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Issue 2, 2016
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Hierarchical three-dimensional mesoporous MnO2 nanostructures for high performance aqueous asymmetric supercapacitors

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Abstract

We describe a new facile chemical route for the synthesis of hierarchical mesoporous α-MnO2 and the development of an aqueous asymmetric supercapacitor. The hierarchical α-MnO2 is synthesized by the thermodynamically favorable redox reaction between metallic Zn and MnO4 in mild acidic solutions without any template. Zn and the in situ generated nascent hydrogen efficiently reduce MnO4 to MnO2. The growth mechanism is studied with time-dependent electron microscopic measurements. The α-MnO2 has a three-dimensional (3D) flower-like mesoporous hierarchical structure with an average size of 500 nm and a large surface area (206 m2 g−1) with a pore size of 48.34 Å and a pore volume of 0.543 cm3 g−1. It has significantly high electronic conductivity with respect to traditional/commercial MnO2. A specific capacitance as high as 322 F g−1 at a current density of 1 A g−1 with excellent cycling stability (90% after 8000 cycles) is achieved. An aqueous asymmetric supercapacitor (ASC) is developed by pairing α-MnO2 and reduced graphene oxide-based electrodes. An ASC could deliver a specific capacitance of 63.5 F g−1 at 2 A g−1 with a potential window of 0–2 V. The ASC retains 100% initial specific capacitance even after 3000 continuous charge–discharge cycles. It has an energy density of 35.28 W h kg−1 at a power density of 2.0 kW kg−1 and could retain 27.78 W h kg−1 at a power density of 16.67 kW kg−1. The three-dimensional mesoporous structure favors the facilitated transport of the electrolyte across the electrode. The post-mortem XRD analysis shows that the MnO2 nanostructure retains its initial α phase even after 3000 charge–discharge cycles, though a partial disintegration of the hierarchical structure was observed.

Graphical abstract: Hierarchical three-dimensional mesoporous MnO2 nanostructures for high performance aqueous asymmetric supercapacitors

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Publication details

The article was received on 20 Oct 2015, accepted on 19 Nov 2015 and first published on 20 Nov 2015


Article type: Paper
DOI: 10.1039/C5TA08426A
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J. Mater. Chem. A, 2016,4, 587-595

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    Hierarchical three-dimensional mesoporous MnO2 nanostructures for high performance aqueous asymmetric supercapacitors

    S. Bag and C. R. Raj, J. Mater. Chem. A, 2016, 4, 587
    DOI: 10.1039/C5TA08426A

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