NO₃ ^- batteries exhibited remarkable power density. More significantly, the in-depth insights we achieved offer meaningful guidance for rationally designing advanced CoO-based catalysts for high-efficiency eRNO₃ ^--to-NH₃ electroconversion.