DEPOSITION AND OPTIMIZATION OF NANOPARTICULATE

MANGANESE DIOXIDE THIN FILMS FOR ELECTROCHEMICAL

APPLICATIONS

Awangku Nabil Syafiq Bin Awangku Metosen

Master of Science

(Physical Chemistry)

2014

Faculty of Resource Science and Technology

DEPOSITION AND OPTIMIZATION OF NANOPARTICULATE

MANGANESE DIOXIDE THIN FILMS FOR ELECTROCHEMICAL

APPLICATIONS

AWANGKU NABIL SYAFIQ BIN AWANGKU METOSEN

A thesis submitted

in fulfillment of the requirements for the degree of

Master of Science

Faculty of Resource Science and Technology

UNIVERSITY MALAYSIA SARAWAK

2014

DECLARATION

No portion of the work referred to in this dissertation has been submitted in support of an

application for another master of qualification of this or any other university/institution of

higher learning.

…………………………………………………

Awangku Nabil Syafiq Bin Awangku Metosen (11021700)

Department of Chemistry (Physical Chemistry)

Faculty of Resource Science and Technology

Universiti Malaysia Sarawak

i

ACKNOWLEDGEMENT

First of all, I would like to express my special gratitude especially to my supervisor

Professor Dr. Pang Suh Cem, who have well-guided and advised me during these tremendous

years. I would like to thank you for your countless effort and time you have spent on my

research. Your guidance has motivated me so much throughout my study. Without your endless

support, I would not be able to conduct and complete my research successfully. My sincere thank

also goes to Dr. Chin Suk Fun who acts as my co-supervisor and for giving useful suggestions

and comments whenever I needed during my research activities. Not to forget, I would also like

to thank Madam Ting Woei and Mr. Syafri for their assistance in the process of taking the TEM

and SEM micrographs of my samples.

I would also like to express my appreciation to my lovely parents, spouse, daughter and

friends for all the continuous supports and sacrifices that you all have made on my behalf during

my master study period. With all your helps, I managed to strive for my goal. Once again, I

would like to thank all of you for everything and I am grateful for what you have contributed for

me.

ii

Deposition and Optimization of Nanoparticulate Manganese Dioxide Thin Films for

Electrochemical Applications

ABSTRACT

The deposition and optimization of nanoparticulate manganese dioxide (MnO2) thin films

as electrode material for the fabrication of electrochemical capacitors have received increasing

attention among researchers worldwide. Among major issues that need to be addressed include,

microstructural optimization of MnO2 thin films in order to enhance their specific capacitance,

and the development of efficient and effective approaches for the fabrication of MnO2 thin film

electrochemical capacitors. In this study, we have investigated the influence of deposition

parameters such as MnO2 sol pH, sol concentration and addition of different type of surfactants

using the self-assembly horizontal submersion approach. The surface morphologies and

microstructure of MnO2 thin films were optimized by varying these deposition parameters. The

electrochemical properties of MnO2 thin films were enhanced through microstructural control of

nanoparticulate thin films deposited on electrically conductive supporting substrate. Besides

nickel sputtered polyethylene terephthalate (PET) substrate, conductive layers of CuS and nickel

were deposited sequentially on PET by chemical bath deposition and electrodeposition processes.

Nanoparticulate MnO2 thin film was subsequently deposited on the conductive Ni/CuS/PET

supporting substrate. Nanostructured multilayer MnO2/Ni/CuS composite films on PET

supporting substrate exhibited satisfactory capacitive behaviors in mild aqueous Na2SO4

electrolyte. In addition, nanoparticulate MnO2 thin films were deposited on nickel sputtered PET

substrates using the electrophoretic deposition (EPD) process. Deposition parameters such as

deposition potential, deposition duration and addition of dispersant agents were optimized to

enhance the electrochemical properties of MnO2 thin films. The capacitive behaviors of

nanoparticulate MnO2 thin films deposited on both Ni/CuS coated and nickel sputtered PET

iii

supporting substrates were evaluated as electrode materials for the fabrication of thin film

electrochemical capacitors.

