STUDIES ON CARBON/CARBON COMPOSITE BIPOLAR PLATE FOR PEM FUEL CELL IN AEROSPACE APPLICATION THAKUR SUDESH KUMAR RAUNIJA DEPARTMENT OF CHEMICAL ENGINEERING INDIAN INSTITUTE OF TECHNOLOGY DELHI May 2017
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STUDIES ON CARBON/CARBON COMPOSITE
BIPOLAR PLATE FOR PEM FUEL CELL IN
AEROSPACE APPLICATION
THAKUR SUDESH KUMAR RAUNIJA
DEPARTMENT OF CHEMICAL ENGINEERING
INDIAN INSTITUTE OF TECHNOLOGY DELHI
May 2017
©Indian Institute of Technology Delhi (IITD), New Delhi, 2017
STUDIES ON CARBON/CARBON COMPOSITE
BIPOLAR PLATE FOR PEM FUEL CELL IN
AEROSPACE APPLICATION
by
THAKUR SUDESH KUMAR RAUNIJA
submitted
in partial fulfillment of the requirement of the degree of Doctor of Philosophy
to the
DEPARTMENT OF CHEMICAL ENGINEERING
INDIAN INSTITUTE OF TECHNOLOGY DELHI
May 2017
Dedicated to
“My late grandmother Mrs. Shaanti Devi and my kidney failure
younger sister Ms. Seema Rani who were the real propeller in the
completion of this piece of work”
Statement
The thesis ‘Studies on Carbon/Carbon Composite Bipolar Plate for PEM Fuel Cell in
Aerospace Application’ is my original work carried out by me at Vikram Sarabhai Space
Centre, Indian Space Research Organisation, Thiruvananthapuram, Kerala, India and Indian
Institute of Technology Delhi, Hauz Khas, New Delhi, India under the supervision of Dr.
S.C. Sharma, Deputy Director, Vikram Sarabhai Space Centre and Dr. Anil Verma, Associate
Professor, Department of Chemical Engineering, Indian Institute of Technology Delhi. I
certify that no conflict of interest in any form is associated with the present work. Further, it
is not presented in any R&D lab and institute for claiming any degree or diploma. I also
certify that the details and information taken from the works of other investigators have been
acknowledged in the thesis.
Thakur Sudesh Kumar Raunija
Certificate
This is certified that the work contained in the thesis entitled ‘Studies on Carbon/Carbon
Composite Bipolar Plate for PEM Fuel Cell in Aerospace Application’ by Thakur
Sudesh Kumar Raunija for the award of the degree of Doctor of Philosophy has been
carried out under our supervision.
The results contained in this thesis have not been submitted, in part or in full, to any other
university or institute for the award of any degree or diploma.
(Dr. S.C. Sharma) (Dr. Anil Verma)
Deputy Director Associate Professor
Vikram Sarabhai Space Centre Department of Chemical Engineering
Indian Space Research Organisation Indian Institute of Technology Delhi
Thiruvananthapuram-695022 New Delhi-110016
India India
Preface
Proton exchange membrane (PEM) fuel cell is best suitable in aerospace application due to
quick start-up, and low temperature and pressure operations. The bipolar plate is the key
constituent of PEM fuel cell, which accounts for around 80% weight and almost all of the
volume of a fuel cell. The present thesis describes the development of a novel method to
rapidly make carbon/carbon (C/C) composite, and fabrication of bipolar plate therefrom
followed by functional testing of bipolar plate. The entire work was divided into seven
chapters.
Chapter 1 gives an introduction about fuel cell, emergence of fuel cell, usage of fuel cell,
types of fuel cell, working principle of PEM fuel cell, constituents of PEM fuel cell, functions
of main constituent i.e. bipolar plate of PEM fuel cell, materials used for the fabrication of
bipolar plate, and comparative analysis of advantages and disadvantages of different
materials.
Chapter 2 presents comprehensive literature survey to establish the problem. As part of
literature survey, the fundamental aspects of carbon is presented initially, and thereafter a
brief review on the carbon reinforcement and carbon matrix precursor is presented. Further,
the types of carbon composite, its processing methodologies and properties are briefed. The
same is followed by the detailed review of carbon/carbon (C/C) composite. In later part of the
chapter, the usage of C/C composite for the fabrication of bipolar plate and its present
scenario is discussed. At the end of the chapter, objectives of the present research work are
defined.
viii
Chapter 3 describes about the raw materials used in the processing of C/C composite at the
beginning. The details of pre-processing of reinforcement by chopping and exfoliation, and
synthesis and stabilization of primary matrix precursor (PMP) are presented thereafter.
Further, the characterization techniques to check the suitability of pre-processed raw
materials are briefed. The same is followed by a brief description about the processing of C/C
composite and detailed description of the characterization techniques along with standard test
methods. Further, brief description of bipolar plate fabrication and detailed methodology for
the system level testing of C/C composite bipolar plate through composite stability test,
corrosion current test and fuel cell testing are presented at the end of the chapter.
