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Nucleation/Growth Mechanisms and Morphological Evolution of Porous MnO2 Coating Deposited on Graphite for Supercapacitor

School of Materials Engineering, Shanghai University of Engineering Science, Shanghai 201620, China
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Materials 2017, 10(10), 1205; https://doi.org/10.3390/ma10101205
Received: 6 September 2017 / Revised: 9 October 2017 / Accepted: 16 October 2017 / Published: 19 October 2017
The nucleation and growth mechanisms of porous MnO2 coating deposited on graphite in MnSO4 solution were investigated in detail by cyclic voltammetry, chronoamperometry and scanning electron microscopy. The electrochemical properties of honeycomb-like MnO2 were evaluated by cycle voltammetry and galvanostatic charge-discharge. Results indicated that MnO2 was synthesized by the following steps: Mn2+ Mn3++ e-, Mn3++2H2O → MnOOH + 3H+, and MnOOHMnO2 + H++ e-. The deposition of MnO2 was divided into four stages. A short incubation period (approximately 1.5 s) was observed, prior to nucleation. The decreasing trend of the current slowed as time increased due to nucleation and MnO2 growth in the second stage. A huge number of nuclei were formed by instantaneous nucleation, and these nuclei grew and connected with one another at an exceedingly short time (0.5 s). In the third stage, the gaps in-between initial graphite flakes were filled with MnO2 until the morphology of the flakes gradually became similar to that of the MnO2-deposited layer. In the fourth stage, the graphite electrode was covered completely with a thick and dense layer of MnO2 deposits. All MnO2 electrodes at different deposition times obtained nearly the same specific capacitance of approximately 186 F/g, thus indicating that the specific capacitance of the electrodes is not related with deposition time. View Full-Text
Keywords: MnO2; coating; electrodeposition; nucleation and growth; morphological evolution MnO2; coating; electrodeposition; nucleation and growth; morphological evolution
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Huang, W.; Li, J.; Xu, Y. Nucleation/Growth Mechanisms and Morphological Evolution of Porous MnO2 Coating Deposited on Graphite for Supercapacitor. Materials 2017, 10, 1205.

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