iv

Pemendapan dan Pengoptimuman Partikel Nano Mangan Dioksida Filem Nipis untuk

Aplikasi Elektrokimia

ABSTRAK

Pemendapan dan pengoptimuman partikel nano mangan dioksida (MnO2) filem nipis

sebagai bahan elektrod untuk fabrikasi kapasitor elektrokimia telah menerima perhatian

meningkat di kalangan penyelidik di seluruh dunia. Antara isu-isu utama yang perlu ditangani

termasuk, pengoptimuman mikrostruktur daripada MnO2 filem nipis bagi meningkatkan

kapasitan spesifik mereka, serta pembangunan yang cekap dan pendekatan berkesan untuk

fabrikasi MnO2 filem nipis kapasitor elektrokimia. Dalam kajian ini, kami telah mengkaji

pengaruh parameter pemendapan seperti pH sol MnO2 , kepekatan sol MnO2 dan penambahan

surfaktan yang berlainan jenis menggunakan pendekatan pemasangan sendiri penenggelaman

mendatar. Morfologi permukaan dan struktur mikro filem nipis MnO2 dioptimumkan dengan

mengubah parameter pemendapan. Sifat-sifat elektrokimia filem nipis MnO2 telah

dipertingkatkan melalui kawalan mikrostruktur daripada partikel nano filem nipis disimpan di

substrat sokongan elektrik konduktif. Selain substrat polietilena terephthalate (PET) diselaputi

nikel, lapisan konduktif Cus dan nikel yang dimendap secara berurutan pada PET melalui proses

pemendapan dalam larutan kimia dan pengelektroenapan. Partikel nano MnO2 filem nipis

kemudiannya dienapkan di atas substrat sokongan konduktif Ni/CuS/PET. Struktur nano lapisan

filem komposit MnO2/Ni/CuS pada substrat PET menunjukkan prestasi yang memberangsangkan

di dalam elektrolit akueus Na2SO4. Di samping itu, partikel nano MnO2 filem nipis dienapkan

pada substrat PET yang deselaputi nikel menggunakan proses pemendapan elektroforetik (EPD).

Faktor pemendapan seperti potensi pemendapan, tempoh pemendapan dan penambahan ejen

dispersan telah dioptimumkan untuk meningkatkan ciri-ciri elektrokimia filem nipis MnO2.

Tingkah laku kapasitif partikel nano MnO2 filem nipis yang dienapkan pada kedua-dua Ni/Cus

v

dan nikel bersalut PET substrat sokongan telah dinilai sebagai bahan elektrod untuk fabrikasi

kapasitor elektrokimia filem nipis.

vi

TABLE OF CONTENTS

Page

Acknowledgements i

Abstract ii

Abstrak iv

Table of Contents vi

List of Tables xi

List of Figures xi

List Abbreviations xv

List of Symbols xvi

CHAPTER 1 INTRODUCTION

1.1 Background 1

1.2 Objectives 6

1.3 Goals and Findings 6

CHAPTER 2 LITERATURE REVIEW

2.1 Preparation of Stable Metal Oxides Colloidal Suspensions 9

2.2 Manganese Dioxide Thin Films as Electrode Material of Electrochemical

Capacitors (EC)

