Cobalt-Doped MnO₂Hierarchical Yolk–Shell Spheres with Improved Supercapacitive Performance

Cobalt-doped MnO 2 with a hierarchical yolk–shell spherical structure has been prepared by a light-assisted method. The hierarchical spheres obtained are characterized by X-ray diffraction, nitrogen adsorption–desorption, and electron microscopy analyses. The supercapacitive performance of the material is evaluated by cyclic voltammetry and galvanostatic charge/discharge measurements. A specific capacitance of 350 F g –1 is achieved at a current density of 0.1 A g –1 for the spheres with a Co/Mn ratio of 0.5%, much higher than that of the undoped MnO 2 with a similar hierarchical spherical structure, which is approximately 168 F g –1 . A specific capacitance of 196 F g –1 is still retained after being charged/discharged at a current density of 2.0 A g –1 for 1000 cycles, demonstrating good cycling stability. Over 90% of the initial specific capacitance was retained, exhibiting excellent capacitance retention ability.