Direct Growth Of Vertically Aligned Carbon Nanotube (VACNT) On Different Conducting Substrates For Electrochemical Capacitor (EC).

(1)

Faculty of Manufacturing Engineering

DIRECT GROWTH OF VERTICALLY ALIGNED

CARBON NANOTUBE (VACNT) ON DIFFERENT

CONDUCTING SUBSTRATES

FOR ELECTROCHEMICAL CAPACITOR (EC)

Raja Noor Amalina Binti Raja Seman

Master of Science in Manufacturing Engineering

(2)

DIRECT GROWTH OF VERTICALLY ALIGNED CARBON NANOTUBE (VACNT) ON DIFFERENT CONDUCTING SUBSTRATES FOR

ELECTROCHEMICAL CAPACITOR (EC)

RAJA NOOR AMALINA BINTI RAJA SEMAN

A thesis submitted

In fulfilment of the requirements for the degree of Master of Science In Manufacturing Engineering

Faculty of Manufacturing Engineering

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

(3)

DECLARATION

I declare that this thesis entitle “Direct Growth of Vertically Aligned Carbon Nanotube (VACNT) on Different Conducting Substrates for Electrochemical Capacitor (EC)” is the result of my own research except as cited in the references. The thesis has not been accepted for any degree and is not concurrently submitted in candidature of any other degree.

Signature : …... Name : ...

(4)

APPROVAL

I hereby declare that I have read this thesis and my opinion this thesis is sufficient in terms of scope and quality for the award of Master of Science in Manufacturing Engineering (Advanced Materials).

Signature : ... Supervisor Name : ... Date : ...

(5)

DEDICATION

(6)

ABSTRACT

Electrochemical capacitor (EC) is highly promising energy device due to its electrical charge storage performance and significant lifecycle ability. Construction of the EC cell especially its electrode fabrication is critical to ensure great application performance. The purpose of this research is to introduce direct growth of vertically aligned carbon nanotube (VACNT) on conducting substrates, namely SUS 310S, Inconel 600, and YEF 50 and their usage as symmetric VACNT electrode in EC. The substrates were deposited by alumina and cobalt catalyst thin films, and then the growth was done by using alcohol catalytic chemical vapour deposition. By this, VACNT was successfully grown and their structures (dimension, walls) have been confirmed by means of electron microscopies. The thickness of the VACNT is typically about 31.68 μm (SUS 310S) and 10.58 μm (Inconel 600), respectively which indicate that no particular agglomerated metals were observed on the exposed surface of the substrate. In contrast, the field emission scanning electron microscopy (FESEM) image obtained shows that most of the entire areas, a thicker carbon products forest/agglomerated was formed on the top surface of YEF 50 substrate. Meanwhile, the transmission electron microscopy (TEM) image reveals that the VACNT on Co/Al2O3/SUS 310S are multi-walled CNTs (MWCNTs)

with the inner and outer diameter of CNTs are approximately 4.89 nm and 16.43 nm, respectively. The Raman spectra results indicate that the CNT was typical of MWCNTs, which is in agreement with the TEM observation. Regardless of the difference in current collectors being used, cyclic voltammetry (CV) analysis from the EC depicted a relatively good specific gravimetric capacitance (Csp) and rate capability performance. A nearly

rectangular-shaped CV curve was observed even at a scan rate of 1000 mV s−1_{. The}

Csp

measured at 1 mV s-1_{was 33.35 F g}-1 _{(SUS 310S), 16.73 F g}-1 _{(Inconel 600), and 24.82 F g}-1

(YEF 50), respectively. Besides, from the charge-discharge measurement, the symmetrical triangular curves reveal that there is no IR drops or voltage drops because of low internal resistance in the electrode for SUS 310S, Inconel 600, and YEF 50 substrates. Also, the VACNT electrode shows excellent discharge behaviour and good capacitance retention of up to 1,000 cycles. Thus, this binder free and aligned CNT structure may provide excellent rate capabilities, high capacitance, and long lifecycle energy device. This is very promising for the development of high energy and high power density of device for multi-scale applications or industries.

