potential materials for fuel cells sri harsha kolli a …...potential materials for fuel cells by...

Potential Materials for Fuel Cells

By

Sri Harsha Kolli

A Thesis Presented in Partial Fulfillment

Of the Requirements for the Degree

Master of Science in Technology

Approved November 2014 by the

Graduate Supervisory Committee:

Arunachalanadar Madakannan, Chair

Changho Nam

Xihong Peng

ARIZONA STATE UNIVERSITY

December 2014

i

ABSTRACT

Proton exchange membrane fuel cells have attracted immense research activities from the

inception of the technology due to its high stability and performance capabilities. The major

obstacle from commercialization is the cost of the catalyst material in manufacturing the fuel

cell. In the present study, the major focus in PEMFCs has been in reduction of the cost of the

catalyst material using graphene, thin film coated and Organometallic Molecular catalysts. The

present research is focused on improving the durability and active surface area of the catalyst

materials with low platinum loading using nanomaterials to reduce the effective cost of the fuel

cells. Performance, Electrochemical impedance spectroscopy, oxygen reduction and surface

morphology studies were performed on each manufactured material.

Alkaline fuel cells with anion exchange membrane get immense attention due to very attractive

opportunity of using non-noble metal catalyst materials. In the present study, cathodes with

various organometallic cathode materials were prepared and investigated for alkaline

membrane fuel cells for oxygen reduction and performance studies. Co and Fe Phthalocyanine

catalyst materials were deposited on multi-walled carbon nanotubes (MWCNTs) support

materials. Membrane Electrode Assemblies (MEAs) were fabricated using Tokuyama

Membrane (#A901) with cathodes containing Co and Fe Phthalocyanine/MWCNTs and Pt/C

anodes. Fuel cell performance of the MEAs was examined.

ii

DEDICATION

To my parents Jyothi and Ravi Kumar Kolli &

To all the researchers working towards clean energy and sustainable world for a better

tomorrow.

iii

ACKNOWLEDGEMENTS

Firstly, I want to express my biggest accolade to my Chair, Guru and Mentor Dr.

Arunachalanadar Madakannan. His guidance, knowledge and support has driven me all through

my work in the laboratory and pushed me to learn more outside it by allowing me to get a very

wide range exposure in Fuel cells, Batteries, Off-Grid Solar Hybrid Systems, metal corrosion

and even Brownian motion which is very tough to find. I feel lucky to have a chance to work

under such innovative professor. I thank him for patiently guiding me throughout my work,

career and giving me an insight of the life ahead.

I am very thankful to my committee members Dr. Chango Nam and Dr. Xihong Peng for

guiding me throughout my thesis work and keeping track of the time.

I would like to thank my research advisors and friends Anthony Adame, Rashida Vilacorta

and Remya Raju for their invaluable support in starting my research and guiding the way

through obstacles faced through their valuable experience.

I would like to take this opportunity to thank my brother Rajesh Kolli who was my main

motivation to work in the field of research. His help from his valuable experience has driven

me to work harder all along.

I would like to thank the guidance offered by my colleagues and friends Prashant Ganeshram

and Ximo Chu for guiding me through the Batteries part of my research.

I am grateful for the guidance offered by the Post Docs in our lab Vignarooban and Xinhai

for guiding me through the chemical concepts.

I am very thankful to my colleagues Abinaya and Mathan Kumar for helping finish up things

in the laboratory.

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Lastly, I want to thank my friends for supporting me all through my life here at Arizona State

University and people working on clean energy who gave me motivation to work harder

towards a cleaner planet.

I would like to acknowledge the support provided by US Department of Energy (DOE) and

The utility company Salt River Project (SRP) for their financial support throughout my time

here at ASU Fuel Cell Laboratory.

v

TABLE OF CONTENTS

Page

LIST OF TABLES viii

LIST OF FUGURES ix

CHAPTER

1 INTRODUCTION.........................................................................................................1

1.1 Background..............................................................................................................1

1.2 Statement of Problem...............................................................................................4

1.3 Scope........................................................................................................................4

1.4 Objective..................................................................................................................4

2 LITERATURE REVIEW...............................................................................................5

2.1 History of Fuel Cells................................................................................................5

2.1.1 Alkaline Membrane Fuel Cells..........................................................................5

2.2 Major Hurdles and Losses in Fuel Cells..................................................................6

2.3 Nanomaterials for Catalyst Improvements...............................................................8

2.3.1 Carbon Nanotubes..............................................................................................8

2.3.2 Graphene..........................................................................................................10

2.3.3 Thin Film Catalysts..........................................................................................10

2.4 Oxygen Reduction on Carbon Supported Organometallic Phthalocyanines..........11

2.5 Electrochemical Impedance Spectroscopy.............................................................13

3 METHODOLOGY.......................................................................................................14

3.1 Pt/Graphene Synthesis............................................................................................14

3.1.1 Materials Used for Graphene Oxide (GO).......................................................14

3.1.2 Graphene Oxide Synthesis by Hummers Method............................................14

3.1.3 Preparation of Graphene from GO by Thermal shock.....................................16

3.1.4 Preparation of Graphene from GO in Inert Atmosphere..................................16

vi

CHAPTER Page

3.1.5 Carboxylic Functionalization of Graphene......................................................16

3.1.6 Preparation of Pt/Graphene using Two-Phase Transfer and ...........................17

Sodium Formate Reduction Method

3.1.7 Preparation of Pt/Graphene Using Two-Phase Transfer and...........................19

Sodium Borohydrate Reduction Method

3.2 Iron and Cobalt Phthalocyanine on MWCNTs......................................................21

3.2.1 Materials...........................................................................................................21

3.2.2 Synthesis...........................................................................................................21

3.3 Membrane Electrode Assembly Preparation..........................................................21

3.3.1 Pt/Graphene MEA Preparation.........................................................................21

3.3.1.1 Preparation of Catalyst Ink for Pt/Graphene Performance Testing......21

3.3.1.2 Membrane Preparation for Pt/Graphene Catalyst................................22

3.3.1.3 MEA Assembly....................................................................................22

3.3.2 MEA preparation for Organometallic Catalysts...............................................23

3.3.2.1 Membrane Electrode Assembly Preparation for Organometallic........23

molecular catalysts (Nickel-Phenyl-Benzene complexes)

3.3.2.2 Membrane Electrode Assembly Preparation for Evaluation of............23

Tokuyama A901 Alkaline Membrane

3.3.3 Pt Commercial Catalyst with 5 nm Co Thin Film Catalyst Preparation..........24

3.4 Electrochemical Impedance Spectroscopy.............................................................25

3.5 Fuel cell Test Procedure.........................................................................................26

3.6 Cell Activation Procedure......................................................................................27

3.7 Four Point Probe membrane Test Methodology....................................................28

3.7.1 Assembling Membrane test cell.......................................................................28

3.7.2 Test Procedure..................................................................................................30

3.8 Battery Testing Procedure......................................................................................31

3.9 Solar Thermal Metal Corrosion Testing Procedure...............................................36

vii

CHAPTER Page

4 RESULTS AND DISCUSIION...................................................................................37

4.1 Test results of Graphene Decorated with Pt nanoparticles.....................................37

4.1.1 Test results of Pt/graphene Reduced with HCOONa.......................................37

4.1.1.1 Polarization Results of Pt/graphene Reduced with HCOONa.............37

4.1.1.2 Electrochemical Impedance Spectroscopy Results and Comparison...43

4.1.2 Results of Pt/graphene Reduced with NaBH4.................................................45

4.1.2.1 Polarization Results of Pt/graphene Reduced with NaBH4.................45

4.1.2.2 Electrochemical Impedance Spectroscopy Results and Comparison...51

4.1.3 Results Discussion and Future Work...............................................................53

4.2 Tokuyama A901 Membrane Performance Results................................................53

4.2.1 Tokuyama A901 AMFC Membrane Performance with Pt/C Catalyst.............53

4.2.2 Tokuyama A901 Membrane Performance Results with..................................54

Iron and Cobalt Pthalocyanine

4.3 Polarization Results of Low Loaded Commercial Catalyst...................................55

with 5nm Cobalt Thin Film Cathode

4.4 Polarization of Organometallic Molecular (Ni, Ph, Bz) Complexes......................56

4.5 PVC and PVA Membrane Testing Results............................................................63

4.6 Battery Testing Results..........................................................................................65

4.7 Solar Thermal Metal Corrosion Testing Results....................................................69

5 CONCLUSION and DISCUSSION.............................................................................73

5.1 Overview................................................................................................................73

5.2 Future Work...........................................................................................................74

