Abstract

Porous MnO2 was uniformly electrodeposited on nickel foam in MnSO4 solution, which was applied as the electrode of supercapacitors. The nucleation/growth mechanisms of porous MnO2 were investigated firstly. Then two kinds of electrochemical measuring technologies, corresponding to the cycle voltammetry (CV) and galvanostatic charge-discharge, were adopted to assess the electrochemical performance of MnO2 electrodes. The results demonstrated that the deposition of MnO2 on nickel foam included four stages. Prior to the deposition, an extremely short incubation period of about 2 s was observed (the first stage). Then the exposed nickel foam was instantly covered by a large number of MnO2 crystal nuclei and crystal nuclei connected with each other in a very short time of about 3 s (the second stage). Nucleation predominated in the second stage. The sharply rise of current was caused by the increase in substrate surface area which due to nucleation of MnO2. Grain boundaries grew preferentially due to their high energy, accompanied with a honeycomb-like structure with the higher surface area was formed. However, accompanied with the electrochemical reactions gradually diffusion-controlled, the current presented the decline trend with increasing the time (the third stage). When the electrochemical reactions were completely diffusion-controlled, the porous MnO2 coating with an approximately constant surface area was formed (the fourth stage). MnO2 coatings deposited for different time (30, 60, 120, 300 s) exhibited a similar specific capacitance (CV: about 224 F/g; galvanostatic charge-discharge: about 264 F/g). Comparatively speaking, the value of MnO2 deposited for 600 s was highest (CV: 270 F/g; galvanostatic charge-discharge: 400 F/g).

Highlights

  • The ever-increasing demands for clean and renewable energy and growing awareness of the environmental protection promote the development of efficient energy storage and energy conversion equipment [1,2,3,4]

  • MnO2 coatings deposited for different time (30, 60, 120, 300 s) exhibited a similar specific capacitance (CV: about 224 F/g; galvanostatic charge-discharge: about 264 F/g)

  • Speaking, the value of MnO2 deposited for 600 s was highest (CV: 270 F/g; galvanostatic charge-discharge: 400 F/g)

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Summary

Introduction

The ever-increasing demands for clean and renewable energy and growing awareness of the environmental protection promote the development of efficient energy storage and energy conversion equipment [1,2,3,4]. Electrodeposition can be directly employed to prepare the electrode by MnO2 deposition on different substrates. The current investigations on MnO2 electrodeposition on nickel foam primarily focus on the influence of electrode preparation on the electrochemical performance of electrodes. A limited number of studies reported the nucleation/growth mechanisms of MnO2 electrodeposition on nickel foam. Theoretical studies on nucleation and growth mechanisms remain essential Such studies offer guidance for obtaining MnO2 electrodes with excellent electrochemical performance. Morphological evolution of MnO2 deposited at different time (3, 7, 20, 40 and 120 s) was analyzed to confirm its nucleation and growth mechanisms in detail. The MnO2 electrodes prepared at different time periods (30, 60, 120, 300 and 600 s) were used for electrochemical performance testing. The electrochemical properties of MnO2 deposited for different time was evaluated in Na2 SO4 by two kinds of electrochemical measuring technologies (cyclic voltammertry (CV) and galvanostatic charge-discharge)

Experimental
Formation Process of MnO2
This inconsistency may be to 2 formed
Chemical Compositions and Phase Constituents of the Deposit
Morphological Evolution of MnO22
Evaluation of Electrochemical Performance
The mass of 2deposited
13. CV curves taken taken from from nickel nickel foam and MnO
14. Galvanostatic
(Figures
Conclusions
Full Text
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