The effects of carbon nanotube on the properties of graphite-carbon black-polypropylene composite for bipolar plate.

SUPERVISOR DECLARATION

"I declare that I have read this thesis and in my opinion this report is sufficient in terms of scope and quality for the award of the degree of Bachelor of Mechanical Engineering

(Structure & Materials)"

Signature

Supervisor

Date

Ｂｾ＠

...

: DR. MOHD ZULKEFLI BIN SELAMAT

:30MAY2013

DR. MOHD ZULKEFU BIN SELAMAT Pensyarah Kanan

THE EFFECT OF CARBON NANOTUBE ON THE PROPERTIES OF GRAPIDTE-CARBON BLACK-POLYPROPYLENE COMPOSITE FOR

BIPOLAR PLATE

ANINORBANIY AH BINTI BAIRAN

This report is submitted to Faculty of Mechanical Engineering as a requirements to get award of

Degree of Mechanical Engineering ( Structure & Material)

Faculty of Mechanical Engineering UniversitiTeknikal Malaysia Melaka

DECLARATION

" I hereby declare that the work in this report is my own except for summarise and

quotations which have been duly acknowledgment."

Signature:

Author:

Date:

ﾷﾷﾷﾷﾷＭｾﾷＭﾷﾷﾷﾷﾷﾷﾷ

ﾷﾷﾷﾷﾷﾷﾷﾷﾷﾷﾷﾷﾷﾷﾷﾷﾷ

ﾷﾷﾷ＠

ANJNORBANIY AH BINTI BAIRAN

30MAY2013

iii

ACKNOWLEDGEMENT

Ahamdulillah, in the name of Allah and His blessness, I would like to record my appreciation to my supervisor, Dr. Mohd Zulkefli Bin Selamat for their kindness to give me a great opportunity for doing my Final Year Project (FYP). They have been providing me with advice and guidance from the very early stage of this research as well as giving me an extraordinary experience throughout the work. Also his Research Assistant, Mr. Mohd Shakir Bin Ahmad for his help and valuable guiding during my work.

It is an honor for me to acknowledge a panel, Dr Mohd Yusoff Bin Sulaiman, Dr.

Mohd Juzaila Bin Abd. Latif and En. Hamzah Bin Mohd Dom which evaluated my work and give good advice during the presentation of the FYP.

In addition, I would like to thanks to Fakulti Kejuruteraan Mekanikal for final year project team especially En Nidzamuddin Bin Yusuf and all his staff. They have given a lot of information and facilities throughout the run of the FYP.

I am also grateful to my friends who have also been great to work with. I am happy to thank Fairuz, Yusri, Aisamudin and Natasya for their willingness to share their bright thoughts with me.

iv

ABSTRACT

In this study, the conductive polymer composite as bipolar plates for proton exchange membrane fuel cell (PEMFC) were developed by compression molding technique using Polypropylene (PP) as a polymer matrix and Graphite (G), Carbon Black (CB) and Carbon Nanotube (CNTs) as reinforcements. U.S. Department of Energy (US DOE) target values were taken as the benchmark for the development and investigation of thus conductive polymer composite. The effects of CNTs loading on the electrical and mechanical properties of G/CB/PP composite were investigated. By adding small amount of CNTs in to G/CB/PP composite thus will gives synergy effects on both electrical conductivity and mechanical properties. The small amount of CNTs such as I, 1.5, 2, 2.5 and 3 wt% will be added in to G/CB/PP composite. The conductive composite properties were characterized for electrical conductivity, flexural strength, density and shore hardness. The used of CNTs as a third filler of I up to 3 wt% in a G/CB/PP composite resulted in the in-plane electrical conductivity and flexural strength being 618.90 Siem _{and 58.08 MPa respectively. The density and shore hardness of}