REFERENCES.........................................................................................................................76

viii

LIST OF TABLES

TABLE Page

1. Polarization Results at All Temperatures of Graphene/Pt with HCOONa Reduction……37

2. EIS Results at All Temperatures of Graphene/Pt with HCOONa Reduction……………..39

3. Polarization Peak Power Results at All Temperatures of……………………….………...45

Graphene/Pt with NaBH4 Reduction

4. EIS Results at All temperatures of Graphene/Pt with NaBH4 Reduction………………..47

5. Organometallic Molecular Catalyst Sample 2 Polarization 2 Peak Power Values.............60

6. Organometallic Molecular Catalyst Sample 3 Polarization 2 Peak Power Values……….62

7. PVC Membrane In-Plane Conductivity Results………………………………………….65

8. PVA Membrane In-Plane Conductivity Results………………………………………….65

ix

LIST OF FIGURES

FIGURE Page

1. PEMFC Schematic Diagram [1]……………………………………………………….....1

2. AMFC Schematic Diagram…………………………………………………………….....2

3. Low Temperature Fuel Cell MEA Cost Breakdown……………………………………...3

4. Losses in Fuel Cells [11]………………………………………………………………...11

5. GO synthesis process by hummer’s method……………………………………………..15

6. Graphene Functionalization………………………………………………………...........16

7. Decorating Pt Nanoparticles on Graphene Using HCOONa Reduction............................18

8. Decorating Pt Nanoparticles on Graphene Using NaBH4 Reduction................................20

9. Lesker Supersystem RF DC Sputter Coater.......................................................................24

10. Copper Mask for Sputtering..............................................................................................25

11. Sample Before and After Sputtering.................................................................................25

12. Typical Impedance Plot for Fuel Cell...............................................................................26

13. Fuel Cell Test Station with Integrated Test Cell...............................................................27

14. Membrane Placement in the Test Cell [89].......................................................................28

15. in-Plane Conductivity Test Cell........................................................................................29

16. Assembled Cell Inside a Fuel Cell Test Cell....................................................................30

17. SLA New Battery Test Schedule......................................................................................33

18. Schedule File Formula…………………………………………………….…………….34

19. ARBIN TEST SETUP…………………………………………………………………..35

20. CBA Test Setup…………………………………………………………………………36

21. Pt/Graphene (HCOONa Red.) Cell Performance at 40oC................................................38





x

FIGURE Page

26. Graphene/Pt with HCOONa Reduction: Polarization....................................................43

27. Impedance Plot at All Temperatures..............................................................................44

28. Impedance and Maximum Power Plots vs Temperature................................................45

29. Pt/Graphene (NaBH4 Red.) Cell Performance at 40oC..................................................46




33. Pt/Graphene (NaBH4 Red.) Cell Performance at 80oC................................................. 50

34. Pt/Graphene (NaBH4 Red.) Cell Performance at All Temperatures..............................51

35. Impedance Plot at All Temperatures...............................................................................52

36. Impedance and Maximum Power Plots vs Temperature.................................................53

37. A901 AMFC Polarization with Pt/C Catalyst.................................................................54

38. CO Sputtered Sample Polarization Curves.....................................................................56

39. Organometallic Molecular Catalyst Sample 1 Polarization……………………………58

40. Organometallic Molecular Catalyst Sample 2 Polarization 1………………………….59

41. Organometallic Molecular Catalyst Sample 2 Polarization 2………...………………..60

42. Organometallic Molecular Catalyst Sample 3 Polarization 1………...……………….61

43. Organometallic Molecular Catalyst Sample 3 Polarization 2………...……………….62

44. Organometallic Molecular Catalyst Sample 4 Polarization……………...……………63

45. Nafion 212 Membrane Test Results at 30oC………………………………...…………64

46. Charge and Discharge Capacities of SLA 100AH New Battery at C/5 rate (Auto.)..…66

47. Impedance Values of SLA 100AH New Battery at C/5 rate (Auto.)……………..……67

48. Discharge Capacities of SLA 100AH Old Battery………………………………..……68

49. Impedance Values of SLA 100AH OLD Battery…………………………………..…..69

xi

FIGURE Page

50. Corrosion Weight Loss of C276 at 800oC (Nacl+KCl)..………………………………70

51. Corrosion Weight Loss of SS-304 at 800oC (Nacl+KCl)….…………………………..71

52. Corrosion Weight Loss of C-276 at 900oC (Nacl+KCl+ZnCl2)…….…………………72

1

CHAPTER 1

INTRODUCTION

1.1 Background

Climate change and global warming are taking a front note in the present day problems that

can lead to the loss of human inhabitations. If the present trend continues it may be one of the

causes for human extinction. It is a critical time to do something to overcome this problems.

There are a lot of clean, renewable and alternative technologies to the present day fossil fuel

technologies such as solar energy, wind energy, hydrogen (fuel cells), geothermal, tidal. They

were not given consistent importance over a long period of time due to monopoly of the oil

industry in the production of energy until lately.

Fuel cell technology and battery technology have been considered as the key technologies that

can replace the fossil fuel technology in the automotive sector. Fuel cells are taken up as the

major future technology by most of the renowned automotive manufacturers throughout the

world due to its high power density and fast refuelling capabilities.

There are different fuel cell technologies for different kind of applications such as Solid oxide

fuel cells (SOFC), Phosphoric Acid (PAFC) and Molten carbonate fuel cells (MCFC) for

stationary and high temperature applications. Alkaline and alkaline membrane fuel cells (AFC

& AMFC) for deep space and automotive applications. Proton exchange membrane (PEM) fuel

cells for low temperature automotive and portable power applications as well as high

temperature applications.

In this thesis the major focus is on PEMFC and AMFC. The schematic and general reactions

that occur are as shown:

2

1 PEMFC Schematic Diagram [1]

General reaction mechanism for PEMFC

Anode Reactions: H2 2H+ + 2e−

Cathode Reactions: 2H+ + 2e− + O2 H2O

Overall Reactions: H2 + ½ O2 H2O

2 AMFC Schematic Diagram [2]

3

General reaction mechanism for AMFC

Anode reactions: 2H2+4OH− 4H2O+4e−

Cathode Reactions: O2+2H2O+4e− 4OH−

Total Reaction: H2 + ½ O2 H2O

1.2 Statement of Problem

PEM fuel cells for low temperature applications have the catalyst mainly composed of platinum

for the oxygen reduction reaction. This increases the effective cost of the fuel cell and is the

major hurdle for the Commercialization of the fuel cell apart from hydrogen production. The

catalyst cost plays a major factor in the $/KW value of the fuel cell technology as discussed

below

3 Low Temperature Fuel Cell MEA Cost Breakdown

The cost of catalyst sums to 53 % of the total MEA cost according to International Partnership

for Hydrogen and Fuel Cells in the Economy (IPHE) report [3], so it’s very important to reduce

Membrane, 10 %

Catalyst, 53.33%

GDL, 13.3%

Bipolar Plate, 16.66%

Balance of Stack, 6.66%

MEA COST BREAKDOWN

Membrane Catalyst GDL Bipolar Plate Balance of Stack

4

the cost of the catalyst used. As platinum is the main reason for the cost of the catalyst it’s of

utmost importance to reduce the amount of platinum used in the catalyst material.

1.3 Scope

The focus of this thesis is to study various alternative materials for catalyst supports and

catalysts to reduce the cost by increasing the surface activity, durability and decreasing the

platinum loading. The experimentation is designed as follows:

1. Synthesis of graphene from graphene oxide using hummer’s method

2. Pt decoration on graphene and MEA evaluation

3. Testing of tokuyama A901 Anion exchange membrane using Commercial and

organometallic catalysts

4. Evaluation of organometallic molecular catalysts for Proton Exchange Membrane fuel cells

5. Studying the effect of CO thin film on reduced platinum loaded catalyst

6. Battery cycling and effects of various discharge rates

7. Corrosion studies of C236 and SS304 alloy at 800oC for determining the corrosion rate for

solar thermal applications

1.4 Objectives

The main objective of my thesis is to find the materials needed to be researched for fuel cell

cost reduction and performance improvement. To optimize and find better synthesis

techniques for high performing graphene based Pt catalysts with better durability.

5

CHAPTER 2

LITERATURE REVIEW

2.1 History of Fuel Cells

Fuel cells were invented long back in 1839 by a lawyer scientist William Grove by inverting

the water electrolysis reaction using platinum metal electrodes as anode and cathode. From

then on they have come a long way but are yet to be fully commercialized [4]. PEMFC was

developed by Thomas Grubb in 1960s when working on a NASA project to manufacture fuel

cells for space applications while working for the General Electric Company ® [4]. There was

never a time when PEMFCs were very extensively used but the trend looks to change lately

with all major automotive companies adopting this technology for future vehicles. The only

barrier to commercialization is the cost and the hydrogen fuel supply chain.