(7)

ABSTRAK

Kapasitor elektr okimia mer upa kan alat tenaga yang bagus kerana ia mempunyai pr estasi yang baik dalam penyimpana n cas elektrik da n keupa ya an kitara n hidup yang menarik. Pemasangan sel kapasitor elektrokimia terutama nya dalam fa brika si elektr od sangat kritikal untuk pr estasi aplikasi yang ma ntap. Tujuan penyelidikan ini adalah untuk memperkenalka n pertumbuhan secara langsung karbon na notiub yang menega k sejajar di atas substrat yang boleh mengalir kan arus elektrik dinama ka n sebagai SUS 310S, Inconel 600, dan YEF 50 dan juga kegunaannya sebagai elektrod yang simetri dala m ka pasitor elektrokimia . Semua substrat tela h menjalani proses pemendapa n menggunaka n filem nipis alumina dan kobalt, kemudia n pertumbuhan kar bon nanotiub tela h dila kukan menggunakan alkohol pema ngkin wap kimia pemendapa n. Dengan ini, karbon nanotiub yang menega k sejaja r telah berjaya tumbuh dan str ukturnya (dimensi, dinding) telah disahkan mengguna kan mikroskopi elektron. Ketebalan karbon nanotiub yang menega k sejaja r ialah 31.68 µ m (SUS 310S) dan 10.58 µ m (Inconel 600) menunjukkan tiada kewujuda n pengumpula n loga m di atas per mukaan pada kedua -dua substrat. Sebaliknya, imej FESEM yang diper olehi menunjukkan karbon ya ng tebal terbentuk di atas per mukaan substrat YEF 50 di keba nya kan kawa san,. Sementara itu, imej TEM mendedahkan bahawa

karbon nanotiub yang tumbuh di atas Co/Al2O3/SUS 310S adala h ka r bon nanotiub yang

mempunyai dinding yang banya k dengan diameter luaran dan dala man kar bon nanotiub 4.98 nm dan 16.43 nm. Keputusan ra man spektr um menandakan bahawa karbon nanotiub yang terhasil mempunyai dinding yang banya k, ya ng mana bertepata n denga n pemerhatian menggunakan TEM. Tida k kira perbezaan pengumpulan a rus yang diguna kan, analisis mengguna kan kitar an volta mmetri dari kapasitor elektrokimia menunjukkan spesifik gravimetrik ka pasita n da n ka dar pr estasi keupa yaan yang sangat baik. Hasil pemerhatian mendapati lengkuk menyerupai bentuk segi empat tepat kitaran

volta mmetri yang ter bentuk bertahan sehingga kada r imbasan pada 1000 mV s-1. Nilai

spesifik gr avimetrik ka pasitan diukur pa da kadar 1 mV s-1 ialah 33 35 F g-1 (SUS 310S),

16.73 F g-1 (Inconel 600), dan 24.82 F g-1 (YEF 50). Ta mbaha n juga, daripada

pengukuran kada r alir -pembebasan, lengkuk segi tiga yang simetri menunjukkan tiada penuruna n IR atau penurunan voltan diseba bkan rinta ngan dala man yang r enda h dala m elektrod untuk ketiga -tiga substrat. Elektrod ka rbon na notiub ya ng menega k sejaja r juga mempunyai tingkah la ku pelepasan cas yang a gak cemerla ng dan pengekalan kapasitan yang sangat baik sehingga mencecah 1,000 kitaran. Oleh itu, struktur karbon nanotiub yang menega k a kan menghasilkan ka dar keupayaa n yang sangat cemerlang, ka pasita n yang tinggi, da n kita ran ha yat ya ng panjang bagi alat tena ga . Ini menjanjika n penghasila n ketumpata n tena ga yang tinggi dan kuasa yang tinggi bagi alat untuk diguna kan dala m a plika si skala yang pelbagai dalam industri.

(8)

ACKNOWLEDGEMENT

First and foremost thanks to Allah for helping me to complete this thesis. I would like to express my sincere appreciation to my project supervisor, Dr. Mohd Asyadi Azam Bin Mohd Abid for the encouragement, advices, suggestions and guidance upon completing my research project.