12

2.3 Factors Influencing Electrochemical Properties of Manganese Dioxide

Thin Films

15

2.4 Deposition of Copper Sulfide and Nickel Films onto Polymer Surfaces 17

2.5 Electrophoretic Deposition of Manganese Dioxide Thin Films 20

vii

CHAPTER 3 DEPOSITION AND OPTIMIZATION OF MANGANESE

DIOXIDE THIN FILMS VIA A SELF-ASSEMBLY HORIZONTAL

SUBMERSSION PROCESS

3.1 Introduction 25

3.2 Materials and Methods

3.2.1 Materials 27

3.2.2 Pretreatment of Stainless Steel Substrate 27

3.2.3 Preparation of Manganese Dioxide Colloidal Suspension (Sol) 27

3.2.4 Optimization of MnO2 Thin Film Deposited via Self-Assembly

Process

3.2.4.1 Effect of MnO2 Colloidal Suspension (Sol)

Concentration

28

3.2.4.2 Effect of Sol pH 28

3.2.4.3 Effect of Surfactant 29

3.2.5 Deposition of MnO2 Thin Film 29

3.2.6 Characterization of Manganese Dioxide Thin Film 29

3.3 Results and Discussion

3.3.1 Morphological Characterization of Manganese Dioxide

Nanoparticles and Thin Films

31

3.3.1.1 Effect of MnO2 Sol Concentrations 31

3.3.1.2 Effect of Sol pH 34

3.3.1.3 Effect of Surfactants 40

3.3.2 Electrochemical Characterization of Manganese Dioxide Thin 45

viii

Films

3.3.2.1 Effect of Sol Concentrations 45

3.3.2.2 Effect of Sol pH 47

3.3.2.3 Effect of Surfactants 49

3.3.2.4 Effect of CTAB Surfactant Concentrations 51

3.4 Conclusion 54

CHAPTER 4 DEPOSITION AND OPTIMIZATION OF MULTILAYER

MnO2/Ni/CuS COMPOSITE FILMS ON POLYETHYLENE

TEREPHTHALATE (PET) SUPPORTING SUBSTRATE

4.1 Introduction 55

4.2 Materials and Methods

4.2.1 Chemical Deposition of Copper Sulfide (CuS) Film on PET

Substrate

57

4.2.2 Electrodeposition of Nickel Film onto CuS/PET Substrate 57

4.2.3 Deposition of MnO2 Thin Film on Ni/CuS/PET Substrate 58

4.2.4 Characterization of CuS/PET, Ni/CuS/PET and

MnO2/Ni/CuS/PET

59

4.3 Results and Discussion

4.3.1 Deposition of Copper Sulfide (CuS) on PET Film 60

4.3.1.1 Effect of Copper Sulfide Film Thickness 61

4.3.2 Electrodeposition of Nickel Film on CuS/PET 65

4.3.2.1 Effect of Electrodeposition Duration 68

4.3.2.2 Effect of Agitation Mode 71

ix

4.3.3 Effect of Post Deposition Annealing Temperatures 74

4.3.4 Effect of Surfactant on Electrodeposited Nickel Film 77

4.3.5 Characterization of MnO2/Ni/CuS/PET Composite Film 81

4.3.6 Fabrication and Characterization of Electrochemical Capacitor

Prototype

83

4.3.6.1 Cycling Stability of Electrochemical Capacitor

Prototype

84

4.4 Conclusion 86

CHAPTER 5 DEPOSITION AND OPTIMIZATION OF MANGANESE

DIOXIDE THIN FILMS VIA ELECTROPHORETIC

DEPOSITION PROCESS

5.1 Introduction 87

5.2 Materials and Methods 89

5.3 Results and Discussion

5.3.1 Effect of Deposition Voltage 91

5.3.2 Effect of Deposition Duration 94

5.3.3 Effect of Dispersant Agents 98

5.3.4 Electrochemical Cycling Stability 106

5.4 Conclusion 114

CHAPTER 6 CONCLUSION AND RECOMMENDATIONS

6.1 Concluding Remarks 115

x

6.2 Recommendations for Future Works 117

CHAPTER 7 REFERENCES 119

xi

List of Tables Page

Table 3.1 Concentrations of MnO2 sols prepared 28

List of Figures Page

Figure 2.0 (a) MnO6 octahedron. (b) Crystal structures of MnO2 polymorphs

showing the connections of MnO6 octahedra.

13

Figure 2.1 Schematic diagram of Electrophoretic Deposition Process 21

Figure 3.1 SEM micrographs of MnO2 thin film deposited from MnO2 sols of

concentrations: a) 0.010 M, b) 0.0050 M, c) 0.0030 M, d) 0.0010 M,

and e) 0.0005 M.

32

Figure 3.2 TEM micrographs of MnO2 thin films deposited from MnO2 sol of

concentration: a) 0.010 M, b) 0.005 M, c) 0.003 M and d) 0.001 M.