Chapter 4 deals with detailed experimental work carried out to rapidly develop C/C
composite by novel way of two-steps processing. In the first step, C/C composite is made by
high pressure hot-pressing (HP) method comprising of mixing, moulding, drying, hot-
pressing and carbonization. During HP method, various key parameters like hot-pressing
pressure and heating rate, reinforcement loading, temperature and time shifts, and matrix
precursor modification are studied in detail through visual and SEM analysis, density,
mechanical properties, yield, yield rate and yield impact. In second step, the densification of
C/C composite obtained from HP method is carried out using secondary matrix precursor
(SMP) through low pressure impregnation-thermosetting-carbonization (ITC) method. The
impact of HP method parameters on the densification is studied in detail through visual and
SEM analysis, density, porosity, mechanical properties, and permeability analysis.
Chapter 5 describes the processing of C/C composite of size 125 mm × 125 mm × 20 mm
based upon the optimum processing parameters obtained in Chapter 4. Later, description
about the fabrication of C/C composite bipolar plate of size 95 mm × 95 mm × 3.5 mm using
ix
conventional grinding, wire electron discharge machining, and milling is presented. Further,
post fabrication inspection of bipolar plate flow field channels through SEM analysis is
discussed. The results of system level testing of C/C composite bipolar plate obtained through
composite stability test, corrosion current measurement, and fuel cell testing are presented
and discussed. At the end of the chapter, the comparative analysis of fuel cell results of C/C
composite bipolar plate with graphite bipolar plate is made.
In strategic application of the fuel cell, the weight and volume requirements are more
stringent along with electrical conductivity and mechanical strength. Hence, the bipolar plate,
which accounts for 80 wt% and almost all of the fuel cell volume, should be very thin with
lowest permissible density. Thus, new bipolar plate system of carbon/carbon (C/C) composite
was studied in detail and presented in the major portion of this thesis. However, the ever
sought demand of developing a bipolar plate system with very high specific strength for
strategic sector made us to explore new system. Coincidently, the idea of ultra-thin (net
thickness ≤ 0.25 mm) bipolar plate was evolved while working on the development of wire
electron discharge machineable (EDM) carbon/silicon carbide (C/SiC) composite for air
breathing propulsion engine of a launch vehicle. The need for the development of rugged and
very thin bipolar plate made us to explore this system with ceramic matrix and carbon
reinforcement for bipolar plate application. It is the first time when ceramic and carbon
composite is being reported as bipolar plate material. The preliminary results on this system
are presented in Chapter 6.
The studies carried out on C/C composite bipolar plate for PEM fuel cell in aerospace
application and next generation C/SiC composite bipolar plate system are concluded in
Chapter 7 with key results. The future scope of the work in the field is also briefed in this
x
chapter. It will be of much help for the buddy researchers to formulate their objectives in the
area of bipolar plate.
Thakur Sudesh Kumar Raunija
Acknowledgements
In 2008, at Vikram Sarabhai Space Centre (VSSC) after completion of all joining formalities
when I reported to Mr. S. Babu, Head (Retd.), CCL/VSSC, his second question was – When
are you planning your higher studies? That was the real ignition of the fire for higher studies.
But the real journey in this direction started when I got an opportunity to pursue PhD at IIT
Guwahati as an external candidate of VSSC. Now, the wonderful journey is going to end with
flying colors. Before, I conclude my journey full of knowledge and experience gained from
various prominent personalities, I should give the due credit to the persons and the
personalities who backed this journey in various capacities.
The process of acknowledgement starts with Dr. S.C. Sharma, Deputy Director, VSSC who
encouraged me to pursue direct PhD after B.E. He provided all the necessary support for
completion of PhD. The next person to be thanked is Mr. C. Simon Wesley, Head (Retd.),
AMCD/VSSC who encouraged and helped me in arranging necessary support from VSSC for
attending interview at IIT Guwahati, and joining at IIT Guwahati thereafter. The support
provided by Dr. Koshy M. George, Dy. Director (Retd.), VSSC is highly acknowledgeable.
The kind and timely approvals of Academic Committee, VSSC for joining PhD programme
at IIT Guwahati and transfer of registration from IIT Guwahati to IIT Delhi in concurrence
with the movement of Dr. Anil Verma is greatly acknowledgeable.
I like teaching profession and consider it the effective tool for the transformation of the
society. This was one of the reasons to pursue PhD so that I can become the part of this
profession along with services to Indian Space Research Organisation. And the one and only
one person, who made my reason right, grew a great interest towards this profession, taught
xii
me the real approach of a great teacher, is none other than Dr. Anil Verma. The lessons learnt
from him and his experiences are unforgettable. I learnt many things from him, but his
straightforwardness and supportive nature are the most influential qualities, I tried to learn
from him. The all-time support received from Dr. Anil Verma is immense and incredible. To
him, I owe my gratitude and deepest appreciation for nurturing this educational experience.
Because of his sincere commitment to my educational and personal well-being both at IIT
Guwahati and IIT Delhi, I can truly consider myself a better person and student.
