Unsaturated single-atom CoN3 sites for improved fenton-like reaction towards high-valent metal species

High-valent metal species hold promise for selective removal of organic pollutants in wastewater, which necessitate two or more electrons transfer to allow intensive electron from catalysts to PMS. Herein, we design undercoordinated single-atom CoN3 catalyst for boosted generation of high-valent Co species in peroxymonosulfate activation process, to be carefully distinguished from the traditional saturated CoN4 configuration. Enabled by temperature-dependent magnetization measurements, in-situ Raman spectra and electrochemical tests, we found that the unsaturated Co sites in CoN3 with higher spin state can afford enhanced electron-donating ability and intensive electron flow to drive the valence transformation from Co(II) to Co(IV), while the saturated ones in CoN4 with lower spin state only trigger Co(II)/ Co(III) conversion and subsequently produce free radicals. This work highlights the pivotal role of coordination environment for electron flow regulation in Fenton-like catalysts to alleviate water pollution dilemma and advance environmental remediation technologies.