This work was supported by the Ministry of Higher Education Malaysia via Exploratory Research Grant Scheme (ERGS), project entitled “Growth and Characterization of Vertically Aligned Carbon Nanotube on Conducting Substrate using Ethanol-Based Growth Technique”, and I am also thankful for the tuition fees from the MyBrain15 program.

I am grateful to Faculty of Manufacturing Engineering, Universiti Teknikal Malaysia Melaka especially my co-supervisor Dr Noraiham Mohamad, assistant engineers in the laboratory, and my friends for the help and tremendous support for my research. I would like to acknowledge Dr. Ambri from IMEN, Universiti Kebangsaan Malaysia, Bangi for his help in the usage of electron beam physical vapour deposition system to deposit thin films used in this work.

Lastly, I am grateful to my parents, my siblings for the continuous support and encouragement for me to finish up my study. I love you all.

(9)

TABLE OF CONTENTS

PAGE

DECLARATION APPROVAL DEDICATION

ABSTRACT i

ABSTRAK ii

ACKNOWLEDGEMENT iii

TABLE OF CONTENTS iv

LIST OF TABLE vii

LIST OF FIGURES viii

LIST OF ABBREVIATIONS xi

LIST OF SYMBOLS xii

LIST OF PUBLICATIONS xiii

CHAPTER 1. INTRODUCTION 1

1.1 Background 1

1.2 Problem Statement 2

1.3 Objectives 4

1.4 Scopes 5

1.5 Thesis organization 6

2. LITERATURE REVIEW 7

2.1 Carbon nanotubes 7

2.1.1 General background 7

2.1.2 Advantages and properties of vertically aligned CNT 10

2.2 Energy storage device 12

2.2.1 Conventional capacitors 12

2.2.2 Batteries 13

2.2.3 Electrochemical capacitors 14

2.2.4 Comparison of different energy storage devices 16

2.2.5 Main components in ECs 18

2.3 Important factors towards VACNT growth 21

2.3.1 Catalyst and catalyst-support thin films from EBPVD process 21

2.3.1.1 Catalyst thin film 21

2.3.1.2 Catalyst-support thin film 22

2.3.1.3 Electron beam physical vapor deposition 23

2.3.2 CNT growth from CVD process 25

2.3.2.1 Types of CVD process 25

2.3.2.2 Versatility of substrates by using CVD process 26

(10)

2.4 Materials characterization 28

2.5 Electrochemical measurements 33

2.5.1 Cyclic voltammetry analyses 33

2.5.2 Charge-discharge analyses 35

2.6 Summary of chapter 2 37

2.6.1 CNT as electrode material for ECs 37

2.6.2 VACNT growth process 37

2.6.3 Electrochemical measurements 38

3. METHODOLOGY 39

3.1 Flow chart of the experiment 40

3.2 Sample preparation 41

3.2.1 Three different conducting substrates 41

3.2.2 Substrates cutting process 42

3.2.3 Substrates cleaning process 42

3.3 Deposition of catalyst and catalyst-support thin films by using 43

EBPVD technique 3.3.1 Characterization of Al2O3 and Co thin films 45

3.4 Direct growth of VACNT on conducting substrates 45

by using ACCVD technique 3.4.1 ACCVD process 45

3.4.2 Characterization of as-grown VACNT 47

3.4.2.1 Electron microscopies 47

3.4.2.2 Raman spectroscopy 48

3.5 Electrochemical measurements 48

3.5.1 Cyclic voltammetry 48

3.5.2 Charge-discharg 49

3.6 Cell assembly using VACNT electrode 49

4. RESULTS AND DISCUSSION 50

4.1 Surface properties of Co catalyst and Al2O3 catalyst-support 50

thin films 4.1.1 Surface chemical state of Al2O3 and Co thin films 52

by X-ray photoelectron spectroscopy 4.1.2 Summary of analysis on Co catalyst and Al2O3 54

catalyst-support thin films 4.2 Surface morphology of as-grown VACNTs by using FESEM 55