I would like to thank some other personalities from IIT Guwahati. They include Dr. Pankaj
Tiwari, Dr. V. V. Goud, Dr. Pallav Ghosh, Dr. Vimal Katiyar, Dr. Chandan Das and Dr. V. S.
Mohalkar, my course instructors during my course work at IIT Guwahati. Their excellent
teaching and kind support helped me to clear all the six subjects in a single semester with
flying colors. Further, I would like to express my gratitude to Doctoral Research Committee
members; Dr. Chandan Das, Dr. V. V. Goud and Dr. A.K. Maurya for their help and
guidance at IIT Guwahati.
Additionally, I must acknowledge several individuals at IIT Guwahati for their kind support
in various capacities including Dr. Avijit Ghosh, Dr. Leela Manohar Ashleela, Dr. Surya
Singh, Dr. Rajeev Parmar, Dr. Sankar Chakma, Mr. Sunny Kumar, Mr. Preetam Kumar Dixit,
Ms. Sanjukta Bhoi, Ms. Cherukuri Jayalakshmi (Late), Mr. Fahad and my dear disciple Mr.
Anoop Sharma.
The process of acknowledgement dawns at IIT Delhi. The immense support given by Mr.
Karan Malik and Mr. Sonit Balyan in accommodating me on several occasions, and giving
the memorable company whenever I made the visit to IIT Delhi. The company and the
xiii
technical support rendered by Dr. Rajeev Kumar Gautam are un-forgettable and un-
countable. The support of my other lab mates and neighboring-lab mates; Ms. Vaishali
Sharma, Mr. Kalpak, Mr. Pranjal, Mr. Manav, Mr. Himaghana, Ms. Shephali Singh, Ms.
Rajbala, Ms. Arkadeepa Bayal, Mr. Arvind Kumar, Mr. Sanjay Singh is highly
acknowledgeable. The all-time presence of my disciple Mr. Anoop Sharma even at IIT Delhi
was more than enough to utilize my free and boring time for quality spiritual discussions.
Those discussions were really the propelling boosters in completing this piece of work.
The immense support and guidance provided by Doctoral Research Committee members
(Prof. S. Basu, Dr. M. Ali Haider, and Dr. Dibakar Rakshit) at IIT Delhi is highly
accoladeable.
I would like to specially thank Mr. Vineeth, Mr. Omendra Mishra, Mr. Mukesh Bhai, Mr.
Hentry and Ms. Bindhu for their kind assistance in carrying out the experiments.
The acknowledgment is due to Dr. Neeraj Naithani, Ms. Supriya, Ms. Soumaya Mol, Mr.
Rakesh Ranjan, Mr. Abhilash, Ms. Bismi Basheer, Dr. Bina Korah Catherine, Mr. Vijendra
Kumar, Dr. P. Rameshnarayana, Dr. S. V. S. Narayan Murthy, Dr. Arjunan Venugopalan,
Mr. Rahul Ghosh, Mr. Sushant K. Manwatkar, Ms. Dhanya, Mr. Ranjith, Mr. Manikandan,
Mr. Sisupalan, Mr. Gundi Sudarsan Rao, Mr. K. Saravanan, Mr. J. Srinath, Mr. B. Masin and
Dr. H. Sreemoolanadhan for their kind support in the characterization of C/C composite.
The system level testing of C/C composite bipolar plate carried out by Mr. M. Shaneeth and
his team members (Mr. Samrat Deb Choudhary, Mr. Vinay Mohan Bhardwaj, Mr. Surajeet
Mohanty and Mr. P. Nandikesan) at Fuel Cell Laboratory/VSSC is highly acknowledgeable.
xiv
The support rendered by Mr. G. P. Khanra, Ms. Mariamma Mathew, Dr. Bhanu Pant, Dr.
Govind, Dr. S Ilangovan and Dr. V Sekkar in reviewing the manuscripts and giving several
technical inputs is greatly acknowledged.
The mental support provided by Dr. R. Suresh Kumar during my initial phase at VSSC is
highly acknowledgeable. The motivation given by Dr. V. M. J. Sharma which became a
propelling factor in the speedy completion of this work is also highly acknowledgeable. At
last not the least, I thank almighty for giving wisdom and strength to successfully complete
this piece of work inspite of all hardships.
Thakur Sudesh Kumar Raunija
Abstract
Polymer electrolyte membrane (PEM) fuel cell is preferred over others for space applications
because of quick start-up, high efficiency, high power density, and low temperature
and pressure operations. Bipolar plate (BP) is one of the key constituents, which
accounts for around 80% weight and almost all of the volume of a fuel cell stack. Therefore,
the material used for its fabrication should be light in weight, strong enough to
withstand natural and induced environment, and show excellence in performance. High
specific energy (kW/kg) and durability are the mission requirement of spacecraft power
system. Almost all of the conventional materials (graphite, metal, and carbon/polymer
composite) used for its fabrication are associated with one or more problems, and the
necessity to explore a material for the bipolar plate used in aerospace application arises.