34

Figure 3.3 SEM micrographs of MnO2 thin films deposited from acidic and

alkaline sols: a) pH 1.34, b) pH 2.45, c) pH 3.42, d) pH 7.62, e) pH

8.60, and f) pH 11.68.

37

Figure 3.4 TEM micrographs of dispersed MnO2 thin films deposited from MnO2

sols of different pH values: a) pH 2.45, b) pH 3.42, c) pH 8.60, and d)

pH 11.68.

38

Figure 3.5 Mass loading of MnO2 thin films deposited from MnO2 sol of different

pH values.

40

Figure 3.6 SEM micrographs of MnO2 thin films formed in the presence of

different surfactants without heating and heated at 200˚C: a) CTAB, b)

CTAB (heated), c) SDS, d) SDS (heated), e) Brij-35, and f) Brij-35

(heated).

42

Figure 3.7 SEM micrographs of MnO2 films deposited in the presence of different

CTAB surfactant concentrations: a) 0.0 M, b) 0.005 M, and c) 0.10 M.

43

Figure 3.8 Mass loading of MnO2 thin films deposited in the presence of different

CTAB concentrations in MnO2 sol.

44

Figure 3.9 (a) Cyclic voltammograms of the MnO2 thin films deposited at different

MnO2 sol concentrations, and (b) Effect of MnO2 sol concentration on

the specific capacitance (mF/cm²) of deposited MnO2 thin films.

46

Figure 3.10 (a) Cyclic voltammograms of MnO2 thin film deposited from sol of

different pH values and (b) Effects of sol pH on the specific capacitance

(mF/cm²) of MnO2 thin films.

48

Figure 3.11 (a) Cyclic voltammograms of MnO2 thin films deposited in the presence 50

xii

of different surfactants and heat treated in air at 200 ˚C, and (b) Effect

of different surfactants and heat treatment on the specific capacitance of

MnO2 thin films.

Figure 3.12 Cyclic voltammograms of MnO2 thin films deposited in the presence of

different concentrations of CTAB, (b) Effect of CTAB concentration on

the mass loading and specific capacitance of MnO2 thin films.

53

Figure 4.1 EDX spectrum of copper sulfide (CuS) on PEI treated PET film. 60

Figure 4.2 Color photograph of PEI-treated film before deposition and after

deposition of CuS films with different number of coatings.

62

Figure 4.3 SEM micrographs of PET substrate deposited with CuS film after

various numbers of coating with chemical bath deposition. (a) 0, (b) 1,

(c) 2, (d) 3, and (e) 4. Inset shows individual particles of CuS on the

film.

63

Figure 4.4 Relative surface resistance (ohms per square) of PET substrate coated

with different layers of copper sulfide film.

64

Figure 4.5 SEM micrographs of nickel films electrodeposited under different

applied potential: (a) 2.0 V, (b) 2.5 V, and (c) 3.0 V.

66

Figure 4.6 Relative surface resistance (ohms per square) of nickel electrodeposited

under different applied potential at a fixed deposition duration of 20

minutes.

67

Figure 4.7 SEM micrographs of nickel films electrodeposited under different

duration: (a) 5 minutes, (b) 10 minutes, (c) 15 minutes, (d) 20 minutes,

and (e) 25 minutes.

69

Figure 4.8 Relative surface resistance (ohms per square) of nickel deposited at

various duration at a fixed applied potential of 2.0 V.

70

Figure 4.9 Relative surface resistance of nickel films deposited under different

agitation modes: a) Without agitation, b) Magnetic stirring, and c)

Ultrasonication.

72

Figure 4.10 SEM micrographs of nickel films deposited under different agitation

modes: a) Without agitation, b) Magnetic stirring, and c)

Ultrasonication.

73

Figure 4.11 SEM micrographs of Ni (a-d) and CuS (e-f) films annealed at different

temperatures. (a) 50 ˚C, (b) 100 ˚C, (c) 150 ˚C, (d) 200 ˚C, (e) CuS

(without heating) and (f) CuS (heated at 150 ˚C).