v

ABSTRAK

vi

CONTENT

CHAPTER TITLE PAGE

DECLARATION 11

ACKNOWLEDGEMENT iii

ABSTRACT IV

ABSTRAK v

CONTENT VI

LIST OF FIGURE IX

LIST OFT ABLE XI

LIST OF ABBREVIATION AND SYMBOL Xll

LIST OF APPENDIX xm

CHAPTER I INTRODUCTION

I. I BACKGROUND

I.I.I Fuel Cells

l.I.2 Polymer Electrolyte Membrane Fuel Cells 2

1.1.3 Components of fuel cells 3

l.I.4 Bipolar Plate 5

1.2 OBJECTIVES 9

1.3 PROBLEM STATEMENT 9

1.4 SCOPE 10

CHAPTER 2 LITERATURE REVIEW

vii

2.2 ELECTRICALLY CONDUCTIVE 12

THERMOPLASTIC COMPOSITES

2.2.1 Percolation Theory 13

2.3 MATERIALS

2.3.l Fillers

2.3.1.1 Graphite 15

2.3.1.2 Carbon Black 16

2.3.1.3 Carbon Nanotube 18

2.3.2 Polymer

2.3.2. l Polypropylene 20

2.4 PROCESSING METHODS 22

2.4.1 Compression Molding 23

2.4.2 Injection Molding 23

2.5 TESTING METHOD

2.5.1 Electrical Conductivity 25

2.5.2 Mechanical Properties 28

CHAPTER3 METHODOLOGY

3.1 EXPERIMENTAL OVERWIEW 29

3.2 MA TERlALS SELECTION 30

3.3 FABRICATION METHOD

3.3.1 Characterization of Raw Material 30

3.3.2 Pre-Mixing 32

3.3.3 Melt Compounding 34

3.3.4 Pulverize 35

3.3.5 Compression molding 36

3.4 TESTING METHOD

3.4.1 Electrical Conductivity Testing 38

3.4.2 Bulk Density Testing 39

3.4.3 Shore Hardness measurement 40

CHAPTER 4 RESULT AND ANALYSIS

CHAPTERS

4.1 ELECTRICAL CONDUCTIVITY

4.2 FLEXURAL STRENGTH

4.3 BULK DENSITY

4.4 SHORE HARDNESS

DISCUSSION

5.1 ELECTRICAL CONDUCTIVITY

5.2 FLEXURAL STRENGTH

5.3 BULK DENSITY

5.4 SHORE HARDNESS

CHAPTER 6 CONCLUSION AND RECOMMENDATION

6.1 CONCLUSION

6.2 RECOMMENDATION

REFERENCES BIBLIOGRAPHY

APPENDIX A : ASTM C 611 APPENDIX B : ASTM D 790 APPENDIX C : ASTM C 559 APPENDIX D : ASTM C 886

viii

42

44

45

47

49

50

51

52

53

54

56

62

64

66

72

FIGURE 1.1 1.2 1.3 1.4 2.1 2.2 2.3 2.4

2.5

2.6

2.7

2.8

2.9

2.10 2.11 2.12

LIST OF FIGURE

TITLE

Polymer Electrolyte Membrane Fuel Cells (PEMFC)

Schematic

Structure diagram of PEM fuel cell

Photograph of a graphite bipolar plate with flow

channels

Classification of materials for bipolar plates used in

PEM fuel cells

Schematics of percolation pathway

Percolation S-Curve

Agglomerate and Aggregate sizes of Carbon Black

Structures of Diamond, Graphite and Carbon Black

Structure of graphene sheet

Structure of multi walled carbon nanotube and single

walled carbon nanotube

Structural isomers of Carbon Nanotubes, armchair (top)

zig zag (middle), chiral (bottom)

Synthesis of Polypropylene

Structure of Isotactic, Syndiotactic and Atactic

Polypropylene

Compression molding processes for bipolar plates

Injection molding processes for bipolar plates

®Sigracet PPG86 bipolar plates and their production

x

2.13

Four Point _{Probe Technique}

26

2.14

Bulk Density Tester

27

2.15

The set-up of flexural strength of composite bipolar

27

plate

3.1

Flow Chart of the methodology process

29

3.2

(a) Graphite, (b) Carbon Black, (c) Carbon Nanotube,

31

( d) Polypropylene

3.3

Ball milling machine

33

3.4

HAAKE RHEOMIX OS Internal Mixer Machine

35

3.5

Filler with polypropylene

35

3.6

The output of melt compounding process

35

3.7

Centrifugal mill

36

3.8

Mold of sample composite

36

3.9

Hot press machine

37

3.10

Sample of composite G/CB/CNTs/PP

38

3.11

Jandel Multi Four Point _Probe

38

3.12

lnstron Universal Testing Machine

39

3.13

Bipolar plate flexural strength measurement set-up

40

3.14

Electronic Densimeter

40

3.15

Digital Shore Tester

41

4.1

Graph of electrical conductivity (Siem) against weight

43

percentage of CNTs (wt.%) for average result

4.2

Graph of flexural strength (MPa) against weight

44

percentage ofCNT (wt.%)