Carbon/carbon composite, which was first synthesised for thermo-structural applications,
possesses all the necessary properties. However, the time consuming and high
temperature processing of C/C composite are the major technical challenges, which are
to be addressed. In the present work, a novel methodology for the rapid and effective
fabrication of C/C composite bipolar plate is presented. The fabrication of C/C composite
was carried out using exfoliated carbon fibers as reinforcement, wherein carbon matrix was
derived from mesophase pitch and phenolic resin using high pressure hot-pressing (HP)
method and low pressure impregnation thermosetting carbonization (ITC) method. The
uniquely designed methodology explored for rapid fabrication could produce C/C
composite in a very short time of 137 h as compared to 3-4 months in conventional
processes while using a pressure not more than 25 MPa in any processing stage. The
C/C composite thus obtained offered bulk density 1.75 g/cm3, impact strength 4.8 kJ/m
2,
tensile strength 45 MPa, flexural strength 98 MPa, compressive strength 205 MPa,
xvi
electrical conductivity 190 (through-plane) & 595 S/cm (in-plane), and thermal
conductivity 24 (through-plane) & 51 W/mK (in-plane). The bipolar plate of 95 mm × 95 mm
× 3.5 mm with serpentine channels of 1 mm width and 1 mm depth fabricated out of the C/C
composite made through rapid and effective methodology was tested in PEM fuel cell and
compared with graphite bipolar plate. The performance of C/C composite bipolar plate cell in
the ohmic polarization dominated region was found similar to that of graphite bipolar plate.
However, voltage difference of around 0.05 V at maximum power density was obtained at
65oC. Further, the cell with C/C composite bipolar plate at an operating temperature of 65
oC
showed a voltage as high as 0.3 V for a current density of 1100 mA/cm2
along with a power
density as high as 370 mW/cm2. The detailed characterization and evaluation of the C/C
composite bipolar plate in fuel cell showed promising results for its utilization in the
next generation PEM fuel cell used in aerospace applications. While working on the
development of wire EDM machineable C/SiC composite for space application, the idea of
making ultrathin (net thickness ≤ 0.25 mm) bipolar plate was evolved, which encouraged us
to explore this system for bipolar plate application apart from C/C composite. It is the first
time when carbon reinforced silicon carbide composite is being reported as bipolar
plate material. Therefore, at the end of the thesis, the preliminary results carried on
the development of C/SiC composite and fabrication of bipolar plate are presented.
Keywords: Bipolar plate, Carbon/carbon composite, Carbon fiber, Fuel cell testing, HP
method, ITC method, Matrix precursor, PEM fuel cell.
xvii
पॉलीमर इलकटरोलाइट झिलली ईधन सल को तवररत सटाटट-अप, उचच दकषता, उचच शककटत घनतव और
ननमन तापमान और दबाव सचालन क कारण अतररकष अनपरयोगो क ललए दसरो की तलना म पसद
ककया जाता ह। दववधरवी पलट इसका एक मखय घटक ह, जो ईधन सल सटक क कल वजन और
आयतन का लगभग 80% हहससा होती ह। इसललए, इसक ननमाटण क ललए इसतमाल ककया जान वाला
पदारट वजन म हलका होना चाहहए, पराकनतक और परररत पयाटवरण का सामना करन क ललए पयाटपत
मजबत होना चाहहए, और परदशटन म उतकषट होना चाहहए। उचच ववलशषट ऊजाट (kW/kg) और
सरानयतव अतररकष यान की लमशन आवशयकता होती ह। इसक ननमाटण क ललए उपयोग की जान वाली
लगभग सभी परपरागत सामगरी (गरफाइट, धात और काबटन/पॉललमर लमशरित) एक या एक स अशरधक
समसयाओ स जडी होती ह। इसललए अतररकष अनपरयोग म इसतमाल योगय दववधरवी पलट क ललए एक
नतन सामगरी का पता लगान की आवशयकता ह। काबटन/काबटन लमशरित, जो पहल रमाटमीटरो-
सरचनातमक अनपरयोगो क ललए सशलवित रा, सभी आवशयक गणो क पास ह हालाकक, काबटन/काबटन
लमशरित बनान म लगन वाला समय और उचच तापमान परससकरण परमख तकनीकी चनौनतया ह,
कजनह सबोशरधत ककया जाना ह। वतटमान कायट म, काबटन/काबटन लमशरित दववधरवी पलट क तज और
परभावी ननमाटण क ललए एक उपनयास पदधनत परसतत की गई ह। काबटन/काबटन लमशरित का ननमाटण
सदढीकरण क रप म एकटसफोइएटड काबटन फाइबर का उपयोग करक ककया गया ह, कजसम काबटन
