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The Manganese dioxide/reduced graphene oxide (MnO2/RGO) double-shelled hollow microsphere with an improved electrical conductivity and accessible surface area has been synthesized using the monodispersive polystyrene (PS) microsphere as a self-sacrificing template. RGO/PS core–shell microsphere was prepared through p–p stacking interaction between PS microsphere and graphene oxide sheet, and then chemical reduction using hydrazine hydrate. MnO2/RGO/PS core-shell-shell microsphere was prepared through in situ chemical redox process between KMnO4 and benzyl alcohol-anchored RGO/PS. MnO2/RGO double-shelled hollow microsphere was obtained by etching PS microsphere from MnO2/RGO/PS using tetrahydrofuran. It had a pore diameter of 560–580 nm and layer thickness of 210–270 nm. Low charge transfer resistance of 0.3006 X and total electrochemical impedance of 2.37 X caused a high specific capacitance of 450.1 F g
1 at 0.2 A g
1. The capacitance retention of 81.7% after 1000 cycles indicated good cycling capability at 5 A g
1. MnO2/RGO double-shelled hollow microsphere presented the promising application for supercapacitor electrode material.

I. INTRODUCTION

Supercapacitors are regarded as a new type of energy storage devices with high power density and long lifespan. Supercapacitors are classified into electric doublelayer capacitor (EDLC) and pseudocapacitor based on the different mechanism of charge storage. Different electrode materials have been developed such as various carbons, conducting polymers, and transition metal oxides or nitrides.1–5 EDLC achieves energy store by forming a double layer of electrolyte ions on the surface of conductive porous carbon materials such as activated carbon, carbon nanotubes, and carbon aerogels.6,7 However, low energy density limits their energy-offering application. On the other hand, pseudocapacitor achieves high charge storage through reversible faradaic redox reaction between metal oxides or conducting polymers and reactive electrolytes.8–10 Manganese dioxide (MnO2) is considered as a good candidate of supercapacitor electrode material because of its electrochemical behavior, low cost, and environmental compatibility.11–13 MnO2 has a high theoretical capacitance of 1370 F g
1. Nevertheless, MnO2 does not usually deliver ideal specific capacitance because of its poor electrical conductivity and electrochemical dissolution during cycling process.14,15 To overcome these

Contributing Editor: Ian M. Reaney a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.158 J. Mater. Res., 2016

http://journals.cambridge.org

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weaknesses, carbonaceous materials with high electrical conductivity has been widely chosen as buffer matrices of MnO2 to improve the conductivity and cycling stability.15,16 Graphene is emerging as one of the most appealing carbon material because of its unique properties such as superior electrical conductivity, excellent mechanical flexibility, and high thermal and chemical stability.7,17 To improve the electri