Rational construction of bowl-like MnO₂ nanosheets with excellent electrochemical performance for supercapacitor electrodes

Rational construction of unique hierarchical nanostructured electrodes with excellent electrochemical performance is a promising solution to satisfy the increasing demand of supercapacitors with high energy density. In this work, a novel nanostructure of bowl-like MnO₂ nanosheets with ultra-thin thickness (about 4 nm) has been successfully designed by a simple template-assisted hydrothermal method. The composition and morphology of the obtained bowl-like nanostructures have been characterized by FESEM, TEM, XRD, XPS and N₂ adsorption-desorption. Such novel nanostructures present several advantages, such as large surface area, compact contacts, reduced interior space, additional electroactive sites for reversible redox reactions and short/unimpeded diffusion channels for ions/electron transport. When evaluated as electrode materials, bowl-like MnO₂ nanosheets exhibit a specific capacitance of 379 F g⁻¹ at a current density of 0.5 A g⁻¹, a capacitance retained ratio of 60.5% from 0.5 to 10 A g⁻¹ and 87.3% capacitance retention after 5000 cycles. Moreover, a possible mechanism for the excellent electrochemical performance of the novel bowl-like nanostructures compared with hollow particles has been systematically studied. We believe that this strategy can open up an avenue and appropriate idea for the rational construction of other transition metal oxides with high performance for the practical supercapacitor applications.