Preparation And Supercapacitive Properties Of Multishelled Transition Metal Oxides Hollow Nanospheres

Hollow structured transition metal oxides with excellent electrochemicalperformance are frequently used as the electrode materials of supercapacitors. Inthis work, we adopt a stepwise immersion coupled with layer-by-layer (LBL)self-assembly method to prepare multishelled NiO hollow nanospheres, and animmersion method to prepare multishelled Co3O4hollow nanospheres usingself-prepared carbon spheres as templates. The structure, formation mechanismand electrochemical performance of these products are investigated and themain contents are as follows:1. Synthesis of multishelled NiO hollow nanosphere samples: We adopt astepwise immersion coupled with layer-by-layer (LBL) self-assembly method.That is, carbon spheres are periodically immersed in Ni2+solution and followedby precipitation of Ni(OH)2precursors in urea solution. And NiO hollownanospheres are obtained through removing the carbon templates by heatingsubsequently. This modified approach has proven the following advantages.Firstly, self-assembly of Ni(OH)2nanoflakes on carbon spheres during theprecipitation process is beneficial to the preparation of the NiO hollownanospheres with hierarchical structures. Secondly, the hollow nanospheres withdesigned number of shells can be easily obtained and are less affected byheating rate. The electrochemical measurements reveal that the double-shelledhollow nanospheres with the largest specific surface area (92.99m2g-1) have thehighest specific capacitance of612.5F g-1compared with single-shelled (432.2F g-1) and triple-shelled hollow nanospheres (292.4F g-1) at0.5A g-1.Furthermore, the double-shelled hollow nanospheres also exhibit highcapacitance retention of90.1%after1000charge-discharge cycles.2. Synthesis of multishelled Co3O4hollow nanosphere samples: Firstly, thecarbon spheres are prepared by a hydrothermal method. Afterwards, the carbonspheres are immersed in Co(NO3)2solution and subsequently calcined in air toobtain multishelled Co3O4hollow nanosphere products. The number of shells isaccurately controlled by adjusting the concentration of the cobalt ions and theheating condition. The formation mechanism of products is investigated and thesupercapacitive performance is measured. The results indicate that the single-shelled Co3O4hollow nanosphere samples with larger specific surfacearea (26.20m2g-1) exhibit higher specific capacitance of (264.1F g-1) thandouble-shelled Co3O4hollow nanosphere samples (185.9F g-1) and Co3O4particles (68.8F g-1). Furthermore, single-shelled nanosphere samples alsodeliver excellent capacitance retention of92.8%after1000charge-dischargecycles.