महरकटस मसॉकफस वपच और उचच दबाव गमट दबाव (एचपी) ववशरध और कम दबाव ससचन रमोसहटग
काबटननाइजशन (आईटीसी) पदधनत का उपयोग करक फनोललक राल स बनाई गई ह। तजी स
फबरिकशन क ललए खोज की गई ववलशषट पदधनत स 137 घट क बहत ही कम समय म और ककसी
भी परससकरण चरण म 25 एमपीए स अशरधक दबाव का उपयोग ककय बरबना, काबटन/काबटन लमशरित का
उतपादन ककया गया ह, जो पारपररक परकियाओ म लगन वाल 3-4 महीन क समय की तलना म बहत
ही कम ह। इस परकार परापत काबटन/काबटन लमशरित का रोक घनतव 1.75 g/cm3, परभाव शककटत 4.8
kJ/m2, तनयता ताकत 45 MPa, फलकटसरल ताकत 98 MPa, सपीडन ताकत 205 MPa, ववदयत
xviii
चालकता 190 (ववमान क माधयम स) और 595 S/cm (ववमान म), और रमटल चालकता 24 (ववमान
क माधयम स) और 51 W/mK (ववमान म) पाई गई। 95 mm × 95 mm × 3.5 mm की दववधरवी पलट
1 mm चौडाई और 1 mm की गहराई क सााप चनल क सार तीवर और परभावी पदधनत क माधयम स
बनाय गए काबटन/काबटन लमशरित स बनाई गई और ईधन सल म इसका परीकषण ककया गया। ओलमक
धरवीकरण वाल कषतर म, काबटन/काबटन लमशरित की दववधरवी पलट का परदशटन गरफाइट की दववधरवी पलट
क समान पाया गया। अशरधकतम बरबजली घनतव पर 65oC क तापमान पर लगभग 0.05 V का वोलटज
अतर पाया गया ककया गया। इसक अलावा, 65oC क ऑपरहटग तापमान पर ईधन सल न
काबटन/काबटन लमशरित दववधरवी पलट क सार 1100 mA/cm2 क करट घनतव क सार सार 370
mW/cm2 क पावर घनतव पर 0.3 V जयादा वोलटज हदखाई। ईधन सल म काबटन/काबटन लमशरित
दववधरवी पलट का ववसतत लकषण वणटन और मलयाकन करन क बाद अतररकष अनपरयोगो म उपयोग
की जान वाली अगली पीढी की ईधन सल म इसक उपयोग क ललए अचछ पररणाम हदखाई हदए।
अतररकष अनपरयोगो क ललए तार ईडीएम मशीनक काबटन/लसललकॉन काबाटइड लमशरित का ववकास करत
हए, अलराशररन (नट मोटाई ≤ 0.25 लममी) दववधरवी पलट बनान का ववचार ववकलसत हआ, कजसन हम
काबटन/काबटन क अलावा दववधरवी पलट अनपरयोग क ललए इस परणाली का पता लगान क ललए
परोतसाहहत ककया। यह पहली बार ह जब काबटन परबललत लसललकॉन काबाटइड लमशरित दववधरवी पलट
सामगरी क रप म सशरचत ककया जा रहा ह। इसललए, रीलसस क अत म, काबटन/लसललकॉन काबाटइड
लमशरित क ववकास और दववधरवी पलट क ननमाटण पर परारलभक पररणाम परसतत ककए गए ह।
कीवरडस: दववधरवी पलट, काबटन/काबटन लमशरित, काबटन फाइबर, ईधन सल परीकषण, एचपी ववशरध, आईटीसी
ववशरध, महरकटस अगरदत, पीईएम ईधन सल।
List of Tables
Table 1.1 Salient features of fuel cells 6
Table 1.2 Target properties set by DOE for bipolar plate to achieve
by 2017
10
Table 2.1 Typical range of properties for C/C composite 41
Table 3.1 Properties of carbon fiber 56
Table 3.2 Properties of secondary matrix precursor (SMP) 56
Table 4.1 Properties of mesophase pitch stabilized for 1, 5 and 20 h,
and compared with unstabilized mesophase pitch (0 h)
90
Table 4.2 Influence of hot-pressing pressure on the densification and
microstructure for 50 wt% reinforcement, and 0.5oC/min
heating rate
97
Table 4.3 Properties of the compacts for 50 wt% reinforcement, and
0.5oC/min heating rate
98
Table 4.4 Influence of heating rate on the densification and
microstructure for 50 wt% reinforcement, and 15 MPa
pressure
101
Table 4.5 Properties of the compacts for 50 wt% reinforcement, and
15 MPa pressure
103
Table 4.6 Influence of reinforcement loading on the densification and
microstructure for 15 MPa pressure, and 0.2°C/min heating
rate
106
Table 4.7 Properties of the compacts for 15 MPa pressure, and
0.2°C/min heating rate
107
xx
Table 4.8 Influence of densification cycles (DC) on the density of the
compacts
113
Table 4.9 Influence of densification cycles (DC) on the porosity of
the compacts
114
Table 4.10 Total processing time and mechanical properties of the
compacts
114
Table 4.11 Density, yield, processing time, yield rate, yield impact and
mechanical properties of the compacts
128
Table 4.12 Density, yield, processing time, yield rate, yield impact,
and mechanical properties of the compacts
128
Table 5.1 Properties of C/C composite bipolar plate in comparison
with commercial graphite plate
141
Table 6.1 Properties of C/SiC composite bipolar plate in comparison
with C/C composite bipolar plate
154
List of Figures
Fig.1.1 Schematic of PEM fuel cell 7
Fig.2.1 Phase diagram of carbon 32
Fig.2.2 Resole structure 36
Fig.2.3 C/C composite manufacturing routes 39
Fig.3.1 Fiber milling machine: a) schematic; b) photograph 57