4.2.1 FESEM top view analyses on SUS 310S, Inconel 600, 55

and YEF 50 substrates 4.2.2 EDX analysis of VACNTs on SUS 310S substrate 58

4.2.3 FESEM tilted analyses on SUS 310S, Inconel 600, 59

and YEF 50 substrates 4.2.4 TEM analysis for VACNT growth on Co/Al2O3/SUS 310 64

(11)

4.2.5 Structural analyses of VACNT on SUS 310S, Inconel 600, 66

and YEF 50 substrates by means of Raman spectroscopy 4.2.6 Summary of VACNT growth results 69

4.3 Electrochemical performance of as-grown VACNTs electrode 70

by using 6 M KOH electrolyte 4.3.1 Cyclic voltammetry analyses of VACNT growth 72

on all substrates 4.3.2 Charge-discharge analyses of VACNT electrodes 75

4.3.3 Summary for electrochemical performance analyses 81

5 CONCLUSIONS AND RECOMMENDATIONS 83

5.1 Conclusions 83

5.2 Recommendations 84

(12)

LIST OF TABLES

TABLE TITLE

PAGE

2.1 Comparison between conventional capacitors, batteries, 18 fuel cells, and electrochemical capacitors (Bubna et al., 2012)

3.1 Major information of conducting substrates 41 3.2 EBPVD deposition parameter for catalyst and 44 catalyst-support thin films

3.3 Cyclic voltammetry parameter 48

3.4 Charge-discharge parameter 49

4.1 Data composition from EDX analysis of VACNT 59 on Co/Al2O3/SUS 310S

4.2 Raman spectroscopy analysis; IG/ID ratio, D and G peaks for 68

VACNT on SUS 310S, Inconel 600, and YEF 50 substrates

4.3 Summary of CNT characterization by using FESEM and 69 Raman spectroscopy

4.4 Calculation of average weight or VACNT loading 71 on all substrates

4.5 Csp (in F g-1) for VACNT electrodes on all substrates 75

at various scan rates

4.6 The discharging time with Csp for different applied currents 80

4.7 Summary of Csp calculated from CV and charge-discharge 82 measurement; and capacitance retention results

(13)

LIST OF FIGURES

FIGURE TITLE

PAGE

2.1 The graphene sheet (left) is rolled to form a SWCNT (middle) 8 and MWCNT (right) (Graham et al., 2005)

2.2 Schematic illustration of armchair, zigzag, and 9 chiral structure (Popov, 2004)

2.3 Comparison between aligned CNT and activated carbon 11 based on electron and ion conductivities (Inagaki et al., 2010)

2.4 Schematic diagram of an conventional capacitor 12 (Fernández et al., 2008)

2.5 Schematic diagram of charging-discharging 14 in Li-ion battery (Liu et al., 2010)

2.6 (a) The mechanism of charge-discharge process for EDLC and 16 (b) energy storage mechanism for pseudocapacitor

(Manaf et al., 2013)

2.7 Ragone plot for various energy storage devices 17 (Simon and Gogotsi, 2008)

2.8 Common symmetric electrode cell component for EC 19 (Manaf et al., 2013)

2.9 Common materials coating processes (Singh et al., 2000) 24 2.10 Widely-accepted growth mechanism model for CNTs: (a) tip-growth 27 (b) base growth (Ellis et al., 2012)

2.11 XPS survey scan for Al2O3 sample (Madaan et al., 2013) 29

2.12 XPS narrow spectra of Co 2p and O 1s regions (Petitto et el., 2008) 30

(14)

2.14 TEM image of CNT growth on the Ni foam (Shi et al., 2011) 32 2.15 Raman spectrum of CNT on various substrates 33 (Hiraoka et al., 2006)

2.16 CV profile (Shah et al., 2009) 34

2.17 Charge-discharge curves of graphene oxide in in 1 M H2SO4 36

electrolyte at current applied 2 mA. The samples of GO were electrochemically pre-reduced for 1000 s (black curve), 2000 s (red curve) and 4000 s (blue curve) (Yu et al., 2013)

2.18 EDLCs discharging time taken at current density of 3.8 A g−1 ₃₆

which composed of ACFC and MWCNT sheet electrodes.