75

Figure 4.12 Effect of annealing temperatures on the relative surface resistance of

both nickel and copper sulfide films.

77

xiii

Figure 4.13 SEM micrographs of nickel film deposited in the presence of different

concentration of SDS surfactant. (a) Without SDS, (b) 0.5 g/L SDS, (c)

1.0 g/L SDS, (d) 1.5 g/L SDS; and (e) 2.0 g/L SDS.

79

Figure 4.14

Surface resistance of nickel films electrodeposited with different SDS

concentrations.

81

Figure 4.15

Figure 4.16

Figure 4.17

(a) SEM and (b) TEM micrographs of MnO2 thin film deposited onto

the Ni/CuS/PET substrate.

Cyclic voltammogram of electrochemical capacitor prototype fabricated

from the multilayers of MnO2/Ni/CuS/PET composite film.

Cyclic voltammogram of electrochemical capacitor prototype fabricated

from the multilayers of MnO2/Ni/CuS/PET composite film.

82

83

85

Figure 5.1 SEM micrographs of MnO2 films electrophoretic deposited at the

applied voltage of (a) 1.0 V and (b) 2.0 V.

92

Figure 5.2

(a) Cyclic voltammograms of EC prototypes with MnO2 thin films

deposited at different applied potentials, and (b) Effect of applied

potentials on specific capacitances (mF/cm²) of EPD MnO2 films.

93

Figure 5.3 MnO2 films deposited at a duration of (a) 5 minutes, (b) 25 minutes, and

(c) 30 minutes under constant applied potential of 2.0 V.

95

Figure 5.4 (a) Cyclic voltammogramms of EC prototypes with MnO2 thin films

deposited at various deposition durations, and (b) Specific capacitance

(mF/cm²) of the MnO2 films deposited at variable durations.

97

Figure 5.5 MnO2 films deposited in the presence of different types of dispersant

agents (sodium alginate: 5a - 5c; sodium tripolyphosphate: 5d – 5f) at

different concentrations (0.5 g/L: 5a and d; 1.0 g/L: 5b and e; 2.5 g/L:

5c and f). Insets of Figures 5b and 5e show TEM micrographs of MnO2

nanoparticles.

101

Figure 5.6 (a) Cyclic voltammograms of EC prototypes with MnO2 thin films

deposited in the presence of different concentrations of (a) sodium

alginate, and (b) sodium tripolyphosphate.

105

Figure 5.7 Comparison of charge capacity (mF/cm²) of EC prototypes with MnO2

films deposited in the presence of different dispersant agents at various

concentrations. (a) Sodium tripolyphosphate, and (b) sodium alginate.

106

Figure 5.8 Capacitive behaviors of EC prototypes with MnO2 thin film in 0.2 M

Na2SO4 aqueous solution. (a) cyclic voltammograms at various cycles,

and (b) variation of specific capacitances with number of cycles.

108

Figure 5.9 SEM micrograph of MnO2 films a) before cycling, and after cycling for

(b) 250 cycles, and c) 2500 cycles.

110

xiv

Figure 5.10 Cyclic voltammogram of EC prototypes with MnO2 thin film deposited

on Ni/CuS/PET supporting substrate at various cycles.

112

Figure 5.11 Comparison of specific capacitance (mF/cm²) of EC prototypes with

MnO2 thin films deposited on Ni/CuS/PET and sputtered-Ni/PET

substrates.

112

Figure 5.12

SEM micrographs of MnO2 film deposited on Ni/CuS/PET substrate: a)

before cycling, and b) after cycling for 2500 cycles.