2.1.1 Alkaline Membrane Fuel Cells

The Alkaline Fuel Cell (AFC) is an electrochemical device that converts the chemical energy

of H2 directly into electrical energy. The direction of reaction is reverse of alkaline water

electrolysis. In general the AFCs use a liquid electrolyte solution of Potassium Hydroxide

(KOH) because of its high conductivity among all the alkaline mediums. In the kinetics of

alkaline fuel cells the electrons are transferred to an external circuit load to the cathode where

the oxygen reacts with water to generate hydroxyl ions with are transferred through the medium

(electrolyte) to the anode where it reacts with hydrogen and generates water.

AFCs offer some advantages over other kind of fuel cells such as ease of handling ease of

handling because of their low operating temperatures (approximately 25-70 o C) and higher

reaction kinetics than the acidic media fuel cells such as PEMFC resulting in higher cell

voltages. The high conductive efficiency permits the usage of non-platinum materials

effectively decreasing the manufacturing cost of the fuel cell.

6

The main backdrop of AFCs is the KOH electrolyte solution is very sensitive in the presence

of CO2. When the AFC is exposed to air or CO2 atmospheric conditions the KOH reacts with

the CO2 forming potassium carbonate which decreases the effective weight and conductivity

of the KOH medium[5][6]. It’s due to this property that AFCs were not seen as a viable fuel

cell technology for terrestrial applications but has been extensively used for extra-terrestrial

applications application by various space organizations including NASA.

The concept of alkaline membrane fuel cells (AMFCs) came from the backdrop of liquid

electrolyte AFCs. When the medium can be converted into a solid state electrolytic membrane

the oxidation of KOH can be highly reduced and the mechanical stability can be incorporated.

This element has been a major focus of many researchers since the issue was discussed [7]

leading to the creation of anion conducting polymer electrolyte membranes. [8-10]

2.2 Major Hurdles and Losses in Fuel Cells

The major hurdles for fuel cells as discussed in the previous chapter is the cost of the fuel cells.

The major component of this hurdle is the cost of the catalyst which is directly associated with

the platinum. Another main problem that’s stopping fuel cells from being effectively is the

Hydrogen availability. Presently the hydrogen is being produce mainly from natural gas or

other fossil fuels. Even though the carbon imprint is less in generating hydrogen, it’s not

effective to the need of creating zero emission vehicles (ZEV). Presently there is a lot of

progress in generating hydrogen from solar with the help of cheap photoelctrochemical cells

(PEC) which electrochemically generate hydrogen from sunlight.

But apart from these there are a lot of losses in fuel cells which needs to be given importance

in the field of research to improve the efficiency and lifetime of the fuel cells for effectively

replacing IC engines. The losses can be separated as discussed in the polarization plot below.

7

4 Losses in Fuel Cells [11]

As represented in the plot we can see that there are a lot of losses associated with the fuel

cells like any other device according to the law of nature.

The losses in the plots can be split as follows:

Activation Losses: These losses take place due to slow kinetics on the catalyst before the

reactions take place.

Ohmic losses: These are the losses associated with the resistance to ion flow through the

electrolytes and through the electrodes.

Mass transport and concentration losses: These losses occur due to slow removal of product

and effective availability of the reactants on the surface of the catalyst.

8

So when considering to model a fuel cell all these constrains should be given the key

considerations.

2.3 Nanomaterials for Catalysts Improvement

2.3.1 Carbon Nanotubes

Carbon nanotubes are long cylinders of 3-cordinate Graphene layers of carbon, slightly

pyiramidalized by curvature from sp2 hybridization of graphene to diamond like sp3

hybridization [12, 13]. Carbon nanotubes were discovered in 1991 by Iijima as a minor by

product during fullerene synthesis [14]. Since then an effective remarkable progress has been

made in the carbon nanotube research including the discovery of three kinds of carbon

nanotube structural materials (single walled, double walled and multi walled carbon

nanotubes). Out of these multiwalled carbon nanotubes have been frequently used in research

and practical applications due to its ease of production and durability characteristics. Carbon

nanotubes have a very unique and peculiar characteristics in structural crystallographic,

mechanical, electronic and chemical properties. They exhibit exceptional strength, high

stiffness with high electrical and thermal conductivity. In the structural crystallography they

exhibit closed topology and tubular structure when compared to other forms of carbon[15-17].

Various great studies have been done for the steps taken during their synthesis, purification and

explanation of fundamental physical and chemical properties. In these investigative studies

major work has been done in studying the electrochemical properties of carbon nanotube

materials including the property of electrocatalysis of oxygen reduction in acidic [18-21] and

alkaline media [22-28].

Ajayans group reported some of the reasons for improved electrocatalysis for ORR due to

heptagon-heptagon defect pairs in lattice pentagons at the tips and curvature of CNT [15].

9

Different carbon-oxygen functionalities on the surface of CNTs are related to the

electrocatalytic activity for ORR in alkaline media. Matsubara and waki demonstrated that the

onset potential for the oxygen reduction on oxidised MWCNTs shifts positively by

approximately 60 mV compared with untreated MWCNTs [29]. This positive shift

demonstrates the possibility of oxygen functionalities introduced have a considerable effect on

the ORR capabilities of MWCNTs.

It has been proposed in many cases the catalyst impurities remaining in the CNTs during the

fabrication by chemical vapour deposition (CVD) process are responsible for the

electrocatalytic activity of MWCNTs in various reactions. The role of metal impurities in ORR

has been discussed [18]. Even acid washing of prepared CNTs doesn’t completely get rid of

the iron impurities that exist in CNTs [30]. This remains the fundamental challenge of the

carbon nanotube science to develop simple cost effective purification techniques instead of the

harsh purification techniques to remove amorphous carbon and metal impurities (usually Fe,

Co, Mo or Ni) used in their growth [31-36].

The purification of CNTs is most effective with the mixtures of HNO3 and H2SO4 for removing

amorphous carbon and HCL treatment is considered as the best purification method for

removing metallic impurities from CVD synthesized CNTs [37]. During this process of

purification it introduces oxygenated functional groups on ends and side holes of CNTs.

Although the exact electrocatalytic role of the surface functional groups is not clearly known

the acid treatment is important from catalyst point of view because of its ability to support

active electrocatalytical materials onto their surface [38].

10

2.3.2 Graphene

Graphene is a monolayer of carbon mainly derived from graphite and looks like fullerene from

which it gets its name. Graphene was invented by Andre and Kostya in 2004 using a simple

surface science method by peeling of layers of graphite with extensive care to form thin films

of carbon. [39] Its referred to as the wonder material in the scientific world due its applicability

in multiple fields mainly due to its very high conductive property, high surface area and its 2-

D structure. Due to these wondrous properties the scientists were awarded a noble prize for the

invention in the year 2010[40]. Even though the scientific pair made the inventions, the patent

for graphene was already accepted by US Patent office by that time [41].

From then on various methods of extracting graphene were created using chemical,

electrochemical and thermal processing but the major focus was on creating the graphene from

graphene oxide. In all these methods Hummers method [42] is widely used in the

manufacturing of graphitic oxide or graphene oxide. Lu Wang and team tested the best

chemical methods for preparation of graphene for electrochemical purposes and came to a

conclusion that Hummers method can produce the highest activity in all [43]. This is why

hummer’s method was chosen over all other methods in this research work.

2.3.3 Thin Film Catalysts

Wilson and Gottesfeld of Los Almos National Laboratory firstly published the use of thin film

catalsysts for PEM fuel cells in 1992[44]. Their research showed that coating of catalysts with

thin films of Pt increases the lifetime and decreases the degradation of the catalytical material

of a fuel cell in acidic media.

Similar research was done by Zhe Tang and group but with a Co deposition instead of Pt and

got better performance and less catalyst degradation after cycling for a Nafion 115 membrane.

11

Their main focus was also to determine the best thickness of the Co thin film islands on the

catalysts and it was found that 5nm thick Co layer produces the best output of all. The output

of the catalyst with thin film was higher than the output for the catalyst of same loading without

the thin film.[45]

2.4 Oxygen Reduction on Carbon Supported Organometallic Phthalocyanines

When oxygen reacts on the cathode, it’s very crucial to reduce it by four electron pathway

rather than a two electron pathway. But in reality most of the catalytical materials promote to

two electron pathway where the intermediate product is H2O2 which is produced due to high

dissociative energy of the O-O bond. Platinum catalysts for fuel cells mainly employ 4 electron

pathway for oxygen reduction in both alkaline and acidic conditions [46] but the cost

limitations of platinum has led the researchers to produce alternative materials to platinum for

catalysis in fuel cells[47]. Since then several articles have focused on MN4 macrocyclic

compounds have been published [46, 48-51].

The ability of oxygen reduction of MN4 macrocycles has led to an enormous research on these

materials in alkaline and acidic media. [52-66]. Various researches have shown that the

mechanism of ORR depends on the nature of metal at the center of these complex organic

molecules. For Iron Phthalocyanine it has been found that at low over potentials a four electron

reduction is possible where many other complexes containing Ni,Co and Cu have shown

oxygen reduction via two electron pathways. But similar electro catalytic activities have been

reported for cobalt Phthalocyanine and it has also shown the ability to promote four electron

pathways of oxygen reduction to water without formation of a peroxide intermediate [67].