Fig.3.2 Schematic of fiber exfoliation set-up 59
Fig.3.3 Flow chart for synthesising primary matrix precursor (PMP) 60
Fig.3.4 Tensile test specimen: a) drawing; b) photograph 69
Fig.3.5 Gas permeability tester: a) schematic; b) photograph 75
Fig.3.6 Bipolar plate under test in PEMFC 78
Fig.4.1 Flow chart for C/C composite processing: 1) HP method; 2) ITC
method
84
Fig.4.2 Die system (70 mm × 50 mm) for making green cake 85
Fig.4.3 Hot-press used to make compact 86
Fig.4.4 Carbonization furnace: a) schematic; b) photograph 87
Fig.4.5 Resin impregnation equipment: a) schematic of impregnation
chamber; b) photograph
88
Fig.4.6 FTIR spectrum of the pitch samples stabilized for 5 h and 20 h,
and compared with unstabilized pitch (0 h): a) 0 h; b) 5 h; c) 20 h
91
Fig.4.7 TGA of pitch samples 92
Fig.4.8 Matrix precursor and reinforcement interaction in conventional
processes
94
Fig.4.9 Matrix precursor and reinforcement interaction in the present
xxii
work 94
Fig.4.10 SEM micrographs of the compacts: a) HP10; b) HP15 97
Fig.4.11 Yield behaviour of PMP as a function of pressure 100
Fig.4.12 Yield rate and yield impact of PMP as a function of pressure 100
Fig.4.13 Photograph of the compacts: a) HR3.3; b) HR1.0 101
Fig.4.14 SEM micrographs of the compacts: a) HR0.5; b) HR0.3; c) HR0.2;
d) HR0.1
103
Fig.4.15 Yield of PMP as a function of heating rate 104
Fig.4.16 Yield rate and yield impact of PMP as a function of heating rate 105
Fig.4.17 SEM micrographs of the compacts: a) R70; b) R50; c) R30 106
Fig.4.18 Yield, yield rate and yield impact of PMP as a function of
reinforcement loading
108
Fig.4.19 FESEM micrographs of the compacts: a) HP10; b) HP15; c) HR0.3;
d) HR0.2; e) HR0.1; R70 after three densification cycles
110
Fig.4.20 Schematic of pore filling mechanism during low pressure ITC
method
112
Fig.4.21 SEM micrographs of fracture surfaces: a) HP15; b) HR0.3; c)
HR0.2; d) HR0.1
119
Fig.4.22 Schematic of slicing of test specimens from bulk compact for
permeability measurement
120
Fig.4.23 Representation of high pressure HP method process plan: a) hot-
pressing; b) carbonization [axes are not in scale]
122
Fig.4.24 SEM micrographs of the compacts: a) HR0.2; b) IS-T 124
Fig.4.25 Temperature, pressure and height vs time profile during hot-
pressing (black line: temperature; blue line: pressure; green line:
xxiii
compact height) 125
Fig.4.26 SEM micrographs of the compacts: a) HR0.2; b) IS-T 126
Fig.4.27 Representation of revised process plan of HP method (hot-
pressing) [axes are not in scale]
130
Fig.5.1 Die system (125 mm × 125 mm): a) top punch; b) main cavity; c)
assembled die
136
Fig.5.2 SEM micrographs of C/C composite: a) through-plane and b) in-
plane after HP method; c) through-plane and d) in-plane after ITC
method
138
Fig.5.3 Photograph of C/C composite bipolar plate (95 mm × 95 mm ×
3.5 mm)
140
Fig.5.4 SEM micrographs of C/C composite bipolar plate: a) rib; b)
channel; c) higher magnification of rib; d) higher magnification of
channel
142
Fig.5.5 I-V performance and power density of C/C composite bipolar
plate in-comparison with graphite bipolar plate at 35oC
143
Fig.5.6 I-V performance and power density of C/C composite bipolar
plate in-comparison with graphite bipolar plate at 45oC
143
Fig.5.7 I-V performance and power density of C/C composite bipolar
plate in-comparison with graphite bipolar plate at 55oC
144
Fig.5.8 I-V performance and power density of C/C composite bipolar
plate in-comparison with graphite bipolar plate at 65oC
144
Fig.6.1 Schematic of C/SiC composite preparation 150
Fig.6.2 XRD pattern of the compact F50 153
Fig.6.3 SEM micrographs of the compact F50: a) side surface; b) top
xxiv
surface 155
Fig.6.4 Photographs of C/SiC composite bipolar plates (40 mm × 40
mm): a) F30; b) F50 (arrows show the chipping of channels and
ribs surfaces)
156
Fig.6.5 Schematic of crack hindering due to various loading of carbon
fiber in the compact
157
List of Acronyms