113

xv

List of Abbreviations

AAS Atomic Absorption Spectrophotometer

ABS Acrylonitrile Butadiene Styrene

CMC Critical Micellar Concentration

CTAB Cetyl Trimethylammonium Bromide

CV Cyclic Voltammetry

DC Direct Current

EC Electrochemical Capacitor

ECD Electrochemical Deposition

EDLC Electrochemical Double Layer Capacitor

EDX Energy Dispersive X-Ray

EPD Electrophoretic Deposition

MWCNT Multiwalled Carbon Nanotube

PEI Polyethyleneimine

PET Polyethylene Terephthalate

SC Specific Capacitance

SCE Saturated Calomel Electrode

SDS Sodium Dodecyl Sulphate

SEM Scanning Electron Microscope

TEM Transmission Electron Microscope

xvi

List of Symbols

dm3 Cubic decimeter

C Capacitance

q Charge

V Voltage difference between plates

F/g Farad per gram

% Percentage

> Higher than

cm2 Centimeter square

mF/cm2 Millifarad per centimeter square

˚C Degree Celsius

β Beta

mg/cm2 Milligram per centimeter square

F/cm2 Farad per centimeter square

mV/s Millivolt per second

V Voltage

mm millimeter

mL milliliter

M Molarity

g/mol Gram per mole

mA Milliampere

g/L Gram per liter

kHz Kilohertz

nm Nanometer

Ω/square Ohm per square

1

CHAPTER 1

INTRODUCTION

1.1 Background

The rapid development of our society has aggravated environmental pollution and

escalated depletion of fossil fuels. There is a pressing need for research and development on more

environmental friendly and sustainable sources of energy as well as novel materials and

technologies associated with energy conversion and storage. The importance of nanostructured

thin-film materials for energy conversion and storage have resulted in a tremendous increase of

innovative thin-film processing technologies in recent years. Currently, this development goes

hand-in-hand with the explosion of scientific and technological breakthroughs in

microelectronics, optics and nanotechnology. Thin-film process technologies for films of

thicknesses ranging from one to several microns are essential for a multitude of applications such

as thermal barrier coatings and wear protections, enhancing service life of tools and to protect

materials against thermal and atmospheric influences (Lokhande et al., 2009).

Batteries and electrochemical capacitors represents the current state of the art of energy

storage technologies for storing kinetic, potential, chemical, magnetic, or thermo-chemical

energy. Batteries and low temperature fuel cells are some typical low power devices. In contrast,

electrochemical capacitors possess high power density but low energy density. Henceforth, a

combination of battery and electrochemical capacitor is expected to enhance the overall

performance in terms of power density and energy density. In addition, electrochemical

capacitors have a much longer cycle life than batteries because negligible chemical charge

2

transfer reactions are involved (Conway et al., 1997; Kötz and Carlen, 2000; Dario and Kötz,

2012; Deng et al., 2013).

Based on the current research and development trends, electrochemical capacitors can be

divided into three general classes, namely electrical-double layer capacitors, pseudocapacitors,

and hybrid capacitors with each class having its own unique individual characteristic mechanism

for storing charge, which are non-faradaic, faradaic, and a combination of the two, respectively.

Faradaic processes such as oxidation and reduction reactions involve the transfer of charge

between electrode and electrolyte. Hence, pseudo-capacitive electrochemical capacitors functions

based on the charge storage brought about by the fast and reversible redox reaction near the

surface of electroactive material (Shukla et al., 2012; Deng et al., 2013). Electrochemical

capacitor can be charged and discharged quickly like a capacitor, but it exhibits 20–200 times

greater capacitance than conventional capacitors. The higher capability of electrochemical

capacitor comes from the electrostatic storage of charge at the electrode surface. The transport of

ions in the electrolyte to the electrode surface is rapid, leading to fast charge and discharge

capability. The charging and discharging processes are highly reversible and do not require phase

changes in the electrodes. This, logically, also leads to increased cycle life compared to batteries

(Chu and Braatz, 2002). Electrochemical capacitor basically consists of two symmetrical

electrodes arranged in parallel or in array, separated by an aqueous or non-aqueous electrolyte

either in liquid or solid form that stores electrical energy at the electrode/electrolyte interface

(Kötz and Carlen, 2000; Choudhury et al., 2009).

