Core–Shell Nitrogen‐Doped Carbon Hollow Spheres/Co 3 O 4 Nanosheets as Advanced Electrode for High‐Performance Supercapacitor

Co 3 O 4 /nitrogen‐doped carbon hollow spheres (Co 3 O 4 /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 Co 3 O 4 nanosheets on its surface; while SiO 2 spheres, as a sacrificed‐template, can be dissolved in the process. The prepared Co 3 O 4 /NHCS composites are investigated as the electrode active material. This composite exhibits an enhanced performance than Co 3 O 4 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 Co 3 O 4 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 Co 3 O 4 /NHCS core–shell structure a promising electrode material for high‐performance supercapacitors.