The catalytic activity of the MN4 macrocycles is often related to the redox potentials of the

metals M (III)(II) complexes . The more positive the redox potential of the elctrocatalyst

12

couple, the higher the catalytic activity of the macrocyclic complexes. The interactions between

the O2 molecule and the central atom premise the breaking of the O-O bond. The metal should

always be in M(II) state to promote this reaction. If the metal is in M (III) state it has to be

reduced to M(II) state.

In alkaline media the following reactions take place [68]:

M (III)-OH + e_ M (II) + OH-

M (II) + O2- M (III)-O2- or M (III)-O2

Which undergo as follows:

M (III)-O2 + e- M (II) + Intermediates

It is also worth mentioning the role of support materials as they can also act as axial ligand,

therefore the properties of the complexes in adsorbed states can be different [68]. Out of major

carbon materials functionalizing carbon nanotubes with FePc and CoPc were reported to

improve the catalytic properties of the complexes [69-71]. Phthalocyanines absorb effectively

onto the CNTs via non covalent π-π interactions and form molecular Phthalocyanine electrodes

[50, 51].

The long term stability of the micro cyclic catalysts is a major factor for electrocatalysis. The

formation of hydroxyl radicles form a radicle role in the degradation MN4 micro cyclic catalyst

materials [72]. It has been found that pyrolysis of the MN4 materials can improve the

electrocatalytic activity and enhance the stability of the catalyst very effectively. Numerous

research activities have been reported in finding the optimized conditions for pyrolysis of these

complexes [73-76]. The temperatures used for pyrolysis in inert atmosphere vary from 500-

1000o C but highest activity has been reported when the pyrolysis temperatures range between

13

500o to 600oC. At higher temperatures the activity of the catalyst can decrease but the stability

can be improved. The exact process and the chemical transitions occurring during pyrolysis is

still not known and is under debate [77] [78].

2.5 Electrochemical Impedance Spectroscopy

The frequency vs. impedance evaluation technique using nyquist and bode plots to determine

the impedance of the fuel cell. It uses the complex electronic elements of the PARSTAT to

determine the impedance of the cell at any given frequency [79]. For this study the high

frequency response (HFR) is the main impedance used to determine the actual IR and complete

Polarization losses in the fuel cell.

14

CHAPTER 3

METHODOLOGY

3.1 Pt/Graphene Synthesis

3.1.1 Materials Used for Graphene Oxide (GO)

Graphite (99.99 % pure) powder was procured from Superior Graphite, Illinois. Sodium

Nitrate, Potassium Permanganate and Hydrogen Peroxide were purchased from Carolina

Biology Supply Co (Burlington, North Carolina). NMP was purchased from Fischer Scientific

(Hampton, New Hampshire).

3.1.2 Graphene Oxide Synthesis by Hummers Method [42]

2 grams of graphite is added to 46 ml of concentrated sulphuric acid in an ice bath and stirred

for 15 minutes. 1 g of NaNO3 is added to the mixture under constant stirring. After 15 minutes

6g of KMnO4 is added very slowly to the mixture for a period of 30 minutes. The solution is

then taken out of the ice bath and the mixture is kept on stirring for 1 h till it reaches room

temperature. 92 ml of DI water at RT is added very cautiously to the mixture and stirred for 15

minutes. 280 ml of warm DI water (around 30oC) is added to the mixture and stirred for a while.

Finally 10 ml of 30% H2O2 solution is added to the mixture till the mixture turns into bright

yellow colour.

The resultant solution is separated into two parts and 1000ml of DI water is added to the

solution. The DI water above the sediment is removed the next day and the process is repeated

until the PH value reaches 5. The residue is then centrifuged until the PH value reaches to 7.

The residue is then dried in a vacuum oven at 60oC for 48 hours to get dry Graphene oxide.

The process flow chart is as follows

15

6 g KMnO4 added slowly

for 30 Min & Remove beaker

from Ice Bath

Add 92 ml DI Water

(Temp. reaches 98oC)

Add 280 ml of warm DI water

ADD 10 ml of 30% H2O2 till the

mixture turns yellow

46 ml Conc. H2SO4 + 2 g

Graphite (99%) +1g NaNO3 in

a Beaker inside an ICE BATH

Split the content into two 1L

Beakers and fill DI water

Continue until PH=5

Centrifuge the samples at 5000

RPM

Until PH = 7

Dry the sample in a Vacuum

oven at 60oC for 48 H

30 Min Stirring

1 Hour Stirring

30 Min Stirring

15 Min Stirring

5 GO synthesis process by Hummers method

16

3.1.3 Preparation of Graphene from GO by Thermal shock

Thermoscientific tubular furnace is pre heated to 1050oC and then 400mg of GO in an alumina

crucible (exposed to inert gas before heating) is heated in the oven for 30 seconds till the

popping sound stops. The crucible is then removed from the furnace and cooled to room

temperature. The material left in the crucible is graphene. [80]

3.1.4 Preparation of Graphene from GO in Inert Atmosphere

200 mg of GO is taken in an alumina crucible and inserted into the tubular furnace at room

temperature. Argon gas is let flow through the furnace until most of the atmosphere in the

furnace is turned inert. The sample is then heated to 450oC for 30 minutes and turned off in

inert atmosphere and the furnace is cooled down to room temperature before extracting the

sample from the furnace. The resultant sample in the crucible is graphene and is weighed to be

close to 100mg. [81]

3.1.5 Carboxylic Functionalization of Graphene

275mg of citric acid is mixed with 1.5ml of DI water. 100mg of graphene is added to the

solution and the mixture is ultrasonicated for 15 minutes followed up by vigorous stirring for

1 hour. The mixture is then filtered and heat treated in an air furnace at 300oC for 30 minutes

to get carboxylic functionalized graphene. [82]

100 mg Non-

Functionalized

Graphene is mixed

with 225 mg citric

acid in 1.5 ml DI

water

The sample

is stirred for

1 Hour

The sample

is filtered

and heat

treated at

300oC for 30

minutes

Func.

Graphene

6 Graphene Functionalization

17

3.1.6 Preparation of Pt/Graphene Using Two-Phase Transfer and Sodium Formate

Reduction Method

0.025 ml of H2PtCl6.6H2O is added to 1.5 ml of DI water to make a solution of 0.083 M

chloroplatinic acid solution. 223 mg of Tetra octyl ammonium bromide (ToAB) is added to

2ml of toluene to make 0.18M solution. Both the solutions are mixed and are subjected to

vigorous stirring until the phase transfer takes place. The orange colour part of the mixture is

extracted and taken into a separate vile. 100mg of functionalized graphene is slowly added to

the extracted mixture and vigorously stirred for one hour. 0.35 ml of 1-Dodecanethiol is added

to dropwise to the solution for 30 mins under constant stirring. 340 mg of sodium formate in 5

ml of DI water is added to the mixture slowly for 2 hrs at 60oC to reduce and evaporate the

residue organic compounds left in the solution. The resultant mixture is filtered out and dried

overnight in a vacuum oven at 100oC. The resultant Pt/Graphene is subjected to pyrolysis at

800oC in a tubular furnace with flowing argon atmosphere for 1 hour, this is mainly for

activating the platinum nanoparticles on graphene to have high surface activity [82]

18

Both solutions mixed

together under rigorous

stirring until a dark orange

organic layer is formed

over a clear solution

0.025 ml of

H2PtCl6.6H2O

in 1.5ml DI

water

243 mg

ToAB in

2ml Toulene

The orange organic

layer is extracted

into a separate vile

100mg of Functionalized

graphene is added to the

organic material

0.35 ml of DDT

is added slowly

for 30 Min

340 mg of HCOONa

in 5 ml DI water is

added dropwise at

60oC

The mixture is

filtered and Pt/

Graphene is

extracted

The sample is dried

over night in a

vacuum oven at

100oC and Then

heat treated in Ar

atmosphere at

800oC for 1 H

30 Min.

1 Hour

2 Hours

7 Decorating Pt nanoparticles on graphene using HCOONa Reduction

19

3.1.7 Preparation of Pt/Graphene Using Two-Phase Transfer and Sodium Borohydrate

Reduction Method

0.025 ml of H2PtCl6.6H2O is added to 1.5 ml of DI water to make a solution of 0.083 M

chloroplatinic acid solution. 223 mg of Tetra octyl ammonium bromide (ToAB) is added to

2ml of toluene to make 0.18M solution. Both the solutions are mixed and are subjected to

vigorous stirring until the phase transfer takes place. The orange colour part of the mixture is

extracted and taken into a separate vile. 100mg of functionalized graphene which is previously

dispersed in NMP, filtered and dried is slowly [83] added to the extracted mixture and

vigorously stirred for one hour. 0.35 ml of 1-Dodecanethiol is added to drop wise to the solution

for 30 mins under constant stirring. 5 ml of 0.5M sodium borohydrate (NaBH4) in 1M NaOH

[83] is added to the mixture drop wise for 2 hrs. at 60oC to reduce and evaporate the residue

organic compounds left in the solution. The resultant mixture is filtered out and dried overnight

in a vacuum oven at 100oC. The resultant Pt/Graphene is subjected to pyrolysis at 800oC in a

tubular furnace with flowing argon atmosphere for 1 hour, this is mainly for activating the

platinum nanoparticles on graphene to have high surface activity for fuel cell catalysis.

