Fabrication of porous nanosheet-based Co₃O₄ hollow nanocubes for electrochemical capacitors with high rate capability

Highlights: • Hierarchical Co₃O₄ hollow nanocubes can be synthesized by a Cu₂O template method. • Shells of Co₃O₄ are porous and built up of many interlaced ultrathin nanosheets. • Samples can work as high rate capability electrode materials for supercapacitors. - Abstract: Well-defined hierarchical Co₃O₄ hollow nanocubes with uniform porous structures and high specific surface area have been synthesized by Cu₂O template-assisted method combing a post-calcination process in air. Results show that the obtained hollow Co₃O₄ nanocubes are porous in their shells, which are built up of many interlaced ultrathin nanosheets (∼5 nm in thickness). Both nanosheet networks and porous interconnections within hollow nanocubes can facilitate the transportation of electrons and electrolyte ions, and accordingly result in high electrochemical performances. As is expected, these Co₃O₄ nanocubes exhibit a specific capacitance (404.9 F g^–1 at a charge-discharge current density of 0.5 A g^–1), excellent rate capability (87.8% capacity retention at 20 A g^–1), and good cycling stability (about 5% lose after 2000 cycles). Moreover, the assembled asymmetric systems using activated carbon as negative electrode can output a high energy density of 21.8 W h kg^–1 at power density of 0.4 kW kg^–1; even maintain 51.8% at a high power density of 8 kW kg^–1, further showing high rate capability.