The discharge slope was used to calculate the specific capacitance of the device (Honda et al., 2007)

2.19 The specific capacitance of CNT–15%MnO2 electrode as a 37 function of cycle number measured at 20 mV s−1 in

1mol L−1_Na

2SO4 aqueous solution (Yan et al., 2009)

3.1 Flow chart of the experiment 40

3.2 A piece of conducting substrates with 15 mm diameter 42

3.3 Substrates cleaning process flow 42

3.4 Image of EBPVD machine in UKM, and the deposition of 44 catalyst and catalyst-support thin films

3.5 CVD Furnace (MILA-3000) 46

3.6 The heating profile for CNT growth 46

3.7 Schematic diagram of CNT height calculation by using FESEM 47 3.8 Image of VACNT electrodes and the EC components 49 4.1 An example of FESEM image of as-deposited Al2O3 and Co thin films 51

4.2 (a) XPS survey spectrum of Al2O3 on SUS 310S and 53

(b) XPS narrow spectrum of Al2O3 on SUS 310S for Al 2p region

4.3 (a) XPS survey spectrum of Co on SUS 310S and 54 (b) XPS narrow spectrum of Co on SUS 310S for Co 2p region

4.4 Top view FESEM images of samples displaying different 57 CNT yields for SUS 310S (b) Inconel 600 (c) YEF50 substrates

(15)

4.5 FESEM-EDX showing (a) spot (b) elemental composition peaks 58 4.6 Tilted 45˚ FESEM images of samples displaying different 62 CNT yields for (a) SUS 310S (b) Inconel 600 substrates and

4.7 Suggested development of Al2O3 and Co thin films before and during 63

CNT growth process

4.8 TEM image of MWCNT growth on SUS 310S substrate 64 4.9 Typical diameter distribution of MWCNT growth on 65 SUS 310S substrate, determined from TEM; (a) inner diameter

and (b) outer diameter

4.10 Raman spectra of CNT growth collected from 67 different substrates

4.11 IG/ID ratio of different substrates 68

4.12 CV of VACNT electrodes on: (a) SUS 310S 74

(b) Inconel 600 and (c) YEF 50 substrates at different scan rates by using 6 M KOH electrolyte measured from 0.0 to 1.0 V

4.13 Charge-discharge curves measured at constant current of 0.5 mA 77 for three cycles for different substrates which are (a) SUS 310S

(b) Inconel 600, and (c) YEF 50

4.14 Discharging time at different currents for (a) SUS 310S, 79 (b) Inconel 600, and (c) YEF 50 substrates

4.15 Capacitance retention (in %) versus cycle numbers for SUS 310S, 81 Inconel 600, and YEF 50 substrates, of up to 1,000 cycles

(16)

LIST OF ABBREVIATIONS

ACCVD Alcohol Catalytic Chemical Vapour Deposition

CNT Carbon Nanotube

CV Cyclic Voltammetry

CVD Chemical Vapour Deposition

EBPVD Electron Beam Physical Vapour Deposition

EC Electrochemical Capacitor

EDLC Electrochemical Double Layer Capacitor FESEM Field Emission Scanning Electron Microscopy

IL Ionic Liquid

KOH Potassium Hydroxide

MWCNT Multi-Walled Carbon Nanotube

SWCNT Single-Walled Carbon Nanotube

TEM Transmission Electron Microscopy

VACNT Vertically Aligned Carbon Nanotube

(17)

LIST OF SYMBOLS

Al2O3 - Alumina

Co - Cobalt

Csp - Specific gravimetric capacitance

F g-1 _- _{Farad per gram}

g - Gram

k - Kilo

mA - Miliampere

min - Minute

mm - Milimeter

mV s-1 - MiliVolts per second

M - Molar

µm - Micrometer

nm - Nanometer

Pa - Pascal

s - Second

W kg-1 _- _{Watts per kilogram}

Wh kg-1 _- _{Watts hour per kilogram}

(18)

LIST OF PUBLICATIONS

(i) Peer reviewed journals

Seman, R. N. A. R., Azam, M. A. and M. A. Mohamed, Vertically Aligned Carbon Nanotube Directly Grown on Stainless Steel and Inconel Foils for Supercapacitor Electrode. Journal of Nanoscience and Nanotechnolgy. (accepted for publication).

