Metal-organic framework-derived hierarchical CoO@MnCoO nanocubes with enhanced electrocatalytic activity for Na-O batteries.

The Na-O2 battery system is attracting increasing attention due to its superiority in specific capacity and cost. However, its practical implementation is hindered by many issues, such as high charge-discharge overpotential, limited cycling life, and poor reversibility, all of which result from the mediocre O2 electrode. Herein, to surmount these critical challenges, hierarchical Co3O4@MnCo2O4.5 nanocubes (h-Co3O4@MnCo2O4.5 Ns) with a yolk-shell structure are designed for the first time as the novel O2 electrode. h-Co3O4@MnCo2O4.5 Ns are synthesized from a metal-organic framework via a template-assisted method, which is demonstrated to be helpful in creating a high specific surface area of 130.4 m2 g-1, a hierarchical macro- and mesoporous structure, and synergistic yolk-shelled Co3O4@MnCo2O4.5 active sites. These unique structural properties endow h-Co3O4@MnCo2O4.5 Ns with remarkably enhanced electrocatalytic activity towards both the ORR and OER. The Na-O2 battery based on h-Co3O4@MnCo2O4.5 Ns displays an ultrahigh initial discharge capacity of 8400 mA h g-1, ultralow charge-discharge overpotential of 0.45 V, long cycling life of 135 cycles, and excellent rate capability.