20

Both solutions mixed

together under rigorous

stirring until a dark orange

organic layer is formed

over a clear solution

0.025 ml of

H2PtCl6.6H2O

in 1.5ml DI

water

243 mg

ToAB in

2ml Toulene

The orange organic

layer is extracted

into a separate vile

100mg of Functionalized

graphene is added to the

organic material

0.35 ml of DDT

is added slowly

for 30 Min

5 ml of 0.1M NaBH4

in 1M NaOH is

added dropwise at

60oC

The mixture is

filtered and Pt/

Graphene is

extracted

The sample is dried

over night in a

vacuum oven at

100oC and Then

heat treated in Ar

atmosphere at

800oC for 1 H

30 Min

1 Hour

2 Hrs

8 Decorating Pt nanoparticles on graphene using NaBH4 Reduction

21

3.2 Iron and Cobalt Phthalocyanine on MWCNTs:

3.2.1 Materials

The iron (II) phthalocyanine (FePc) and cobalt (II) phthalocyanine (CoPc) were purchased

from Sigma Aldrich. The multiwalled carbon nanotubes (MWCNTs, purity >95%, diameter 30

+10 nm, length 5-20 mm) used were purchased from Cheaptubes, Inc. (Cambridgeport, VT,

USA) and commercial 46.1 wt.% Pt catalyst supported on Ketjen Black was purchased from

Tanaka Kikinzoku Kogyo K.K. (Japan). Anion exchange membrane (model # A201 and

#A901) samples were provided by Tokuyama (Tokuyama Corporation, Tokyo 100-8983,

Japan). A 5 wt.% OH- ionomer solution (AS4,Tokuyama Corporation, Japan) was used in the

preparation of catalyst ink in water.

3.2.2 Synthesis

First to disperse the Iron and Cobalt Phthalocyanine onto the Multi-walled carbon

nanotube surface 200mg FePc or 200 mg Copc and 200 mg of MWCNTs are dispersed in

40ml isopropanol and sonicated for 30 min and this process is followed by stirring for 1h. The

solution is filtered using a G4 glass filter and the resulting homogeneous mass is placed in a

ceramic boat and vacuum dried at 100o C and then pyrolysed at 800oC for 2 h in a tubular

furnace with flowing argon atmosphere [84].

22

3.3 Membrane Electrode Assembly Preparation

3.3.1 Pt/Graphene MEA Preparation

3.3.1.1 Preparation of Catalyst Ink for Pt/Graphene Performance Testing

Anode: 200 mg of Platinum carbon commercial catalyst (Tanaka 40% Pt wt.) is subjected to

inert atmosphere in a round bottom flask for 30 minutes. 4 ml of Isopropyl alcohol is added to

the catalyst slowly and then 2 ml of 5 wt. % ionomer is added to the solution and the resultant

mixture is sonicated and stirred slowly for a period of 4-6 hours and ultrasonicated again to get

the ink. [85][86]

Cathode: 100 mg of Pt/Graphene is taken in a round bottom flask and subjected to inert

atmosphere for 30 minutes. 2 ml of isopropyl alcohol is added to the powder and then 1 ml of

5wt. % ionomer is added to the solution. The resultant solution is ultrasonicated and stirred

slowly at 60 RPM for 4-6 hours and ultrasonicated for 1 hour to get the ink [86].

3.3.1.2 Membrane Preparation for Pt/Graphene Catalyst

0.4 ml of catalyst ink is deposited on center of 6cm2 nafion membrane using micro spray

technique with an effective surface of 5 cm2 and effective Pt loading of 0.4 mg/cm2 which acts

as a cathode and sintered at 70oC in vacuum oven for 20 minutes. 0.2 ml of catalyst ink is

deposited on the other side of the membrane using micro spray technique to get an effective

loading of 0.2mg/cm2 on a 5cm2 surface and sintered at 70o C in vacuum oven for 10 minutes

before assembling it into the test cell.

23

3.3.1.3 MEA Assembly

The MEA was assembled by sandwiching the coated membrane inside the test cell

(Fuel Cell Technologies Inc, Albuquerque, NM, USA) with gas diffusion layers fabricated

in lab using the wire rod coating technique[87]. The gas sealing was achieved using a

silicone fabric gasket (Saint Gobain performance plastics, USA) and by using a uniform

torque of 45 psi for sealing the cell.[84]

3.3.2 MEA preparation for Organometallic Catalysts

3.3.2.1 Membrane Electrode Assembly Preparation for Organometallic Molecular

Catalysts (Nickel-Phenyl-Benzene complexes)

0.5 ml of catalyst ink is deposited on center of 6cm2 nafion membrane using micro spray

technique with an effective surface of 1 cm2 which acts as a cathode and sintered at 70oC in

vacuum oven for 20 minutes. 0.2 ml of catalyst ink is deposited on the other side of the

membrane using micro spray technique on a 1cm2 surface and sintered at 70o C in vacuum oven

for 10 minutes before assembling it into the test cell.


(Fuel Cell Technologies Inc, Albuquerque, NM, USA) with 0.23 mm carbon paper as the

gas diffusion layers. The gas sealing was achieved using a silicone fabric gasket (Saint

Gobain performance plastics, USA) and by using a uniform torque of 45 psi for sealing

the cell.[84]

24

3.3.2.2 Membrane Electrode Assembly Preparation for Evaluation of Tokuyama A901

Alkaline Membrane

Membrane electrode assemblies (MEAs) are fabricated with commercial carbon supported

Pt catalyst (Pt/C) as anode and Fe/MWCNT, CoPc/MWCNT, Pt/MWCNT, Pt/c on

cathode side of the tokuyama polymeric membrane (A201 and A901 membranes,

Tokuyama Corporation, Japan) .Catalyst ink is prepared by adding DI water to the

catalyst material(4ml for 200mg catalyst) and 5 wt.% ionomer(AS4 ionomer, Tokuyama

Corporation, Japan) dispersion(2ml for 200mg catalyst) is added to the slurry[85][86].

The catalyst ink is stirred at slow pace for 4-6 hours and ultrasonicated for 5 min

every hour. The ink thus prepared is sprayed onto the tokuyama polymeric membranes

by using a microspray technique with an active surface area of 5 cm2. The catalyst

loadings were 0.4 mgcm-2 and 0.6mgcm-2 on anode and cathode part respectively. The

thus prepared sample was sintered in a vaccum oven at 70oC for 15 mins per side.


(Fuel Cell Technologies Inc, Albuquerque, NM, USA) with gas diffusion layers fabricated

in lab using the wire rod coating technique[87]. The gas sealing was achieved using a

silicone fabric gasket (Saint Gobain performance plastics, USA) and by using a uniform

torque of 45 psi for sealing the cell.[84]

3.3.3 Pt Commercial Catalyst With 5 nm Co Thin Film Catalyst Preparation

The fuel cell membrane is prepared by coating the Nafion 212 membrane with 0.2mg/cm2

Platinum loading on each side with Tanaka commercial Pt catalyst. A copper mask is prepared

with 5cm2 opening in the center for the deposition of Cobalt thin film in Lesker Supersystem

II RF DC Sputtering machine. The sample is placed inside the sputtering machine sample

holder inside a bell jar. A Co metal target is placed in the target holder. A pressure of 10-10 torr

25

is maintained inside the chamber. The 5nm size of the deposition is controlled by an automated

system and the procedure is carried out for 15 min to get a 5 nm thin film islands on the

commercial Pt cathode layer. The pressure is released and the sample is carefully taken out.

The mask is removed and fuel cell is then assembled into the test cell for further testing.

9 Lesker Supersystem RF DC Sputter Coater

10 Copper Mask for Sputtering

26

Sputtering

Nafion 212 Membrane

Cathode

Anode

5 nm Co Thin Film

11 Sample Before and After Sputtering

3.4 Electrochemical Impedance Spectroscopy

The electrochemical impedance spectroscopy testing is carried out using PARSTAT 2273

electrochemical testing tool to determine the cell and polarization resistances. The impedance

curves (Nyquist plots) are swept typically from 250 kHz to 10 mHz to get a total impedance

curve of the present fuel cell testing. For the present experimentation the curves are swept at

various temperatures to check the change in polarization resistance with respect to the

maximum power generated. The typical Z plots and the determination of resistance is depicted

as as shown in the figure below.