4.3

Graph of bulk density (g/cm3) against weight percentage

46

of CNT (wt.%)

4.4

Graph of shore hardness against weight percentage of

47

CNT(wt. %)

xi

LIST OFT ABLE

TABLE TITLE PAGE

1.1 Different types of fuel cell 2

1.2 Primary components of a PEM fuel cell 4

1.3 Possible PEM fuel cells bipolar plate materials 8

3.1 Properties ofCNTs, G, CB and PP 31

3.2 The composition of composite G/CB/CNTs/PP (Based on 32

weight%)

3.3 The composition of composite G/CB/CNTs (Based on 33

weight, %)

3.4 The composition of composite G/CB/CNTs (Based on 34

weight g)

4.1 Data of electrical conductivity of the specimens for average 42

result

4.2 Data of flexural strength of the specimens 44

4.3 Data of bulk density of the specimens 45

xii

LIST OF ABBREVIATION AND SYMBOL

PEMFC Polymer Electrolyte Membrane Fuel Cell

HiO Hydrogen

02

Oxygen

MEA Membrane Elecrolyte Assembly

GDL Gas Diffusion Layer

G Graphite

CB Carbon Black

CNTs Carbon Nanotube

pp = Polypropylene

CPCs Conductive Polymer Composites

IPCs Inherently Conducting Polymers SP Es Solid Polymer Electrolytes SWNTs = Single-walled Nanotubes

MWNTs Multi-walled Nanotubes

E Young's Modulus

wt.% Weight Percentage

Siem Siemen/centimeter

cm centimeter

µA micron Ampere

MP a Mega Pascal

mK mili Kelvin

oc

Degree Celcius

NO

A

B

c

D

LIST OF APPENDIX

TITLE

ASTM C611: Standard Test Method for Electrical Resistivity of Manufactured Carbon and Graphite Articles at Room Temperature

ASTM D790: Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials 1

ASTM C559: Standard Test Method for Bulle Density by Physical Measurements of Manufactured Carbon and Graphite Articles 1

ASTM C886: Standard Test Method for Scleroscope Hardness Testing of Carbon and Graphite Materialsl

xiii

PAGE

64

66

72

1

CHAPTERl

INTRODUCTION

1.1 BACKGROUND

1.1.1 Fuel Cells

The concept of fuel cells was first invented by William Grove, a lawyer/scientist in 1839. It have a remarkable potential as low emission power generation sources [1]. This characteristic has been extensively explored through different technologies. He set up a simple experiment where first an electric current is passed through water in order to electrolyze the water into hydrogen and oxygen. Once the hydrogen and oxygen are separated then the power source was replaced with an ammeter. This ammeter showed a current which means that the hydrogen and water were recombining to form water, thus reversing the electrolysis. In a fuel cell, hydrogen gas is combined with oxygen to form water in the reaction is shown below.

2H2

+

02----. 2H20

2

Electrolyte Membrane fuel cells will be discussed further in later sections, because the

research was conducted on materials that can be used in one component of the PEM fuel

cell.

Table I. I: Different types of fuel cell [2]

PEMFC AFC PAFC MCFC SOFC

Type of Electrolyte W _{ions (with OH· ions Wions ｃｾＢＧｩｯｮｳ＠ 0-10ns}

anions bound (typically (H3P04 (typically, (Stabilized

in polymer aqueous KOH solutions) molten ceramic matri: membrane) solution) LiKaC03 with free oxid

eutectics) ions)

Typical cons1roction Plastic, metal Plastic, metal Carbon, High temp Ceramic, high or carbon porous metals, porous temp metals

ceramics ceramic

ln1emal reforming No No No Yes, Good Yes, Good

Temp Match Temp Match

Oxidant Airto ｯｾ＠ Purified Air to Airto Air Air

ｾ＠ Enriched Air

Operational 150- 180°F 190-5000f 370-410°f 1200-1300°F 1350- 1850°F

Temperature (65-85°C) (90-260°C) (190-210°C) (650-700°C) (750-1 OOO°C)

DG System Level 25 to 35% 32 to 4Cl°/o 35 to 45% 40 to 500/o 45 to 55% Efficiency,% HHV

Primary CO, Sultur, CO, ｃｾＮ＠ and co< 1%, SultUr Sultur

Contaminate and NH3 Sulfur Sulfur

Sensitivities

1.1.2 Polymer Electrolyte Membrane Fuel Cells

A polymer electrolyte membrane fuel cell (PEMFC) is a good contender for

portable and automotive propulsion applications because it provides high power density,

solid state construction, high chemical-to-electrical energy conversion efficiency, near

zero environmental emissions, low temperature operation, and fast and easy startup [I].

