UNIVERSITI TEKNIKAL MALAYSIA MELAKA

GRAPHENE AND CARBON NANOTUBE BASED

ELECTROCHEMICAL CAPACITOR IN AQUEOUS

ELECTROLYTE

This report submitted in accordance with requirement of the Universiti Teknikal

Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering

(Engineering Materials) (Hons.)

by

NURUL HAZIMAH BINTI JANTAN

B051110077

891105-04-5240

FACULTY OF MANUFACTURING ENGINEERING

2014

DECLARATION

I hereby, declared this report entitled “Graphene and Carbon Nanotube Based

Electrochemical Capacitor in Aqueous Electrolyte” is the result of my own research

except as cited in references.

Signature : ……………………………………….

Author‟s Name : NURUL HAZIMAH BTE JANTAN

Date :

APPROVAL

This report is submitted to the Faculty of Manufacturing Engineering of UTeM as a

partial fulfillment of the requirements for the degree of Bachelor of Manufacturing

Engineering (Engineering Materials) (Hons.). The members of the supervisory

committee are as follow :

………………………………

(DR MOHD ASYADI AZAM BIN MOHD ABID)

i

ABSTRAK

Kapasitor elektrokimia (EC) adalah alat penyimpanan elektrokimia yang mempunyai

kepadatan tenaga dan ketumpatan kuasa yang melengkapi peranan sebagai bateri

(tenaga yang tinggi) dan kapasitor konvensional (kuasa yang tinggi) untuk

menyimpan tenaga dan mengalirkan kuasa. Menariknya terdapat daya tarikan yang

besar daripada penyelidik mengenai penggunaan bahan-bahan berasaskan karbon

bagi menghasilkan elektrod untuk EC . Ini adalah kerana, karbon mempunyai banyak

kebaikan antaranya ialah ianya mudah dihasilkan, mesra alam, konduksi elektrik

yang bagus, luas permukaan yang tinggi dan kos yang agak rendah. Dalam kajian

ini, EC telah dihasilkan dengan menggunakan graphene dan nanotiub karbon

menjajar pelbagai dinding (MWCNTs) sebagai bahan elektrod dan juga campuran

bahan pengikat dengan nisbah 47.5:47.5:5. 6M KOH dan 1M H2SO4 juga telah

digunakan sebagai elektrolit. Ukuran voltammetri berkitar (CV) telah dijalankan

untuk menentukan nilai kapasiti, kitaran hayat dan penentuan jenis EC. Prestasi

cemerlang oleh EC, boleh dikaitkan dengan struktur fizikal dan kekonduksian

intrinsik yang terdapat pada graphene dan MWCNT sebagai bahan elektrod. Nilai

kapasitan tertentu yang diperolehi daripada eksperimen adalah 12.07 F/g (6M KOH

elekrolit) dan 4.34 F/g (1M H2SO4).

ii

ABSTRACT

Electrochemical capacitors (ECs) are electrochemical storage devices which possess

the energy densities and power densities which complement the role of batteries

(high energy) and conventional capacitors (high power) for storing energy and

delivering power. Interestingly there are of great interest from researchers about

using carbon materials based electrode for ECs due to their accessibility, an easy

processability, environmental friendly, good electrical conductivity, high surface

area, and relatively low cost. In this study, ECs were fabricated by using graphene

and multiwalled carbon nanotubes (MWCNTs) as EC electrode material as well as

binder with ratio 47.5:47.5:5. Also, 6M KOH and 1M H2SO4 were used as

electrolyte. Electrochemical measurements such as cyclic voltammetry (CV) were

performed to determine the capacitance value, lifecycle and determination of

fabricated EC. The excellent performance can be attributed to the physical structures

and the intrinsic conductivity owing by the EDLC graphene and MWCNT electrode.