Seman, R. N. A. R., Munawar, R. F., Razak, J. A., Zulkapli, N. N., Bistamam, M. S. A., Talib, E., Kudin, T. I. T., Manaf, N. S. A., and Azam, M. A., 2015. Cyclic Voltammetry Analysis of Carbon Based Electrochemical Capacitor in Aqueous Electrolytes. Applied Mechanics and Materials, 761, pp. 452-456.

Azam, M. A., Dorah, N., Seman, R. N. A. R., Manaf, N. S. A., and Kudin, T. I. T., 2015. Electrochemical performance of activated carbon and graphene based supercapacitor. Materials Technology, 30, pp. A14-A17.

Azam, M. A., Jantan, N. H., Dorah, N., Seman, R. N. A. R., Manaf, N. S. A., Kudin, T. I. T., and Yahya, M. Z. A., 2015. Activated carbon and single-walled carbon nanotube based electrochemical capacitor in 1 M LiPF6 electrolyte. Materials Research Bulletin, 69, pp. 20-23.

Talib, E., Lau, K. T., Zaimi, M., Bistamam, M. S. A., Manaf N. S. A., Seman, R. N. A. R., Zulkapli, N. N., and Azam, M. A., 2015. Electrochemical Performance of Multi Walled Carbon Nanotube and Graphene Composite Films Using Electrophoretic Deposition Technique. Applied Mechanics and Materials, 761, pp. 468-472.

(19)

Zulkapli, N. N., Manaf, M. E. A., Maulod, H. E. A., Manaf, N. S. A., Seman, R. N. A. R., Bistamam, M. S. A., Talib, E., and Azam, M. A., 2015. Control of Cobalt Catalyst Thin Film Thickness by Varying Spin Speed in Spin Coating towards Carbon Nanotube Growth. Applied Mechanics and Materials, 761, pp. 421-425.

Azam, M. A., Hassan, A., Mohamad, N., Talib, E., Manaf, N. S. A., Zulkapli, N. N., Seman, R. N. A. R., and Bistamam, M. S. A., 2015. Fabrication of Activated Carbon Filled Epoxidized Natural Rubber Composite Using Solvent Casting Method. Applied Mechanics and Materials, 761, pp. 426-430.

(ii) Conference presentation

Vertically Aligned Carbon Nanotube Directly Grown on Different Metal Alloy Substrates for Supercapacitor Electrode, Energy Materials Nanotechnology, Holiday Inn Resort Phuket Thailand, 4-7 May 2015 (Oral)

Cyclic Voltammetry Analysis of Carbon Based Electrochemical Capacitor in Aqueous Electrolytes, 3rd International Conference on Design & Concurrent Engineering 2014 -iDECON2014, Avilion Legacy Hotel Melaka Malaysia, 22-23 September 2014 (Oral)

Activated Carbon and Single-Walled Carbon Nanotube Based Electrochemical Capacitor in 1 M LiPF6 Electrolyte, International Symposium on Functional Materials-ISFM 2014, Novotel Hotel Singapore, 4-7 August 2014 (Oral)

Electrochemical Performance of Activated Carbon and Graphene based Supercapacitor, International Symposium on Advanced Functional Materials-ISAFM 2014, Monash University Kuala Lumpur Malaysia, 1-2 August 2014 (Oral)

(20)

CHAPTER 1

INTRODUCTION

1.1 Background

Since the discovery of electricity, there has been the sought of effective methods to store the energy for the used in demand. Energy storage devices offer a powerful technological approach to manage power supply in order to produce more resilient energy framework and bring cost effective to societies. Also, the existing of advanced technology in modern economy and society demands the execution and design of cheap, good efficiency, and various infrastructures for energy storage systems (Pint et al., 2011).