The PEMFC are fuel cells where the electrolyte is made of an organic polymer that has

the characteristic of a good proton carrier when in presence of a water solution. PEMFC

convert hydrogen and oxygen (or air) into electricity which can be used to power a

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H,0 _ _ _ _ _ _ ___,

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Diffusion Layer

ｾ＠

Heat Platinum----'

Catalyst Proton

Exchange Membrane

Figure I. I : Polymer Electrolyte Membrane Fuel Cells (PEMFC) Schematic [2]

1.1.3 Components of fuel cells

3

Figure 1.2 shows the maJor components m a single PEM fuel cell, which

includes: the membrane electrolyte assembly (MEA) (which is an electrolyte membrane

with catalyst layer on both sides), gas diffusion layers, gaskets, bipolar plates, current

collectors and endplates. There are four main components of PEM fuel cell: Membrane

Electrode Assembly (MEA), Bipolar Plate, End Plate and Current Collector.

Current collector

ｾ＠

<:;,."'°"

Graphite Plate

Graphite Plate

L

Cathode End Plate

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Component Membrane electrode Assembly (MEA) Bipolar plate Endplate Current collector 4

Table 1.2: Primary components of a PEM fuel cell [3]

Material Functionality

Consists of the two electrodes, a membrane electrolyte and two GDLs. The membrane Solid polymer electrolyte separates (with a gas barrier.) the two half-impregnated with catalyst

layers for the anode and cathode

Porous carbon paper or cloth for gas diffusion layer (GDL)

Graphite, stainless steel, or thermoplastic materials

Material with good mechanical strength (normally steel or aluminum)

Metal material with good electric contact and conductivity, normally copper.

cell reactions and allows protons to pass through from anode to the cathode. The dispersed catalyst layers on the electrodes promote each half reaction. The GDL evenly distributes gases to the catalyst on the membrane, conducts electrons from the active area to the bipolar plates and assists in water management.

Distributes gases over the active area of the membrane. Conducts electrons from the anode of one electrode pair to the cathode of next electrode pair. Carries water away from each cell.

Provides integrated assembly for the entire fuel cell stack.

[image:18.516.42.485.81.634.2]

5

1.1.4 Bipolar Plate

The bipolar plate is a major component of the proton exchange membrane (PEM)

fuel cell stack, which takes a large portion of stack cost [ 4, 5]. Bipolar plate, also called

flow field plate or separator plate, is used as an electrical connection between two

electrodes with opposite polarities, thereby implementing the serial addition of the

electrochemical potential of different cells in the fuel cell stack. The bipolar plate is

made of gas-impermeable and electrically conductive material, serving as current

collectors, and forming the supporting structure of the stack. The bipolar plates are

commonly made from graphite, coated metals such as aluminum, stainless steel,

titanium and nickel, or composite plates such as metal or carbon based plates. Gas flow

channels are machined or molded into the plates to provide paths for reactant gases.

Figure 1.3 shows a photograph of a graphite bipolar plate with flow channels for PEM

fuel cell.

Figure 1.3 : Photograph of a graphite bipolar plate with flow channels [3]

The primary functions of bipolar plates include [3 ,4] :

1. The ability to conduct electrons to complete the circuit, including:

Collecting and transporting electrons from the anode and cathode,

[image:19.516.171.342.385.516.2]

6

11. Providing a flow path for gas transport to distribute the gases over the entire

electrode area uniformly

m. Separating oxidant and fuel gases and feeding H2 to the anode and 02 to the

cathode, while removing product water

IV. Providing mechanical strength and rigidity to support thin membrane and

electrodes and clamping forces for the stack assembly; and

v. Providing thermal conduction to help regulate fuel cell temperature and

removing heat from the electrode to the cooling channels.