Nafion 212 Membrane

Cathode

Anode

27

12 Typical impedance plot for fuel cell

3.5 Fuel Cell Test Procedure

The fuel cells are tested using a green light test station (Horizon Fuel Cell Technologies) which

is automated test station with all kinds of polarization testing capabilities. It has an internal

flow regulation and humidification system. Hydrogen, oxygen or argon are connected on the

anode and the cathode input to the test station. The fuel cell is assembled in a test cell and

connected to the system as shown below. The cell is heated to various temperature levels .The

performance of the fuel cell is studied at various flow rates and humidity levels to determine

the optimum operating and best performance condition for the fuel cell with different materials.

28

13 Fuel Cell Test Station with Integrated Test Cell

3.6 Cell Activation Procedure

The fuel cell is activated using cyclic voltammetry cycling between two potentials. This

procedure is followed to start the kinetics in the electrode and through the electrolyte. Each cell

is typically cycled from 0.1 to 1.1 V for 90 cycles to achieve the activated phase. The

experimentation is carried out by plugging in the running fuel cell on the test station to the

PARSTAT 2273 terminals. All the parameters are set in the Power Suite program and the test

is run without interruption.

29

3.7 Four Point Probe Membrane Test Methodology

The four point probe membrane testing was done according to the Department of Energy

principles using a procedure designed by BEKKTECH Corporation [88]. The step by step

procedure for performing the testing is as shown below:

3.7.1 Assembling Membrane Test Cell

1. The membrane is cut into 5mm x 25mm dimensions and rested on a flat surface overnight

to get a flat surface.

2. The thickness of the sample is then measured using a micrometer

3. The membrane is then placed inside the test cell as shown in the figure below

14 Membrane Placement in the Test Cell [88]

The membrane is placed below the Pt wires in the center and above the Pt mesh in the ends of

the test cell membrane holder.

4. The membrane holder top is then assembled back safely and then conductivity cell is

placed inside the fuel cell test cell (Fuel Cell Technologies, Albuquerque, New Mexico,

USA) as shown below.

30

15 In-plane Conductivity Test Cell

31

16 Assembled Cell Inside a Fuel Cell Test Cell

3.7.2 Test Procedure

The following step by step procedure is employed for testing the In-Plane membrane

conductivity.

1. Argon and hydrogen are given as the inputs to the fuel cell test station on the cathode and

anode side respectively.

2. The test cell is connected to the argon supply and the other two input output terminals are

blocked. The flow rate is set to 0.5 nlpm at 100% RH level and the cell is left for 1 hour.

3. The argon terminals are replaced with H2 terminals and gas is let flow at 1 nlpm at the

required temperature and 100% RH for 2hours before running the testing.

32

4. The I-V curves are swept using Power CV software using PARSTAT 2273 instrument with

terminal connections as shown in the figure above. The settings are set as follows:

Voltage: E1 = -0.3V, E2 = 0.3V

Scan Rate: 10mV/S

Step Rate: 10mV

5. The curves are plotted in a data analysis software and the slope of the plot is found which

gives the resistance value.

6. Conductivity is found out using the formula below:

𝐶𝑜𝑛𝑑𝑢𝑐𝑡𝑖𝑣𝑖𝑡𝑦 = 𝐿𝑒𝑛𝑔𝑡ℎ 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑑𝑒𝑠 (𝐿)

(𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒(𝑠𝑙𝑜𝑝𝑒)𝑋 𝑤𝑖𝑑𝑡ℎ 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒(𝑊) 𝑋 𝑇ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠(𝑇)) S/cm

7. The process is repeated for different temperatures to find conductivity at various

temperatures and to find out the best operating temperature and humidity levels.

3.6 Battery Testing Procedure

Batteries are tested under a testing protocol designed specially to test the grid level utility of

the batteries. In this case the batteries being tested are sealed Lead Acid Batteries which are

extensively used in the present day utility. The test protocols of various other technologies

are also studied for future purposes which are not included as part of this thesis.

The batteries are tested using an automated battery test station designed by ARBIN

Instruments ®, College Station, Texas. One of the battery is tested semi-manually using a

table top battery charger and CBA IV computerized battery analyser for discharge analysis.

33

The typical battery testing in the present case involves cycling the battery and testing the state

health of the battery by checking the impedance of the cell at the end of each test. The charge

and discharge capacities are also recorded for each cycle to calibrate the effect of impedance

on the capacity.

For the automated testing the following schedule file as shown is used in MITS Pro software.

17 SLA New Battery Test Schedule

Each charge and discharge step can be varied with various test conditions in the automated

system. A formula can also be written in the software to control the limits and conditions of

testing from time to time.

In the present schedule file as shown above a 100 AH battery with no charge is taken and first

fully charged. As it’s a 3-Cell lead acid battery, by considering the theoretical voltage of the

battery which is 2.2 V (Lead Acid Battery) the battery is first charged to 6.8 V at C/5 charge

rate of 20A. And then the battery is discharged and charged for 3 cycles as shown in the loop

34

tab above at C/5 rate of 20 A . The battery is charged to 103% of the battery discharge

capacity after every discharge cycle with the help of a formula written inside the software as

shown below.

18 Schedule File Formula

35

The test setup using automated test station is as shown below.

19 ARBIN TEST SETUP

For the Semi-Manual test the battery is charged at 15 A using a table top Die Hard charger

and discharged at 8 A using CBA IV battery analyzer as shown below.

36

20 CBA Test Setup

In both the cases the batteries are deep discharged to 3V to check the deep cycled battery life

of the batteries. The impedance of both batteries are tested using a PARSTAT 2273

electrochemical test machine at a charged state for various cycles with a frequency sweep

range of 10kHz to 10mHz with an amplitude of 160mV. The HFR response gives the actual

impedance of the cell to study the health of the battery.

37

3.7 Solar Thermal Metal Corrosion Testing Procedure

In this process we test the corrosion levels of different alloys at high temperatures in various

concentrations of cheap salt solutions. The step by step procedure is as discussed below.

1. The alloys need to tested are cut into small pieces of known area that can fit in the quartz

tubing.

2. Two samples are generally taken of each alloy to reduce the anomalies that can be present

during the testing.

3. The salt mixture is prepared with the required concentrations as suggested by the DOE.

4. The salt solution is then turned into molten state at the melting point in a cylindrical

furnace and before it hardens itself the homogenous salt mixture is then poured into the

quartz tubing containing the alloys need to be tested.

5. The vile is let to dry and is topped off in such a way that no air can be present inside the

vile that effects the reaction/corrosion of the alloy with the salt.

6. The tubing was sealed with a cap and high temperature cement so that no air can pass

through into the tube, thereby isolating the corrosion of the alloy from external influences

inside the furnace.

7. The setup is then placed inside the high temperature oven at desired test temperature and

the heating is continued for longer periods with a minimum of one month.

38

CHAPTER 4

RESULTS AND DISCUSSION

4.1 Test Results of Graphene Decorated With Pt Nanoparticles

4.1.1 Test Results of Pt/Graphene Reduced With HCOONa

4.1.1.1 Polarization Results of Pt/Graphene Reduced With HCOONa

The polarization response of the fuel cell is studied according the procedure explained in

section 3.5 of the previous chapter and activated according to the procedure described in section

3.6. For the present membrane with Pt/Graphene cathode the polarization test is carried out at

40, 50, 60, 70 and 80o C respectively with a flow rate of 0.2 and 0.3 nlpm of H2 & O2

respectively. The results at each temperature are discussed in the following content.

Temperature 40oC:

21 Pt/Graphene (HCOONa Red.) Cell Performance at 40oC

39

The output of the fuel cell was clean at 40oC but the rate of voltage drop with respect to

current was very high than its supposed to be for a regular commercial catalyst. The

maximum performance was recorded at 0.36 V and 447 mA/cm2 and was found to be 162.6

mWcm-2.

Temperature 50oC:


The output of the fuel cell while testing is as recorded in the graph above. The voltage drop

with respect to current was better than that of the performance at 40oC but still very low. The

maximum performance was achieved at 0.34 V a little lower than the maximum power

voltage at 40oC and the current density was achieved to be 546 mAcm-2 to get a power

density of 187.9 mWcm-2.

40

Temperature 60oC:


The fuel cell performance with varying current is recorded as shown in the figure above. The

voltage drop with current was comparatively less at this temperature, probably due to faster

kinetics than the lower temperatures. The fuel cell showed a maximum performance at 0.39 V

and 498 mAcm-2 and produced a maximum power output of 195.7 mWcm-2. But it can be

observed that there is a peculiar drop in current density and increase in the voltage at the peak

power condition when compared to lower temperatures.