Thermal diffusivity (cm2/s)
Specific enhancement in compressive strength (MPa/h)
Specific enhancement in flexural strength (MPa/h)
Actual porosity of the compact after n densification cycles (%)
Porosity of the compact after HP method (%)
Theoretical porosity of the compact after n densification cycles (%)
Permeability for definite thickness and pressure at constant temperature
(cm3/cm
2s)
Specific compressive strength after HP method (MPa)
Specific compressive strength after ITC method (MPa)
Specific flexural strength after HP method (MPa)
Specific flexural strength after ITC method (MPa)
Bulk density (g/cm3)
Bulk density of the compact after HP method (g/cm3)
Maximum possible density of PCM after HP method (g/cm3)
Density of SCM (g/cm3)
Bulk density of the compact after n densification cycles (g/cm3)
Density of reinforcement (g/cm3)
Density of SMP (g/cm3)
Theoretical density of the compact after HP method (g/cm3)
Contact area (cm2)
Compressive strength after HP method (MPa)
xxvi
Compressive strength after ITC method (MPa)
Specific heat (J/gK)
Electrical conductivity (S/cm)
Flexural strength after HP method (MPa)
Flexural strength after ITC method (MPa)
Thermal conductivity (W/mK)
Length of the sample (cm)
Number of densification cycles
Resistance (Ω)
Ra Arithmetic means of roughness values
Test duration (s)
Total process time till HP method (h)
Total process time till ITC method (h)
Volume fraction of PCM in compact after HP method
Volume fraction of reinforcement in compact after HP method
Volume of PCM in compact after HP method (cm3)
Volume of reinforcement in compact after HP method (cm3)
Volume of the compact (cm3)
Volume of gas permeates during test (cm3)
Weight of the compact (g)
Weight of sample after stabilization (g)
Weight of sample before stabilization (g)
Weight of the compact after HP method (g)
Weight of PCM in compact after HP method (g)
xxvii
Weight of PMP taken initially (g)
Weight loss of PMP during vacuum moulding (g)
Weight of reinforcement in the compact after HP method (g)
Weight of reinforcement taken initially (g)
Weight loss of reinforcement during processing (g)
Yield impact (%)
Yield of PMP (%)
Yield rate (%/h)
Yield of SMP (%)
Densification efficiency (%)
Overall liquid (SMP) impregnation efficiency (%)
AFC Alkaline fuel cell
BP Bipolar plate
C/C Carbon/carbon
CCL Carbon and ceramics laboratory
C/P Carbon/polymer
C/SiC Carbon/silicon carbide composite
CHN Carbon hydrogen nitrogen
CHNS Carbon hydrogen nitrogen sulphur
CNT Carbon nanotube
CTP Coal tar pitch
CVD Chemical vapor deposition
CVI Chemical vapor infiltration
DC Densification cycle
xxviii
DMFC Direct methanol fuel cell
DOE Department of energy
EDM Electron discharge machining
FESEM Field emission scanning electron microscope
FTIR Fourier transform infrared
GDL Gas diffusion layer
GE General electric
HIP Hot isostatic pressing
HIPIC Hot isostatic pressure impregnation carbonization
HP Hot-pressing
HSXD High speed xenon discharge
HTT Heat treatment temperature
ISRO Indian space research organisation
ITC Impregnation-thermosetting-carbonization
K Group of 1000 filaments
LPI Liquid phase impregnation
MCFC Molten carbonate fuel cell
MEA Membrane electrode assembly
MWCNT Multi wall carbon nanotube
NASA National aeronautics and space administration
OMG Oxygen mass gain
PAFC Phosphoric acid fuel cell
PAN Polyacrylonitrile
PCM Primary carbon matrix
PEEK Polyether ether ketone
xxix
PEI Polyethylene imine
PEM Proton exchange membrane
PEMFC Proton exchange membrane fuel cell
PI Polyimide
PMP Primary matrix precursor
PP Petroleum pitch
PR Phenolic resin
SCM Secondary carbon matrix
SEM Scanning electron microscope
SMP Secondary matrix precursor
SOFC Solid oxide fuel cell
SWCNT Single wall carbon nanotube
TGA Thermogravimetric analysis
vol Volume
VSSC Vikram sarbhai space centre
wt Weight
XRD X-ray diffraction
Content
Statement iii
Certificate v
Preface vii
Acknowledgment xi
Abstract xv
List of Tables xix
List of Figures xxi
