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4266802 
Journal Article 
Enhanced Cycleability of Amorphous MnO₂ by Covering on α-MnO₂ Needles in an Electrochemical Capacitor 
Liu, Q; Ji, S; Yang, J; Wang, H; Pollet, BG; Wang, R 
2017 
1 
Materials
ISSN: 1996-1944 
10 
9 
English 
28837099 
WOS:000411506700008 
An allomorph MnO₂@MnO₂ core-shell nanostructure was developed via a two-step aqueous reaction method. The data analysis of Scanning Electron Microscopy, Transmission Electron Microscopy, X-Ray Diffraction and N₂ adsorption-desorption isotherms experiments indicated that this unique architecture consisted of a porous layer of amorphous-MnO₂ nano-sheets which were well grown onto the surface of α-MnO₂ nano-needles. Cyclic voltammetry experiments revealed that the double-layer charging and Faradaicpseudo-capacity of the MnO₂@MnO₂ capacitor electrode contributed to a specific capacitance of 150.3 F·g-1at a current density of 0.1 A·g-1. Long cycle life experiments on the as-prepared MnO₂@MnO₂ sample showed nearly a 99.3% retention after 5000 cycles at a current density of 2 A·g-1. This retention value was found to be significantly higher than those reported for amorphous MnO₂-based capacitor electrodes. It was also found that the remarkable cycleability of the MnO₂@MnO₂ was due to the supporting role of α-MnO₂ nano-needle core and the outer amorphous MnO₂ layer.