41

Temperature 70oC:


The voltage drop with current is lower than the previous cycles at lower temperature. This

means that the kinetics have increased inside the cell due to higher surface activity. The peak

performance at 70oC is achieved at 0.34 V with a current of 597 mAcm-2 and with a

maximum power output of 205.5mWcm-2. This performance is consistent increase with

respect to lower temperature outputs of 40oC and 50oC apart from the peculiar voltage and

current values at 60oC which showed higher voltage and lower current levels.

42

Temperature 80oC:


The performance results of the cell at 80oC are as shown above. The voltage profile was

relatively the best as expected at high temperatures due to faster kinetics. The maximum

performance was achieved at a voltage of 0.37V but the current density remained the same as

that of 70oC at 597mAcm-2 with a peak power density of 220mWcm-2.

43

All temperatures performance:

26 Graphene/Pt with HCOONa reduction: Polarization

1 Polarization results at all temperatures of Graphene/Pt with HCOONa reduction

Temperature

Voltage(V)

Current

Density(mAcm-2)

Max. Power

Density(mWcm-2)

40oC 0.36 447 162.6

50oC 0.34 546 188

60oC 0.39 498 195.7

70oC 0.34 597 205.5

80oC 0.37 597 220

44

4.1.1.2 Electrochemical impedance spectroscopy results and comparison

All temperature EIS plots:

27 Impedance plot at all temperatures

The nyquist trend indicates that the impedance is decreasing consistently with temperature. The

values of polarization resistances and their relation to maximum power output at a temperature

are discussed below.

45

(41) (b)

28 Impedance and Maximum Power Plots vs Temperature: (a) Impedance vs Temperature;

(b) Maximum Power Density vs Temperature

Temperature (oC) Polarization Impedance (m)

40 259.2

50 246.1

60 237.6

70 227.6

80 245.8

2 EIS Results at All Temperatures of Graphene/Pt With HCOONa Reduction

Form the plots it can be observed that the impedance is consistently decreasing with

temperature except for 80oC .The impedance increased peculiarly at 80oC though the

performance was the highest, this can be because of the concentration polarization due to the

ineffective removal of product from the cathode side. Or this can just be because of

disturbances in the measurement system of the PARSTAT.

46

4.1.2 Results of Pt/graphene Reduced With NaBH4

4.1.2.1 Polarization Results of Pt/Graphene Reduced With NaBH4

The MEAs are testing using the same methodology as discussed in the section 4.1.1.1. For

the current sample the testing was done at 40,50,60,70 and 80oC respectively. The flow rate

was set to 0.2 and 0.3 nlpm for Hydrogen and oxygen respectively. The performance with

temperature variation will be discussed in the following content.

Temperature 40oC:

29 Pt/Graphene (NaBH4 Red.) Cell Performance at 40oC

The performance results of the cell at 40oC are as shown in the figure. The best performance

was achieved at 0.36 V with a current density of 456 mAcm-2 and the peak power at this

point was found to be 165.8 mWcm-2.

47

Temperature 50oC:


The performance of the cell at 50oC is as shown above. The best performance was achieved

at 0.28V with a current density of 597.7 mAcm-2 and the peak power was found to be 167

mWcm-2. This value is not much higher than the previous temperature, this can be due to the

higher voltage drop levels in the cell as proved by the low voltage at the peak power

performance.

48

Temperature 60oC:


The performance at 60oC was achieved as shown above. The peak power of 218.9 mWcm-2 is

achieved at 0.34 V with a current density of 636 mAcm-2. There is a revival in the peak

power voltage level and the current density is following the increasing trend, this increased

the peak power to much higher value than the previous temperature.

49

Temperature 70oC:


The performance of the cell at 70oC was clean and without any fluctuations unlike the lower

temperatures. The maximum power density of 235.7 mWcm-2 was achieved at 0.36V with

current density of 648 mAcm-2. The current density increase was less but there was a little

voltage revival of the peak power voltage which increased the peak power value of the cell.

50

Temperature 80oC:


The cell behaved very peculiarly at 80oC, there was a sudden drop in the peak power output

of the cell and there was a revival of the cell when the flow rates were decreased. This can be

mainly due to the mass transportation and polarization losses in the cell due to product

accumulation at the cathode as we can clearly see that the peak power value increased when

the input gasses are sent at a slower rate.

The peak power at higher flow rate was found to be 152.9 mWcm-2 at 0.38V with current

density of 399 mAcm-2 and the revived cell peak power at lower flow rates was achieved to

be 177.8 mWcm-2 at 0.32 V with a current density of 546 mAcm-2. It can be clearly seen that

51

there is a loss of peak power current at higher flow rates which might have been caused by

the transportation and/or concentration losses.

All Temperatures:

34 Pt/Graphene (NaBH4 Red.) Cell Performance at All Temperatures

Temperature Current Density Voltage Peak Power

40 456 0.36 165.8

50 597 0.28 167.6

60 636 0.34 218.9

70 648 0.36 235.7

80 399 0.38 152.9

3 Polarization Peak Power Results at All Temperatures of Graphene/Pt With NaBH4

Reduction

52

4.1.2.2 Electrochemical Impedance Spectroscopy Results and Comparison

35 Impedance Plot at All Temperatures

The nyquist trend indicates that the impedance is decreasing consistently with peak power but

the trend was not found to be consistent with temperature unlike the previous sample. The

values of polarization resistances and their relation to maximum power output at a

temperature are discussed below.

53

(a) (b)

36 Impedance and Maximum Power Plots vs Temperature: (a) Maximum Power Density vs

Temperature; (b) Impedance vs Temperature

Temperature (oC) Polarization Impedance (m)

40 273.7

50 314.4

60 261.3

70 249.2

80 289.5

4 EIS Results At All Temperatures of Graphene/Pt With NaBH4 Reduction

It can be observed from the trend that the impedance is not consistent with temperature but is

consistent with the voltage drops and current decrements at the peak power performance.

This trend can be more extensively studied and process can be improved to stabilize the

sample.

54

4.1.3 Results Discussion and Future Work

It is observed from various results discussed in section 4.1.1 and 4.1.2. The maximum

performance achieved for samples in 4.1.1 and 4.1.2 respectively were 220 mWcm-2 @ 80oC

and 235mWcm-2 @ 70oC. From the previous work a maximum power density was achieved

to be 455mWcm-2 [83] but that was at higher loading of the catalyst of 0.6mgcm-2 on cathode

side and 0.4mgcm-2 on the anode part. Another work which used reflux method of adding pt

to graphene showed a maximum performance of about 104mWcm-2 [89] which is low

compared to the performance achieved in this research work. There is a role being played by

the method of manufacturing graphene and the reducing agents used during the synthesis of

Pt decorated graphene. So the process needs be improvised and the best method of decorating

pt and the best method of making graphene must be determined using various extensive

characterizations apart from the polarization. Characterizations such as TEM and XRD are in

progress at present. Various other research focuses on these samples can be studying the

effect of pyrolysis at different temperatures, various concentrations of reducing agents and

doped graphene materials such as N-Graphene on the performance of the fuel cell.

4.2 Tokuyama A901 Membrane Performance Results

4.2.1 Tokuyama A901 AMFC Membrane Performance With Pt/C Catalyst

37 A901 AMFC Polarization with Pt/C Catalyst

55

The A901 sample with Pt/C catalyst testing was very peculiar the temperature had to be

increased very slowly to stabilize the output of the cell. The best performance was achieved

at 60oC and the best performance peak power was 217 mWcm-2 which is very high compared

to the results of A201 for the same catalyst. This showed promising results that A901 can

perform better than A201 AMFC membrane.

4.2.2 Tokuyama A901 Membrane Performance Results with Iron and Cobalt

Pthalocyanine on MWCNTs

Both Iron and Cobalt Pthalocyanine did produce any current output from the cell. This

proved that there was no catalyst surface activity on the surface of the MWCNTs. This

materials need to be extensively researched as discussed in literature review and performance

needs to be studied. The reason for low surface activity of the catalyst is still unknown, this is

the first step that needs to be confirmed before proceeding with further testing.

56

4.3 Polarization Results of Low Loaded Commercial Catalyst With 5nm Cobalt Thin

Film Cathode

38 CO Sputtered Sample Polarization Curves

The Co Sputtered sample on 0.2 mgcm-2 Pt loaded cathode results are as noted above. The

maximum power density output of 413 mWcm-2 produced at 0.45 V with a current density of

1038 mAcm-2 at 80oC operational temperature. At the same operational setting the catalyst

with 0.4 mgcm-2 loading on the cathode has generated a maximum power of 476 mWcm-2 at

a voltage of 0.4 V with a current density of 1197 mAcm-2. The voltage at maximum power

for Co sputtered and non-sputtered sample is observed to be 0.45 and 0.4 V respectively. This

proves that the voltage drop is decreased for the sputtered sample. This might decrease the

output but the catalyst will be more durable. This technique when coupled with highly

57

durable nanomaterials based catalysts, the durability standards set by department of energy

can be achieved.

