VIETNAM NATIONAL UNIVERSITY, HANOI
VIETNAM JAPAN UNIVERSITY
NGUYEN THANH HAI
PREPARATION OF MANGANESE
DIOXIDE/GRAPHENE COMPOSITES BY
PLASMA-ENHANCED
ELECTROCHEMICAL EXFOLIATION
PROCESS AND ITS ELECTROCHEMICAL
PERFORMANCE
MASTER’S THESIS
Hanoi, 2019
i
VIETNAM NATIONAL UNIVERSITY, HANOI
VIETNAM JAPAN UNIVERSITY
NGUYEN THANH HAI
PREPARATION OF MANGANESE
DIOXIDE/GRAPHENE COMPOSITES BY
PLASMA-ENHANCED
ELECTROCHEMICAL EXFOLIATION
PROCESS AND ITS ELECTROCHEMICAL
PERFORMANCE
Major: Nanotechnology
Code: Pilot
Research supervisor:
Dr. Phan Ngoc Hong
MASTER’S THESIS
Hanoi, 2019
ii
TABLE OF CONTENTS
TITLE PAGE ............................................................................................................. i
TABLE OF CONTENTS ........................................................................................ ii
LIST OF FIGURES ................................................................................................. iv
LIST OF TABLES ................................................................................................... vi
LIST OF ABBREVIATIONS ............................................................................... vii
ACKNOWLEDGMENTS .................................................................................... viii
DECLARATION ..................................................................................................... ix
ABSTRACT ............................................................................................................... x
INTRODUCTION .................................................................................................... 1
Chapter 1 OVERVIEW ............................................................................................ 3
1.1. Electrochemical energy storages .................................................................. 3
1.1.1. Supercapacitors ...................................................................................... 5
1.2. Electrode materials for supercapacitors ..................................................... 6
1.2.1. MnO2/graphene composites ................................................................... 7
1.2.1.1. Direct oxidation-reduction reaction ................................................... 8
1.2.1.2. Solution-based mechanical mixing .................................................. 10
1.2.1.3. The other methods ........................................................................... 13
1.3. Current research in Vietnam ..................................................................... 15
Chapter 2 MATERIALS AND METHODS ......................................................... 18
2.1. Chemicals and reagents .............................................................................. 18
2.2. Preparation of MnO2/graphene composites .............................................. 18
2.3. Preparation of graphene and GM1 electrodes ......................................... 19
2.4. Preparation of symmetric supercapacitor (GM1//GM1) ......................... 20
2.5. Characterizations ........................................................................................ 20
2.6. Electrochemical analysis ............................................................................. 21
Chapter 3 RESULTS AND DISCUSSION ........................................................... 23
3.1. Characterizations of MnO2/graphene composites .................................... 23
3.2. The proposed mechanism for PE3P method ............................................. 29
3.3. Electrochemical performance .................................................................... 30
iii
3.4. Symmetric supercapacitor .......................................................................... 35
CONCLUSIONS ..................................................................................................... 39
LIST OF PUBLICATIONS ................................................................................... 40
REFERENCES ........................................................................................................ 42
iv
LIST OF FIGURES
Figure 1.1. A Ragone plot for various electrochemical energy storage devices [33]. .......... 4
Figure 1.2. The working principles of (a) electrochemical double layer capacitor (carbon
as the electrode material) and (b) Pseudocapacitor (MnO2 as the electrode material) in
Na2SO4 electrolyte [18]. ........................................................................................................ 5
Figure 1.3. (a) Schematic illustration for the synthesis of graphene–MnO2 composite (b)
the comparison of specific capacitance with other materials [48]. ........................................ 8
Figure 1.4. Schematic representations of the experimental design of MnO2/rGO composite
[53]. ........................................................................................................................................ 9
Figure 1.5. Schematic graphic of the synthesis process of the rGO/MnOx composite [41].
............................................................................................................................................. 10
Figure 1.6. The formation mechanism for GO-MnO2 nanocomposites [2]. ....................... 11
Figure 1.7. (a) Schematic representations for MnO2 anchoring on graphene through
electrostatic attraction, (b,c) TEM image and (d) capacitance retention of MnO2/graphene
[56]. ...................................................................................................................................... 12
Figure 1.8. Laser scribing of high-performance and flexible graphene/MnO2-based
electrochemical capacitors [8]. ............................................................................................ 13
Figure 1.9. (a) Schematic illustration for plasma-assisted electrochemical exfoliation
method, (b) TEM image of graphene sheets and (c) XPS of C1s in graphene samples [37]
............................................................................................................................................. 15
Figure 1.10. The detailed process of printing supercapacitor electrodes [7]. ..................... 16
Figure 2.1. The schematic representation of the experimental design. ............................... 19
Figure 3.1. SEM images of (a) graphene, (b) GM1 (1 mM KMnO4), (c) GM10 (10 mM
KMnO4) and (d) MnO2 nanoparticles (1 mM KMnO4), respectively. ................................. 23
Figure 3.2. EDX results of GM1 and their element mapping images. ................................ 24
Figure 3.3. TEM images of (a) graphene and (b) GM1. ..................................................... 25
Figure 3.4. Raman spectra of GM1 and graphene. ............................................................. 25
Figure 3.5. XRD pattern of graphene and GM1 samples. .................................................. 27
Figure 3.6. XPS patterns of GM1, (a) survey, (b) C1s, (c) O1s and (d) Mn2p. ................. 28
Figure 3.7. Proposed mechanism for the formation of graphene/MnO2 composite ........... 29
Figure 3.8. Cyclic voltammetry curves of (a) graphene and (b) GM1 electrodes in a 6 M
KOH electrolyte at a different scan rate of 5, 10, 20, 50, 100 mV s-1. ................................ 31