Core–Shell Nitrogen‐Doped Carbon Hollow Spheres/Co3O4 Nanosheets as Advanced Electrode for High‐Performance Supercapacitor

Co₃ O₄ /nitrogen-doped carbon hollow spheres (Co₃ O₄ /NHCSs) with hierarchical structures are synthesized by virtue of a hydrothermal method and subsequent calcination treatment. NHCSs, as a hard template, can aid the generation of Co₃ O₄ nanosheets on its surface; while SiO₂ spheres, as a sacrificed-template, can be dissolved in the process. The prepared Co₃ O₄ /NHCS composites are investigated as the electrode active material. This composite exhibits an enhanced performance than Co₃ O₄ itself. A higher specific capacitance of 581 F g^-1 at 1 A g^-1 and a higher rate performance of 91.6% retention at 20 A g^-1 are achieved, better than Co₃ O₄ nanorods (318 F g^-1 at 1 A g^-1 and 67.1% retention at 20 A g^-1 ). In addition, the composite is employed as a positive electrode to fabricate an asymmetric supercapacitor. The device can deliver a high energy density of 34.5 Wh kg^-1 at the power density of 753 W kg^-1 and display a desirable cycling stability. All of these attractive results make the unique hierarchical Co₃ O₄ /NHCS core-shell structure a promising electrode material for high-performance supercapacitors.