The specific capacitance value gained from the experiment was 12.07 F/g (6M KOH

electrolyte) and 4.34 F/g (1M H2SO4).

iii

DEDICATION

I dedicated this entire work to my beloved family especially to my husband, my

father and mother and also to my fellow friends, supervisor and lecturers for their

support and encouragement throughout this project

iv

ACKNOWLEDGEMENT

First and foremost, I would like to thank God for giving me the strength to carry out

this course of research. Then, I would like to express my sincere thanks and

appreciation to the following people and organization who have directly or indirectly

given generous contributions towards the success of this academic study.

First in the list, I would like to express my sincere appreciation to my respectful

supervisor, Dr. Mohd Asyadi „Azam b. Mohd Abid for his guidance, advice and

encouragement throughout this project. I would like also to take this opportunity to

thank my beloved parents and family members for their support, cares and kindness

throughout the period study.

Last but not least, I would like to acknowledge my colleagues for their support and

commitment in helping me throughout the completion of this report. Without those

helps, this research report would not have been completed successfully.

v

TABLE OF CONTENT

Abstrak i

Abstract ii

Dedication iii

Acknowledgement iv

Table of Content v

List of Tables viii

List of Figures ix

List Abbreviations, Symbols and Nomenclatures xi

CHAPTER 1 : INTRODUCTION 1

1.1 Background 1

1.2 Problem Statement 4

1.3 Objectives 5

1.4 Scope of Research 6

CHAPTER 2 : LITERATURE REVIEW 7

2.1 Electrochemical Capacitor 7

2.1.1 Electrochemical Double Layer Capacitor (EDLC) 8

2.1.2 Pseudocapacitor 9

2.2 Electrode Material 10

2.2.1 Carbon as Electrode Material 10

2.2.1.1 Graphene 11

2.2.1.2 Carbon Nanotube (CNT) 13

2.2.1.3 Other Carbon Materials 16

2.3 Electrolyte 17

2.3.1 Aqueous Electrolyte 18

2.3.2 Non Aqueous Electrolyte 19

2.4 Characterization Techniques 20

2.4.1 Electrode Characterization 21

2.4.1.1 Scanning Electron Microscope (SEM) 21

vi

2.4.2 Electrochemical Measurements 22

2.4.2.1 Cyclic Voltammetry (CV) 22

2.4.2.1.1 CV of Non-Faradaic Process 24

2.4.2.1.2 CV of Faradaic Process 24

CHAPTER 3 : METHODOLOGY 26

3.1 Electrochemical Capacitor Construction 28

3.2 Electrode Material Preparation 29

3.3 Fabrication Process to Produce the EC 35

3.4 Electrode Characteristic 35

3.5 Experimental Set up for CV Analysis 36

3.6 Set up for Prototype Development 37

CHAPTER 4 : RESULT AND DISCUSSION 40

4.1 Result of EC fabrication 40

4.2 Surface Morphology Analysis by SEM 42

4.2.1 EDX Analysis 44

4.3 Cyclic Voltammetry Analysis of The Fabricated EC 45

4.3.1 Specific Capacitance Value 45

4.3.2 Type of Fabricated EC 47

4.3.3 The performance of The EC by Varying The Value 48

of Scan Rate

4.3.4 Csp for Multiple Cycles 51

4.3.4.1 Graphene and MWCNT 52

4.3.4.1.1 6M KOH Electrolyte 52

4.3.4.1.2 1M H2SO4 Electrolyte 54

4.3.4.2 Activated Carbon and SWCNT 56

4.3.4.2.1 6M KOH Electrolyte 57

4.3.5 Problem during CV Testing 59

4.4 Prototype Development 60

4.4.1 Fabrication of EC in the Coin Cell 60

4.4.2 EC Coin Cell Testing 62

vii

CHAPTER 5 : CONCLUSION AND RECOMMENDATION 64

5.1 Conclusion 64

5.2 Recommendation for Future Work 65

REFERENCES 66

APPENDIX A

Academic Achievement

APPENDIX B

Gantt Chart

viii

LIST OF TABLES

Table Title Page

1.1 Comparison of Batteries, ECs and Conventional Capacitors 2

2.1 Properties of Graphene 11

2.2 The Summary of Graphene 12

2.3 The Summary of CNT 14

2.4 Properties of Various Materials used in EC electrode materials 16

(Simon, 2008)

