Single-Atom Sites With Axial Ligand-Induced d Orbital Rearrangement as Efficient Electrocatalysts for Lithium–Oxygen Batteries

Abstract

Understanding and regulating the electronic states of single-atom sites near the Fermi energy level are essential for developing effective electrocatalysts for lithium–oxygen batteries (LOBs). In this study, we introduce an axial oxygen ligand at the metal center of cobalt porphyrin (CoPP) to adjust the electronic state of the Co center. Theoretical calculations and experimental findings show that this axial interaction disrupts the planar tetragonal crystal field of CoPP, resulting in enhanced spin polarization and electronic rearrangement. This rearrangement of d orbitals causes an upward shift in the frontier orbitals, which facilitates electron exchange during reactions. Additionally, the increased number of unpaired electrons in the d orbitals enhances the adsorption of CoPP-O-MXene to various oxygen species, promoting the formation of a thin film-like Li₂O₂. These thin film-like discharge products improve contact with the electrode surfaces, leading to easier decomposition during the charging process. Consequently, CoPP-O-MXene-based LOBs demonstrate a high discharge capacity of 11035 mAh g⁻¹, a low overpotential of 0.76 V, and remarkable cycling stability (445 cycles).

Keywords

axial ligands / electrocatalyst / lithium–oxygen battery / oxygen electrode reaction / single-atom sites

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