There is some of the different technologies are predicted to provide the country with renewable energy in the long term period such as hydroelectric systems, biomass, wind power, solar thermal and geothermal systems. In particular, fuel cells, batteries, electrochemical capacitors (ECs), and conventional capacitors are being used as energy storage devices due to their excellent in enhancing the energy or power densities and becoming more critical to supply energy within a relatively short or long period of time. However, by increasing the energy and power densities of the devices is highly desirable seems their performance are measured by these characteristic (Kim et al., 2012).

Among the energy storage devices, ECs have appeared as the most promising for the upcoming energy challenge (Simon and Gogotsi, 2008; Yang et al., 2011). Moreover, some potentially electrode materials with high specific area like single-walled carbon nanotubes (SWCNTs) are being used in EC application especially in electrochemical

(21)

double-layer capacitors (EDLCs) (Sharma and Bhatti, 2010). The present of available electrodes in the energy storage devices such as low electrolyte accessibility with narrow electrochemical window, flammability, toxicity, thermal instability and low capacitance have restricted the performance of the devices. With these limited properties, there is a need to overcome this problem in order to develop high performance EC with high rate performance, and long lifecycle (Lu et al., 2009).

Carbon nanotube is being used as electrode materials in EC application because they possess high conductivity, continuous conductive paths, low mass density, regular pore structures, high mechanical strength and high chemical stability (Zhang et al., 2009; Merkoci et al., 2005; Kim et al., 2005; Kim et al. 2002). Moreover, it is possible to synthesize the CNTs directly on current collector substrates without using binder agents. There has been extensively study about the growth of vertically aligned carbon nanotubes (VACNTs) due to it produce high yield and uniformity as well as homogeneous distribution of nanotube growth (Vinten et al., 2011).

1.2 Problem Statement

Recent work on aligned CNT has drawn increasing attention since aligned CNT have shown good characteristic in various applications (Bistamam and Azam, 2014) such as nanoscale electronic devices (Murakami et al., 2000), ECs (Chen et al., 2004), and sensors (Arab et al., 2006). Previously, quartz and silicon wafer have been used as non-conducting substrates to synthesis VACNT. In spite of that, these non-conducting substrates have been replaced with conducting substrates to be used in EC application to directly grow VACNT. This is because it provides excellent electrical contact among the substrate and VACNT and thus will increase the conductivity of electrode materials.

(22)

Therefore, the process to assemble the electrode materials make easier because there is no need to have additional materials to prepare the electrode materials including conductive additive and binders (Zhang et al., 2007). There are various method to grow VACNTs on conducting substrates including liquid dip-coating method (Parthangal et al., 2007), bias-enhanced microwave plasma chemical vapour deposition (CVD) (Lin et al., 2004), and vapour-phase catalyst delivery method (Katayama et al., 2001).

In contrast, physical transfer techniques such as flip-over (Kim et al., 2006), lift-off (Chai et al., 2007), and contact transfer techniques (Kumar et al., 2006) have been introduced to transfer VACNT on conducting substrates. Although this technique was reliable, it will result in poor electrical contact between substrate and CNT electrode and known as complicated processes which can affect electrochemical properties of the VACNT. In addition, conventional coating was used in preparing the slurry to fabricate the electrode material for EC. This method needed a binder material as insulating material which directly can affect the electrochemical performance of electrode. Meanwhile transfer technique was introduced to minimize the internal resistance of the electrode. CNT was grow on Silicon wafer substrate by CVD process, then CNT with catalyst thin films were cutting by using razor blade and pasted on conducting substrate for EC application. This method will increase the number process steps.

In order to enhance the electrode performance in various applications especially in ECs, aligned CNT that shows excellent performance are required because its possess good properties including high mechanical strength and good electrical conductivity. Many efforts have been made by researchers to optimize and improve the properties of aligned CNT structure. The direct growth of CNT on conducting substrate is highly desirable in EC application to minimize the contact resistance between substrate and CNT. This

(23)

technique was develop particularly by using low cost ethanol vapour gas and metal catalyst thin film in order to optimize the high precision of CNT growth for electronic device application. By developing the direct growth technique, binder free and additional process step in device fabrication can be avoided which might introduce internal resistance at once affecting charge storage performance of EC (Lu and Dai, 2010).

