Breaking the Symmetry of Nitrogen-Coordinated Single-Atom Catalysts for Advanced Peroxymonosulfate Oxidation

Tuning the electronic distribution of the single-atom sites in single-atom catalysts (SACs) is crucial for unlocking their catalytic potential. The four-nitrogen-coordinated transitional metal (M-N4) configuration has been widely investigated in peroxymonosulfate (PMS)-based advanced oxidation processes (PMS-AOPs), but restricted by the sluggish electron transfer from PMS to generate the high-valent metal-oxo (HVMO), reactive species with high redox potentials and long half-lives, for the degradation of organic pollutants in water due to its symmetric structure. Recently, the SACs with asymmetric coordination configurations are found to break the symmetric electronic distribution of M-N4, which facilitates the O-H and O-O bond breaking in PMS, thus promoting HVMO formation. Asymmetric coordination has emerged as a novel and effective strategy for single-atom coordination modulation. In this paper, two strategies for breaking the symmetry of nitrogen-coordinated SACs by planar heteroatom doping and axial optimization engineering are outlined, and the reaction mechanisms on the formation of HVMO species over asymmetrically coordinated SACs via PMS activation are highlighted. Finally, we prospect the development of asymmetrically coordinated SACs in water purification. The planar heteroatom doping and the axial coordination engineering are two effective strategies for breaking the symmetry of nitrogen-coordinated single-atom catalysts. This concept describes how these two types of coordination engineering enable high-efficiency activation of peroxymonosulfate as well as highly selective formation of high-valent metal-oxo species at asymmetrically coordinated single-atom sites.image