Metal–organic framework-derived hierarchical Co3O4@MnCo2O4.5 nanocubes with enhanced electrocatalytic activity for Na–O2 batteries

Abstract

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@MnCo₂O_4.5 nanocubes (h-Co₃O₄@MnCo₂O_4.5 Ns) with a yolk–shell structure are designed for the first time as the novel O₂ electrode. h-Co₃O₄@MnCo₂O_4.5 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@MnCo₂O_4.5 active sites. These unique structural properties endow h-Co₃O₄@MnCo₂O_4.5 Ns with remarkably enhanced electrocatalytic activity towards both the ORR and OER. The Na–O₂ battery based on h-Co₃O₄@MnCo₂O_4.5 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.