Unraveling the Activity Trends and Design Principles of Single-Atom Catalysts for Nitrate Electrocatalytic Reduction

Electrocatalytic nitrate (NO₃^-) reduction represents one of the most promising approaches to mitigate NO₃^- pollution and yield NH₃, but it is still challenged by the atomic economy and selectivity issues of substantial active sites. Here, we describe a comprehensive investigation on a series of single-atom catalysts (SACs) using nitrogen-doped carbon as substrate (metal/NC). The essence of activity is related to the extent of the electron transfer capacity (SAs → NO₃^-). Among these examined SACs, the Cu/NC presents good performance toward NH₃ synthesis, i.e., a maximum NH₃ Faradaic efficiency of 100% with a high NH₃ yield rate of up to 32,300 μg h^-1 mg_cat.^-1. X-ray absorption fine structure spectra and density functional theory calculations provide evidence that the electronic structure of Cu-N₄ coordination prohibits the formation of N₂, N₂O, and H₂ and facilitates the orbital hybridization between the 2p orbitals of NO₃^- and 3d orbitals of Cu single-atom sites. Our study is believed to provide fundamental guidance for the future design of highly efficient electrocatalysts in NO₃^- reduction to NH₃.