MnO₂ nanorods/SiO₂ sphere coated on single-wall carbon nanotubes as supercapacitor electrode for high energy storage applications

A composite of MnO₂/SiO₂ sphere was coated on single-wall carbon nanotubes (MnO₂/SiO₂/SWCNT) using one-pot hydrothermal synthesis method. KMnO₄ was used as an oxidizing agent for mild functionalization of single-wall carbon nanotubes (SWCNT), and also as a precursor of MnO₂. A comparative study in the presence of SiO₂ and SWCNT was carried out using bare MnO₂ as a reference. After addition of SiO₂, the composite obtained showed an increase in both the specific capacitance and cycle life which can be associated with spherical shape of SiO₂ which offered reduction sites for MnO₂. With the addition of SWCNT less than 5%, the composite further showed an increase in capacitance and cycle life, this is because of the good conductive nature, excellent mechanical property and chemical stability of SWCNT. The electrochemical behaviour was studied using cyclic voltammetry and galvanostatic charge/discharge method in 1 M Na₂SO₄ electrolyte. The specific capacitance of MnO₂, MnO₂/SiO₂ and MnO₂/SiO₂/SWCNT composite is 73.6 F g⁻¹, 108.7 F g⁻¹ and 136 F g⁻¹ at a current density of 1 A g⁻¹, respectively. The MnO₂/SiO₂/SWCNT energy density was 68 Wh kg⁻¹ with power density of 444.4 W kg⁻¹. The MnO₂/SiO₂/SWCNT composite retained 88% of its specific capacitance after 500 cycles. We envisage that this hybrid material could be applied for preparation of supercapacitor electrode. (paper)