2.5 The Type of The Electrolytes and it Charge of the Ions 17

2.6 Comparison between Aqueous and Non Aqueous 19

2.7 Properties of Various Electrolyte (Simon, 2008) 20

3.1 Materials and its Function 29

3.2 Apparatus and Its Function 31

3.3 Materials used and its Weight 34

3.4 The Component to Produce Circuit 38

4.1 The Composition of Materials used in the Electrode Fabrication 40

4.2 The Composition of Materials used in the Electrode Fabrication 41

4.3 Mass of Different Electrode Materials 42

4.4 The Csp Result with Different Scan Rate 49

4.5 The Value of Csp for Different cycle 51

ix

LIST OF FIGURES

Figure Title Page

1.1 Plot of Power Density (Wkg-1

) versus Energy Density (Whkg-1

) of 2

Different Storage Devices (Rolison et al, 2009)

2.1 The Schematic EDLC (Retrieved from http://www.murata .com/) 8

2.2 The Operating Principle in Electrical Double-layer Capacitors 9

(Retrieved from http://www.murata .com/)

2.3 Schematic of Pseudocapacitor (Josie,2011) 9

2.4 A CV Potential Waveform with Switching Potentials 23

(Wang et al. 2000)

2.5 The Expected Response of Reversible Redox Couple during a Single 23

Potential Cycle (Wang et al. 2000)

2.6 A Schematic Cyclic Voltammogram of a Reversible Redox Process 25

(Si et al, 2008)