List of Acronyms xxv
Content xxxi
Chapter 1: Introduction
1.1. Preamble
1.2. Fuel Cell
1.3. Types of Fuel Cell
1.4. Working Principle of PEM Fuel Cell
1.5. Constituents of PEM Fuel Cell
1.6. Bipolar Plate
References
1-21
3
4
5
7
8
10
15
Chapter 2: Literature Review
2.1. Preamble
2.2. Carbon
2.2.1. Carbon Fiber
2.2.1.1. Structure of carbon fiber
2.2.1.2. Manufacturing of carbon fiber
23-52
25
25
29
31
32
xxxii
2.2.1.3. Types of carbon fiber
2.2.2. Carbon matrix precursor
2.3. Carbon Composite
2.4. Carbon/Carbon Composite as Bipolar Plate
2.5. Summary of the Literature Review
2.6. Objectives of the Present Work
References
33
34
36
42
44
44
45
Chapter 3: Materials and Methods
3.1. Preamble
3.2. Raw Materials
3.3. Pre-processing of Raw Materials for Composite
3.4. Characterization of Raw Materials
3.4.1. Average particle size
3.4.2. Softening point
3.4.3. CHN analysis
3.4.4. Oxygen mass gain
3.4.5. FTIR
3.4.6. Thermogravimetric analysis
3.5. Composite Preparation
3.6. Composite Characterization
3.6.1. Yield
3.6.2. Density measurement
3.6.3. Yield rate and yield impact
3.6.4. Densification efficiency
3.6.5. Porosity determination
53-79
55
55
56
61
61
61
62
62
62
63
63
63
63
64
66
67
68
xxxiii
3.6.6. XRD
3.6.7. Morphology
3.6.8. Tensile strength
3.6.9. Flexural strength
3.6.10. Compressive strength, modulus and Poison’s ratio
3.6.11. Impact strength
3.6.12. Surface roughness
3.6.13. Hardness
3.6.14. Thermal conductivity
3.6.15. Coefficient of thermal expansion
3.6.16. Electrical conductivity
3.6.17. Helium gas permeability
3.7. Bipolar Plate Fabrication
3.8. System Level Testing
3.8.1. Composite stability test
3.8.2. Corrosion current
3.8.3. Fuel cell testing
3.9. Summary of the Chapter
References
69
69
70
70
70
72
72
73
73
74
74
74
75
76
76
76
77
78
79
Chapter 4: Development of Carbon/Carbon Composite
4.1. Preamble
4.2. Processing of Carbon/Carbon Composite
4.2.1. High pressure HP method
4.2.2.1. Mixing
4.2.1.2. Moulding
81-132
83
83
85
85
85
xxxiv
4.2.1.3. Drying
4.2.1.4. Hot-pressing
4.2.1.5. Carbonization
4.2.2. Low pressure ITC method
4.2.2.1. Impregnation
4.2.2.2. Thermosetting
4.2.2.3. Carbonization
4.2.3. Characterization
4.3. Results and Discussion
4.3.1. Properties of PMP
4.3.2. Interaction of PMP and reinforcement
4.3.3. High pressure HP method
4.3.3.1. Pressure
4.3.3.2. Heating rate
4.3.3.3. Reinforcement loading
4.3.4. Low pressure ITC method
4.3.4.1. Microstructure
4.3.4.2. Density
4.3.4.3. Porosity
4.3.4.4. Mechanical properties
4.3.4.5. Fractography
4.3.4.6. Helium gas permeability
4.3.5. HP method improvement
4.3.5.1. Shift studies
4.3.5.1.1. Temperature shift
86
86
87
88
88
89
89
89
89
89
93
95
96
101
105
109
109
112
115
116
117
119
121
121
124
xxxv
4.3.5.1.2. Time shift
4.3.5.1. Pressure enhancement studies
4.4. Summary of the Chapter
References
126
127
130
131
Chapter 5: Bipolar Plate Fabrication and Performance Evaluation
5.1. Preamble
5.2. Experimental
5.2.1. Raw materials and their processing
5.2.2. Bipolar plate fabrication
5.2.3. Bipolar plate characterization
5.2.4. PEM fuel cell assembly and testing
5.3. Results and Discussion
5.4. Summary of the Chapter
References
133-146
135
135
135
136
137
137
137
145
146
Chapter 6: Preliminary Study on Next Generation Bipolar Plate System
6.1. Preamble
6.2. Experimental
6.2.1. Raw materials
6.2.2. Preparation of C/SiC composite
6.2.2.1. Chopping
6.2.2.2. Exfoliation
6.2.2.3. Ball milling
6.2.2.4. Drying
6.2.2.5. Moulding of charge
6.2.2.6. Sintering of the green compact
147-159
149
150
150
150
151
151
151
151
152
152
xxxvi
6.2.3. Characterization of C/SiC composite
6.2.3 Fabrication of C/SiC composite bipolar plate
6.2.4. System level testing of C/SiC composite bipolar plate
6.4. Results and Discussion
6.5. Summary of the Chapter
References
152
152
153
153
159
159
Chapter 7: Conclusions and Future Scope
7.1. Conclusions
7.2. Future Scope
161-167
163
166
Research Output 169
Author Biodata 171
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