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Issue 35, 2019
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Phase and morphology controlled polymorphic MnO2 nanostructures for electrochemical energy storage

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Abstract

In this work, a series of MnO2 nanostructures with different crystallographic structures, including δ-MnO2 nanotubes and α-MnO2 nanorods, were prepared using polycarbonate membrane as a template. The crystallographic structure and morphology were controlled by adjusting the pH of the KMnO4 solutions via a one-step hydrothermal method. The crystal form of the samples changed from birnessite to α-MnO2 with the decrease in the applied pH values and a precise pH value for the critical point was found. When used as positive electrode materials in the supercapacitor, the structure prepared in the higher pH value solutions (MnO2-12, pH = 12) with a δ-type crystallographic structure gave an ideal specific capacitance of 364.1 F g−1 at a current density of 0.5 A g−1, a good rate capability, and a favorable cycling stability. An asymmetric supercapacitor assembled with MnO2-12 as the positive electrode and activated graphene (AG) as the negative electrode produced an energy density of 29.4 W h kg−1 at a power density of 248.9 W kg−1. The excellent electrochemical properties were attributed to the novel tubular structure composed of poor crystalline δ-MnO2 nanosheets, resulting in a high ionic conductivity and two-sided reaction surfaces.

Graphical abstract: Phase and morphology controlled polymorphic MnO2 nanostructures for electrochemical energy storage

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Supplementary files

Article information


Submitted
04 Jun 2019
Accepted
30 Jul 2019
First published
30 Jul 2019

CrystEngComm, 2019,21, 5322-5331
Article type
Paper

Phase and morphology controlled polymorphic MnO2 nanostructures for electrochemical energy storage

M. Shen, S. J. Zhu, X. Liu, X. Fu, W. C. Huo, X. L. Liu, Y. X. Chen, Q. Y. Shan, H. Yao and Y. X. Zhang, CrystEngComm, 2019, 21, 5322
DOI: 10.1039/C9CE00865A

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