3.1 Flow Chart of Methodology 27

3.2 Example of EC Construction 28

3.3 Slurry Preparation 34

3.4 SEM Model EVO50 ZEISS 36

3.5 WonATech (WBCS3000) Voltammetry System 36

3.6 The Circuit for Testing EC 37

3.7 The Circuit for Testing EC 39

4.1 The Electrode with Carbon Material on Stainless Steel Mesh 41

4.2 Surface Morphology of Graphene and MWCNT as Electrode Material 43

4.3 Surface Morphology of Activated Carbon and SWCNT as Electrode 43

Material

4.4 EDX Analysis of Electrode Before use 44

4.5 EDX Analysis of Electrode after Immersed in 6M KOH Electrolyte 45

x

for 4 Hours

4.6 CV Curve with different Scan Rate 46

4.7 The Curve of EC in CV Analysis 48

4.8 The Shape of CV Curve with Different Scan Rate (Hsia et. al, 2014) 49

4.9 The Graph Csp versus Scan Rate 50

4.10 The CV Curve for 5 Cycles with Scan Rate 54

4.11 The CV Curve for 5 Cycles with Scan Rate 56

4.12 The CV Curve for 5 Cycles with Scan Rate 58

4.13 The Failed Shape in CV Curve 59

4.14 The Jig use in CV Testing 59

4.15 The Material and Equipment to Fabricate the EC 60

4.16 The Arrangement of EC in the Coin Cell Battery 61

4.17 The Crimping Process in the Glove Box 61

4.18 The Completed EC in the Coin Cell Battery 61

4.19 LED Circuit Model to Testing the EC 62

4.20 Common Adapter Charger 62

4.21 3V EC with 6M KOH Electrolyte 63

4.22 The Successfully of EC Testing 63

xi

LIST OF ABBREVIATIONS, SYMBOLS, AND

NOMENCLATURE

AC - Activated Carbon

°C - Degree Celsius

CNT - Carbon Nanotube

Csp - Cpecific Cpacitance

CV - Cyclic Voltammetry

EC - Elecrochemical Capacitor

EDLC - Electrochemical Double Layer Capacitor

EDX - Energy Dispersive X-ray

FGS - Functionalized Graphene Sheets

H2SO4 - Sulfuric Acid

KOH - Potasium Hydroxide

LiPF4 - Lithium

MWCNT - Multiwall Carbon Nanotube

SEM - Scanning Electron Microscopy

SSA - Specific Surface Area

SWCNT - Singlewall Carbon Nanotube

1

CHAPTER 1

INTRODUCTION

1.1 Background

Nowadays, the need of energy has become increasing because both of households

and industries require large amounts of power. Due to a lot of problems in

environmental pollution, there is a need for green and clean renewable energy to

assure the sustainable growth of communities As a result, the electrochemical

capacitors (ECs) have become as an alternative to conventional electric energy

storage device.

ECs, also known as supercapacitors or ultracapacitors are energy storage devices that

combine the high energy storage capability of batteries with the high power delivery

capability of capacitors (Burke, 2000). Basically, ECs can be classified into three

types which are electrochemical double layer capacitors (EDLCs), pseudocapacitors,

and hybrid capacitors. Among them, the EDLCs are the most common type for ECs

because of the least cost to manufacture.

In addition, it have to tend great attention not only for the established applications as

backup power for mobile devices and electronic equipments, but also for high power

applications in pulsed lasers and electric vehicles.

2

Figure 1.1 : Plot of power density (Wkg-1

) versus energy density (Whkg-1

) of different storage devices

(Rolison et al., 2009)

From Figure 1.1, the ECs resides in between batteries and conventional capacitors,

these clearly shows that the ECs have both high energy density and power density

than any other storage device.

Table 1.1 : Comparison of Batteries, ECs and Capacitors (Rolison et al., 2009)

Available

Performance Batteries

Electrochemical

Capacitors (ECs)

Conventional

Capacitors

Charge Time 1 to 5 hrs 0.3 to 30 s 10-3

to 10-6

s

Discharge Time 0.3 to 3 hrs 0.3 to 30 s 10-3

to 10-6

s

Energy (Whkg-1

) 20 to 100 1 to 10 < 0.1

Lifecycle 1000 >500,000 >500,000

Power Density (Wkg-1

) 50 ~ 200 1,000 ~ 2,000 >10,000

Charge / discharge

efficiency 0.7 to 0.85 0.85 to 0.98 >0.95

Operating Temperature -20 to 100 °C -40 to 65 °C -20 to 65 °C

3

Table 1.1 shows the comparison between the batteries, ECs can store large amount of

amount of energy and power compared to conventional capacitors and battery

compared to conventional capacitors. Furthermore, it also can be recharged in

seconds rather than hours, it can withstand with cold temperature, shocks, and

vibrations and it can be charged and discharged hundreds of thousands of times

before they wear out. The EC is much easier on the environment than batteries,

because the ECs contain earth abundant and nontoxic materials.

Although all the above devices have different mechanism, but there are also

electrochemical similarities of these three systems. The common features are the

energy providing processes that take place at the phase boundary of the electrode

interface and the separation of electron and ion during the transportation processes.

In this study, graphene and carbon nanotube (CNT) were used as electrode materials

because graphene has been known as one of the most promising active material for

ECs which posses outstanding electrical conductivity and large surface area. Since

the CNT is known as a porous material, it becomes a potential candidates to fabricate

EC. All of the carbon atoms are surface atoms is consequently and extremely large

surface areas may be obtainable if the CNTs can be assembled in a manner that

maximizes the surface area by minimizing CNT bundling and optimizing the

porosity of the CNT electrode.

4

1.2 Problem Statement

The production of energy by using the conventional method will leads to the global

warming problems such as environmental pollution, petroleum exhaustion, climate

change and the greenhouse effect. In response to reduce the output of carbon dioxide,

the several countries have been decided to shut down the old nuclear power plants

and not to build it with new ones. Apart from that, the energy demand has risen and

the price of conventional energy sources has increased dramatically. This situation

makes the reliance of national economies on a continuous and undistorted supply of

such sources has become critical.

