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

Electrocatalytic nitrate (NO 3 - ) reduction represents one of the most promising approaches to mitigate NO 3 - pollution and yield NH 3 , 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 → NO 3 - ). Among these examined SACs, the Cu/NC presents good performance toward NH 3 synthesis, i.e., a maximum NH 3 Faradaic efficiency of 100% with a high NH 3 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-N 4 coordination prohibits the formation of N 2 , N 2 O, and H 2 and facilitates the orbital hybridization between the 2p orbitals of NO 3 - 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 NO 3 - reduction to NH 3 .