Heterogeneous N-coordinated single-atom photocatalysts and electrocatalysts

Single-atom catalysts (SACs) have been widely used in heterogeneous catalysis owing to the maximum utilization of metal-active sites with controlled structures and well-defined locations. Upon tailored coordination with nitrogen atom, the metal-nitrogen (M-N)-based SACs have demonstrated interesting physical, optical and electronic properties and have become intense in photocatalysis and electrocatalysis in the past decade. Despite substantial efforts in constructing various M–N-based SACs, the principles for modulating the intrinsic photocatalytic and electrocatalytic performance of their active sites and catalytic mechanism have not been sufficiently studied. Herein, the present review intends to shed some light on recent research made in studying the correlation between intrinsic electronic structure, catalytic mechanism, single-metal atom (SMA) confinement and their photocatalytic and electrocatalytic activities (conversion, selectivity, stability and etc). Based on the analysis of fundamentals of M–N-based SACs, theoretical calculations and experimental investigations, including synthetic methods and characterization techniques, are both included to provide an integral understanding of the underlying mechanisms behind improved coordination structure and observed activity. Finally, the challenges and perspectives for constructing highly active M–N based photocatalysis and electrocatalysis SACs are provided. In particular, extensive technical and mechanism aspects are thoroughly discussed, summarized and analyzed for promoting further advancement of M-N-based SACs in photocatalysis and electrocatalysis.