Evolution of high spin state single-atom catalyst active centers in Na–O2 batteries

Compared to O 2 @MN 4 , O 2 @MN 3 with high spin state favors side-on mode, which enhances the coupling between 3d xy orbital of metal and O 2 , hence causes the evolution of active center from MN 3 to (OMO)N 3 , and increases the performance of Na–O 2 batteries.