Thus, the old energy production method need to be replaced with new ones which

include the concepts that enriching the life style, diminishing wasteful energy and

environment friendly. These new method including solar power, wind power, and

hydroelectricity in its many forms, but these new methods have the disadvantages

compared to the older methods. The output of the older methods is easy to adjust

based on the power requirements. The new energy production method is more

directly by using the power of the nature and as their peak power outputs may not

match with the power requirement. These may result to large volatilities the power

output in monthly or even annual cycles and also the demand can vary monthly or

annually.

Therefore, the energy storage is a very important factor to make these new sources to

become completely reliable as the main sources of energy. Essentially, when the

production level is less than the required need, the energy from these sources must be

stored when extra is produced and then released. These energy storage technologies

show the largeness of an important part of efficient and effective renewable and

distributed generation unit. It is important to develop low cost, high performance and

environmental friendly energy conversion and storage systems in order to make the

effective use of renewable energy. Fuel cells, batteries, ECs and conventional

capacitors are the system required for promising electrochemical energy conversion

and storage. Nowadays, researchers focus on the EC to improve their energy density

since its power density and lifecycle had been already higher than batteries.

5

In order to increase energy storage, EC must use the porous materials as electrode in

order to store ions in the pores at an atomic level. Usually the activated carbon is

used to fabricate the EC‟s electrodes. The fact that activated carbon is not suitable as

electrode material due to the charge carriers are larger size to the pores in the

material and some of them cannot fit into smaller pores. As a result, it will reduce the

storage capacity in the EC performance.

There are many factors that need to take as consideration in order to improve the

energy density of the ECs such as type of electrode and electrolyte material. In this

report, carbon material (graphene and carbon nanotube) will be used as electrode

material because of its contributed to a high value capacitance. This is due to their

special characteristic which is a porous material. The cyclic voltammetry (CV) will

be used to measure the value of capacitance and to determine whether the fabricated

EC is EDLC or pseudocapacitor, and lifecycle. If EC can increase its energy density

in the future, then the use of the battery can be replaced.

1.3 Objectives

In this study, there are two parameters were made constant throughout the

experiment which are the substrate (stainless steel mesh) and electrode material

(graphene and CNT). The main objectives of this research are :

(i) To fabricate the EC by using graphene and CNT as the electrode

material.

(ii) To analyze the fabricated electrochemical capacitor by using cyclic

voltammetry.

6

1.4 Scope of Research

In this study, the major scope will be focused on the fabrication of EC and analyze

the fabricated EC by using CV. The experiment was conducted at the Ionic Materials

& Devices Research Laboratory (iMade) Faculty of Applied Science, University

Teknologi Mara (UiTM) Shah alam and Material Laboratory Faculty of

Manufacturing, Universiti Teknikal Malaysia Melaka (UTeM). Fabrication and

analyze of EC was carried out in UiTM Shah Alam before it is testing by using

model development in the Material Laboratory in UTeM. In this experiment, carbon

materials use as an electrode are graphene and CNT. 1M H2SO4 and 6M KOH was

used as an electrolyte material. Then, the electrode are characterized by using SEM

to obtain the morphology of electrode material. The CV was used to measure to

obtain the capacitance value, lifecycle, and determination of the fabricated EC. The

result obtained was compared to the previous research to see the difference.

7

CHAPTER 2

LITERATURE REVIEW

2.1 Electrochemical Capacitors (ECs)

Basically ECs can be categorized into two parts which are electrochemical double

layer capacitors (EDLCs) and pseudocapacitors. The difference between these

capacitors are their storage principle, which is for EDLC, the electrostatic storage of

the electrical energy can be achieved by separation of charge in a Helmholtz double

layer at the interface between the electrode and electrolyte surface. The distance of

the static separation of charge in a double-layer is of the order of a few Å (0.3–

0.8 nm) which is extremely small. Meanwhile for pseudocapacitor, the

electrochemical storage of the electrical energy with electron transfer was achieved

by a redox reaction with specifically adsorbed ions from the electrolyte, The

intercalation of atoms in the layer lattice or electrosorption, under potential

deposition of hydrogen or metal adatoms in surface lattice sites which result in a

reversible faradaic charge-transfer (Namisny, 2013).