From the above justification and explanation, the direct growth technique was choosing in this research. By using direct growth technique it will produce superb electrical contact between substrate and CNT compared to physical transfer technique which can increase the conductivity of electrode materials. Also, this is simple technique because there is no need the binder and conductive additives material which will influence the performance of device fabrication.

1.3 Objectives

The objectives of this research are as follows:

1) To synthesis vertically aligned carbon nanotube (VACNT) on conducting substrates by using ethanol based growth technique.

2) To characterize as-grown VACNTs by using morphological and analytical techniques.

3) To assess electrochemical performance of VACNT electrode by using cyclic voltammetry and charge-discharge.

(24)

1.4 Scopes

The scope of this research is to grow the VACNT on various conducting substrates by using ethanol based growth technique. The substrates or foils are SUS 310S, Inconel 600, and YEF 50, and the main focus is to determine the VACNT growth performance as well as the electrochemical performance VACNT electrode in EC. In order to directly grow VACNT, there is a need to prepare the catalyst and catalyst-support thin films. The electron beam physical vapour deposition (EBPVD) system was used to prepare the thin films. In specific, cobalt (2-6 nm) and alumina (20-30 nm) were used as catalyst and catalyst-support, respectively. The CVD temperature and processing time for CNT growth were fixed to 700 °C and 10 min, respectively.

The as-grown VACNTs on the substrates were characterized by using electron microscopies; FESEM, TEM, and Raman spectroscopy. For the confirmation of VACNT morphology and dimension (thickness), FESEM and TEM were used. The structural information of VACNT was characterized by using Raman spectroscopy. Further, VACNT electrodes were prepared to evaluate the electrochemical performances by using cyclic voltammetry (CV), and charge-discharge. Various scan rates including 1, 5, 10, 50, 100, 250, 500, and 1000 mV s-1 _{were used to evaluate the charge storage ability of all electrode}

materials. Meanwhile, charge-discharge was tested up to 1,000 cycles to investigate the charge-discharge characteristic from the electrode materials. For the fabrication of EC, aqueous electrolyte, 6 molar potassium hydroxide (6 M KOH) was used as the electrolyte, and polypropylene (PP) as the separator.

(1)

xiv

(ii) Conference presentation

(2)

1 CHAPTER 1

INTRODUCTION

1.1 Background

(3)

1.2 Problem Statement

(4)

In contrast, physical transfer techniques such as flip-over (Kim et al., 2006), lift-off (Chai et al., 2007), and contact transfer techniques (Kumar et al., 2006) have been introduced to transfer VACNT on conducting substrates. Although this technique was reliable, it will result in poor electrical contact between substrate and CNT electrode and known as complicated processes which can affect electrochemical properties of the VACNT.In addition, conventional coating was used in preparing the slurry to fabricate the electrode material for EC. This method needed a binder material as insulating material which directly can affect the electrochemical performance of electrode. Meanwhile transfer technique was introduced to minimize the internal resistance of the electrode. CNT was grow on Silicon wafer substrate by CVD process, then CNT with catalyst thin films were cutting by using razor blade and pasted on conducting substrate for EC application. This method will increase the number process steps.

(5)

1.3 Objectives

The objectives of this research are as follows:

1) To synthesis vertically aligned carbon nanotube (VACNT) on conducting substrates by using ethanol based growth technique.

2) To characterize as-grown VACNTs by using morphological and analytical techniques.

3) To assess electrochemical performance of VACNT electrode by using cyclic voltammetry and charge-discharge.

(6)

1.4 Scopes

Direct Growth Of Vertically Aligned Carbon Nanotube (VACNT) On Different Conducting Substrates For Electrochemical Capacitor (EC).

Faculty of Manufacturing Engineering