Insights into the Electrochemical Production of Hydrogen Peroxide over Single-Atom Co-N-C Catalysts with the Introduction of Carbon Vacancy Defect near the Co-N4 Site

With the introduction of carbon divacancy, trivacancy, and tetravacancy defects near the Co-N4 site, we have explored the 2e- ORR activity at the Co-N4 site from the perspective of spatial structure and the atomic orbital by DFT calculations. We demonstrate the hybridization strength between Co 3dyz (3dxz) and O 2py (2px) orbitals is the origin of 2e- ORR activity at the Co-N4 site and the hybridization strength relates to the height of the Co 3d projected orbital in the Z direction. The bond length (LCo-O, LO-O), the charge transfer from the Co site to the *OOH adsorbate (Delta QCo-O), the d-band center of the Co site (epsilon d), and the ICOHP value between Co 3d and O 2p orbitals as descriptors can well predict the 2e- ORR activity at the Co-N4 site. This work provides original insights into the 2e- ORR activity over the single-atom Co-N-C catalysts.