8

2.1.1 Electrochemical Double Layer Capacitor (EDLC)

Figure 2.1 : The Schematic EDLC (Retrieved from http://www.murata.com)

Figure 2.1 shows how an EDLC is made up from a separator, electrolyte, activated

carbon and current collector. Usually the activated carbon is used as the electrode,

because it gives the extremely high specific surface area, relatively low cost, ultra

high capacitances are possible within a small package size. EDLC can achieve high

life cycle seems it has no chemical reaction

The operating principle of EDLC is based on the electrical double layer that can be

formed between the electrode and electrolyte interface. Figure 2.2 shows the basic

principle behind the capacitor. Electrolytic fluid is used in its solid form, and the

electrode is solid form. When the electrode and electrolyte material come in contact

with each other, the positive and negative poles are distributed relative to each other

over and extremely short distance. This phenomena was known as an electrical

double layer. When an external electric field is applied, the electrical double-layer

that is formed in the vicinity of the electrode‟s surface within the electrolytic fluid is

used as the fundamental capacitor structure. (Elna, 2011)

9

Figure 2.2 : The Operating Principle in Electrical Double-layer Capacitors (Retrieved from

http://www.murata.com)

2.1.2 Pseudocapacitor

The pseudocapacitor is the combination of battery and capacitor. For EDLC the

storage principle is electrostatically, whereas pseudocapacitors also store energy

through a chemical reaction whereby a faradic charge transfer occurs between the

electrolyte and the electrode. Pseudocapacitor is asymmetric in that sense that one of

the two electrode layers is a carbon based capacitor electrode while the second

electrode is similar with secondary batteries that use a transition metal oxide. The

storage mechanisms are both reversible and can be charged and discharged 10000 of

time. The Figure 2.3 shows how the pseudocapacitor is made up from faradaic

reaction similar to the battery at the positive electrode. While in negative electrode,

they use the double layer phenomena by using activated carbon with high surface

area to give the great performance of pseudocapacitor. (Josie, 2011)

Figure 2.3 : Schematic of Pseudocapacitor (Josie, 2011)

10

2.2 Electrode Material

The electrode material is a very important part for the ECs to determine the

properties of ECs. Nowadays more work has been done by using microporous

carbons compared with the other materials and most of the commercially available

devices commonly use are carbon electrodes. Below, will discuss about why the

carbon materials always be used as an electrode. In this experiment, the electrode

material that will use is graphene and CNT.

2.2.1 Carbon as Electrode Material

Carbon due to different allotropes (diamond, graphite, fullerenes/nanotube), various

microtextures (more or less ordered) owning to the degree of graphitization, a rich

variety of dimensionality from 0 to 3D and ability for existence under different forms

(from powders to fibres, foams, fabrics and composite) represents a very attractive

material for electrochemical application, especially for the storage of energy

(Frackowiak et al., 2001).

EC can deliver and store energy at relatively high rates because the mechanism of

energy storage is simple charge operation. The EC vasts increase in capacitance in

achieved due to the combination of an extremely small distance that separates the

opposite charges, as defined by the electric double layer; and highly porous

electrodes that embody very high surface areas.

Carbon has becoming more atterctive as an electrode material due to its combination

of chemical and physical properties such as high conductivity, good corrosion

resistance, high surface–area (~1 to >2000 m2/g

2), high temperature stability,

controlled pore structure, and good processabillity and compatibility

A variety of porous forms of carbon are currently preferred as the electrode materials

because they have relatively high electronic conductivity and exceptionally high

surface areas. The physical and chemical characteristic of the carbon electrodes