Metal oxides present attractive alternatives as electrode materials due to their high

specific capacitance and comparatively low resistance, and hence their potential utility in

3

fabricating electrochemical capacitors of high energy and power density. Notably, ruthenium

dioxide (RuO2) has been known to exhibit very high specific capacitance which ranges from 720

F/g to 900 F/g. However, its high cost and scarcity have rendered its utilization for the fabrication

of electrochemical devices not economically feasible. As such, researchers have diverted their

attention towards other transition metal oxides including MnO2, NiO, Ni(OH)2, Co2O3, IrO2,

FeO, TiO2, SnO2, V2O5, and MoO (Jayalakshmi and Balasubramanian, 2008). Manganese oxide

is of particular interest because of its various potential applications, for instance, in

electrochemical, electrochromic, and fuel cell devices, (Ul Islam et al., 2005), as catalyst for a

wide range of industrial catalytic applications (Luo, 2007), molecular sieves, sensors (Umek et

al., 2011), ion-exchangers and selective adsorption materials of radio nuclides (Unuma et al.,

2003). Manganese dioxide (MnO2) is one of the most widely used and promising

pseudocapacitive electrode materials due to its high specific capacitance, low cost and

environmental compatibility (Deng et al., 2013).

In recent years, concerted efforts have been focused on the preparation and optimization

of manganese dioxide thin films for large-scale commercial production (Yan et al., 2009).

Nanoparticulate manganese dioxide thin films have been comprehensively studied in recent years

in order to gain better knowledge on its intrinsic properties and to determine the relations among

its morphological, structural, and compositional characteristics for enhancing performance as

electrochemical capacitors (Staiti and Lufrano, 2009). Manganese dioxide has been reported to

exhibit specific capacitance as high as 600 F/g for thin films and 150-300 F/g for powder-based

electrodes within a potential window of 0.9-1.2 V in aqueous electrolytes containing KCl, K2SO4,

Na2SO4, or KOH (Yang et al., 2009).

4

Nanostructured manganese dioxide thin films were synthesized mainly by wet chemical

processes such as anodic oxidation, electrodeposition, electroless deposition, successive ionic

layer adsorption and reaction (SILAR), chemical bath deposition, spin coating, dip coating, and

spray pyrolysis, but also by electron beam evaporation, chemical vapor deposition, reactive

sputtering, molecular beam epitaxy, pulsed layer deposition, and atomic layer deposition (Nilsen

et al., 2003). Thin-film deposition methods which involve growth from solution are known as

chemical methods. Chemical deposition methods are inexpensive, enable synthesis of thin-film

materials with complex chemical compositions, and require low operating temperature. The low

deposition temperature is highly desirable in order to avoid effects such as inter-diffusion,

contamination and dopant redistribution. Besides, the morphology of thin films can be easily

controlled via optimizing preparative parameters. Unlike physical deposition methods, chemical

deposition methods do not require high quality target or substrates nor do they require vacuum at

any stage of deposition process (Lokhande et al., 2011).

However, a main drawback in the deposition of MnO2 thin film by chemical methods is

the lack of stable Mn(IV) precursors in aqueous solution (Jacob and Zhitomirsky, 2008).

Chemical vapor deposition has advantages for thin-film manufacture in the industry as it has a

high growth rate, excellent conformality, no requirement for expensive vacuum equipment, and

due to the chemical nature of the process, it tends to produce adherent and durable films

(Warwick and Binions, 2014). However, the chemical vapor deposition (CVD) method is costly

and complicated for mass production (Chaoumead et al., 2013). For metal evaporation or

sputtering, this method can be quite complex requiring raised temperatures and a vacuum system

(Mallick et al., 2006). The hydrothermal method is attractive because of its operational

simplicity, good coating efficiency and capability for large scale production. Furthermore,

5

deposition on a 3D structure is an additional advantage of the hydrothermal deposition method,

with which a thin film can be deposited on all surfaces of supporting substrates (Yan et al.,

2012).

In this study, the novel self-assembly horizontal submersion and the electrophoretic

deposition processes have been demonstrated to be versatile and cost effective deposition

techniques for the deposition and optimization of nanoparticulate MnO2 thin films for the

fabrication of thin-film electrochemical capacitors.