The requirements for bipolar plates are as follows [3]:

I. Good electrical conductivity(> 100 S cml bulk conductivity),

II. High thermal conductivity (>20Wcml),

iii. High chemical and corrosion resistance,

IV. Mechanical stability toward compression forces,

v. Low permeability for hydrogen,

vi. Low-cost material being processable with mass production techniques,

v11. Low weight and volume, and

viii. Recyclable materials

Two different kinds of materials have been used in the past: metallic and

graphitic. For mobile applications of fuel cells, the requirement of high power densities

at very low cost is difficult to fulfill, though the lifetime in terms of operational hours is

limited to several thousands. Here, stainless steel seems to be the material of choice -the materials already being a mass product, its forming processes are well established in

the automotive industry. Thin metal sheets show sufficient mechanical strength. Two

sheets of thin and structured metal plates can be combined into a bipolar plate with flow

fields on both sides and cooling channels in between. For improving lifetime, a

7

Bipolar plates are a very important component of a fuel cell. They can account for 70-80% of the stack weight and up to 45% of the costs [7]. Bipolar plates have multiple functions in a fuel cell. They are used to distribute the oxygen to the cathode and the hydrogen to the anode, to manage water and heat from the reaction by removing them, provides electrical contact between the plates to carry the current from cell to cell, and to keep the reactants separated. Bipolar plates also need to be made from lightweight, inexpensive materials that can be easily processed when producing bipolar plates.

Bipolar plates can be made from many different materials, such as graphite, metal, or polymer composites with carbon or metal conductive fillers [8]. Graphite is one of the more traditional materials used to produce bipolar plates. The graphite bipolar plates have very good thermal and electrical conductivity, excellent chemical compatibility, and are corrosion resistant. Some problems with graphite bipolar plates are the cost, from machining the gas flow channels into the plate and making the raw graphite, and that graphite has low mechanical strength properties.

Metal bipolar plates have very good electrical and thermal conductivity, good mechanical stability, and can be easily made. The main problem is they are not very resistant to corrosion in the acidic conditions of a fuel cell. Aluminum, titanium, and nickel bipolar plates need to be coated with a protective layer to resist corrosion. Stainless steel is the only metal that has been studied that has the chemical stability to resist corrosion.

8

However, bipolar plate production may eventually shift to injection molding because it

[image:22.516.45.469.184.506.2]

is one of the fastest and least expensive ways to produce plastics.

Table 1.3: Possible PEM fuel cells bipolar plate materials [3]

Types of Materials Properties

Graphite -Impregnate with polymer

-Highly conductive

-Brittle and thick

-High costs for machining flow path

Metals or Metal Alloys -Stainless steel - Al alloys

-Ni-Cr alloy -Ti steel

-Highly conductive

-Corrosion problem

-High cost of machining flow path

Composite Materials -Graphite/ Carbon composite

-Carbon/carbon composite

-Light and low cost

-Low conductivity compare to graphite and metal plate

Conductive Plastics - Liquid Crystal Polymer (e.g. LCP)

BiDOlar plates

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Figure 1.4: Classification of materials for bipolar plates used in PEM fuel cells [3]

1.2 OBJECTIVES

9

The main objectives of this research are to study the effect of Carbon Nanotube (CNT) as a third filler on the properties of Graphite (G), Carbon Black (CB) and Polypropylene (PP) composite in order to improve the electrical conductivity for bipolar plate and also to determine the critical loading of CNT in G/CB/PP composite.

1.3 PROBLEM STATEMENT

10

mechanical and thermal properties. However, to be commercially application of CNTs especially as CPC is limited because of the difficulty to disperse in polymer matrices. Thus, because CNTs are non-polar materials containing only a few functional groups that could react with polymers. Therefore, nowadays there are different methods have been developed to achieve stronger interaction between CNTs and polymers metrics. But high filler loading of CNTs may cause a substantial reduction in electrical conductivity, strength and ductility of thus composite as bipolar plate, and resulting in difficulty in making thin plates associated with high stack power densities. In order to overcome this problems, using small amount of CNTs (I up to 3 wt°/o) in multi filler composition and through pre mixing process using ball mill of all filler materials could be an alternative process to produce G/CB/CNTs/PP composite as bipolar plate.

1.4 SCOPE