Recent advancements in metal-free nitrides based single-atom catalysts: Nanoarchitectonics and applications

Metal-free nitrides (MFNs) including carbon nitride (CN), boron nitride (BN), and borocarbonitride (BCN), have shown immense potential as single metal atom catalysts (SACs). They can act as excellent host support for anchoring and stabilizing single metal atoms. However, critical challenges related to the precise loading of single metal atoms and their accurate characterization are still being pursued. The current review explores the various aspects of MFNs-SACs. Synthesis methods including carbonization, self-assembly, microwave, ball milling and atomic layer deposition are discussed. Characterisation using X-ray absorption, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), Wavelet transform extended X-ray absorption fine structure (WT-EXAFS), and scanning transmission electron microscopy (STEM) which are useful to explore atomic-level structure and coordination of the MFNs-SACs are discussed in depth. The theoretical understanding of the structural framework of the MFNs-SACs using the packages including Vienna ab initio simulation (VASP), projector-augmented wave (PAW), Perdew-Burke Ernzerhof (PBE) and spin-polarized DFT is discussed in detail. A comprehensive discussion of electrocatalytic and photocatalytic applications of MFNs-SACs is evaluated. In the end, conclusions and future outlooks are provided with a focus on what is already achieved and what further can be achieved in the field by utilizing advanced scientific research and knowledge.