4.4 Polarization of Organometallic Molecular (Ni, Ph, Bz) Complexes

The present results involve a series of experimental results of 4 different organometallic

molecular complexes. The four complexes are as follows:

Sample 1: Ni-(Ph2Ph2)2

Sample 2: Ni-(Ph2Bz2)2

Sample 3: Ni-(Ph2Ph2)2 – With a carbon black support

Sample 4: Ni-(Ph2Bz2)2 – With carbon black support

All these complexes are for reference and the actual composition is not known truly. The

purpose of this testing is to evaluate the performance of the given samples. I determined the

optimum operational conditions and best performance of each sample to understand the best

sample made.

The performance levels of these samples are generally measured in µWcm-2 because of the

low surface activity of the catalytic materials. The following results discuss about the

performance levels of each samples with a loading of 1mgcm-2 loading on the cathode and

0.2 mgcm-2 Pt/C on the anode.

58

SAMPLE 1 PERFORMANCE:

39 Organometallic Molecular Catalyst Sample 1 Polarization

From the polarization plot it can be clearly concluded that the peak power density of 0.2

mWcm-2 is achieved only at voltage below 0.1 V and current below 3 mAcm-2 at 60oC. This

can be mainly due to the lack of activity of the catalyst or its low oxygen reduction

capabilities which are quite possible because of its non-noble characteristics.

59

SAMPLE 2 PERFORMANCE RESULTS:

For sample 2 the initial testing indicated that it is the second best performing sample. So the

tests were repeated and the temperatures of operation were increased therefore we have two

set of results to discuss.

40 Organometallic Molecular Catalyst Sample 2 Polarization 1

The peak power density in this case is achieved at a better voltage level than sample 1. The

voltage remained just above 0.1 V at a lower current value. But still considering its non-noble

charateristics the performance is very low at maximum power density of 0.2 mWcm-2. But

the retest results showed more promissing values as shown and tabulated below.

60


Temperature

(oC)

Peak Power Current

Density(mAcm-2)

Peak Power Voltage

(V)

Peak power

(mWcm-2)

40 3.12 0.296 0.92

50 2.14 0.35 0.75

60 3.65 0.276 1

70 8.2 0.196 1.62

80 7.88 0.236 1.86

5 Organometallic Molecular Catalyst Sample 2 Polarization 2 Peak Power Values

The best performance was achieved at 80oC with a maximum peak power of 1.86 mWcm-2.

This is less but a comparative step forward.

61


For sample 3 the initial testing indicated that it is the best performing sample. So the tests

were repeated and the temperatures of operation were increased therefore we have two set of

results to discuss.


The peak power density in this case is achieved at a better voltage level than sample 2. The

voltage remained just above 0.1 V at a lower current value. But still considering its non-noble

characteristics the performance is very low at maximum power density of 1.2 mWcm-2,

Which is close to six times that of sample 2. But the retest results showed more promising

values as shown and tabulated below, and there was a huge boost in the power performance.

62


Temperature

(oC)

Peak Power Current

Density(mAcm-2)

Peak Power Voltage

(V)

Peak power

(mWcm-2)

40 85.9 0.27 23.2

50 80.8 0.34 27.4

60 162.3 0.3 48.9

70 157.7 0.3 47.3

80 197.5 0.31 61.2

6 Organometallic Molecular Catalyst Sample 3 Polarization 2 Peak Power Values

The sample 3 catalyst showed a very high performance and a very promising result for

replacing platinum with non-noble organometallic molecular catalysts. The sample produced

a peak power of 61.2mWcm-2 from a very cheap organic catalyst.

63


44 Organometallic Molecular Catalyst Sample 4 Polarization

Sample 4 performance was the least promising of all producing 0.16 mWcm-2 peak power

performance at less than 0.1 V.

All the samples can be tested for more properties of oxygen reduction and high temperature

performance. The process of synthesizing and some more samples for testing are in the

process of being obtained from our source for deep evaluation.

64

4.5 Four Point Probe PVC and PVA Membrane Testing

45 Nafion 212 Membrane Test Results at 30oC

As discussed in section 3.5 of chapter 3, the membrane is tested according to the procedure

and a plot is obtained while testing the membranes which looks similar to the figure above.

From the resultant I-V graph obtained the slope of the line is found out which gives the

resistance(R) value needed for calibration of conductivity as discussed in section 3.5. The

value is substituted and all other values are known. This gives the conductivity of the

membrane being tested.

Various PVA and PVC with different concentrations were tested in the lab and their resultant

In-Plane conductivities are tabulated as follows.

65

PVC MEMBRANE IN-PLANE CONDUCTIVITY RESULTS:

Sample

Measurements Conductivity ( mScm-1)

L W T 30oC 50oC 80oC

PVC 6 (STABLE IN H2O) 0.5 0.5 0.03 0.955 1.15 2.90

PVC 61(STABLE IN H2O) 0.5 0.5 0.02 0.914 1.99 4.35

PVC 8 0.5 0.5 0.1 1.33 2.54 2.57

NAFION 212 0.5 0.5 0.0125 53.20 79.01 104.91

7 PVA Membrane In-Plane Conductivity Results

The best operation temperature of each membrane is the best conductivity result of the

membrane. In the PVC membranes the maximum conductivity was attained generally at

80oC. Even though the conductivity was increasing the value nowhere close to the conduction

value of nafion. The same goes with the PVA membranes as shown below.

PVA MEMBRANE IN-PLANE CONDUCTIVITY RESULTS:

Sample

Measurements Conductivity ( mScm-1)

L W T 30oC 50oC 80oC

PVA-S 0.5 0.5 0.0125 0.91 1.51 1.60

PVA-CMC 0.5 0.5 0.01 2.42 2.90 3.57

NAFION 212 0.5 0.5 0.0125 53.20 79.01 104.90

8 PVC Membrane In-Plane Conductivity Results

66

4.6 Battery Test Results

AUTOMATED TESTED 100 AH SEALED LEAD ACID NEW BATTERY TEST

RESULTS:

46 Charge and Discharge Capacities of SLA 100AH New Battery at C/5 rate (Auto.)

Initially there was a fluctuation in the charge discharge capacity of the battery as the current

battery was a shelved battery but in a new condition. Prior to this testing it was run for a few

cycles using manual charge methods to check the health. Later on the fluctuations slowed

down and the battery was discharging at a constant decrement in its value for each cycle as

expected. This may be due to the uniformity of the automated testing process and very few

anomalies. This determines that the process adopted for testing is very safe and clean.

67

47 Impedance Values of SLA 100AH New Battery at C/5 rate (Auto.)

As discussed earlier the value of the impedance was initially low and then shot up when the

cycle was stabilizing the battery. From then on it’s continuing on its recovery as we can see

that the impedance keeps decreasing from cycle to cycle. This trend will change to increasing

impedance once the battery is completely stabilized. Once the trend is stabilized the health of

the battery can then be monitored continuously.

68

SEMI- AUTOMATED TESTED 100 AH SEALED LEAD ACID OLD BATTERY TEST

RESULTS:

48 Discharge Capacities of SLA 100AH Old Battery

In this case the battery is cycled at 15A charging current and discharged using a very low

amperage of 8A. This improves the capacity when compared to the previous battery. From

the plot above it can be seen that the discharge capacity is very slowly decreasing but it’s

very high due to low amperage and deep discharge.

69

49 Impedance Values of SLA 100AH OLD Battery

As this was also a shelved battery, the battery impedance started decreasing from cycle to

cycle as it was recovering and improving its chemical kinetics. The value continued to

decrease until cycle 5 where it stabilized and from the next cycle the battery impedance

started increasing. From then on the impedance value can be monitored to find the health of

the battery.

70

4.7 Solar Thermal Metal Corrosion Test Results

The weight loss was measured after cleaning each sample according to the ASTM standard

for cleaning corroded alloys. The C-276 sample was washed in a dilute HCL solution along

with DI water whereas the SS-304 sample was washed using HNO3 (dil.) and DI water by

ultrasonicating in each for 20 minutes respectively.

The following weight loss was observed after 5 weeks of testing of each sample.

Corrosion of C-276 in 1:1 Nacl: KCL salt at 800oC for 5 weeks:

50 Corrosion Weight Loss of C276 at 800oC (Nacl+KCl)

The figure showed that there is a weight loss in each sample of C-276 present in the molten

solution as expected. The corrosion rate could not be calibrated because the effective surface

area of the metal was unknown. But the weight loss % gives an effective idea that this alloy

corrodes badly in Nacl+KCl salt solution.

71

Corrosion of SS-304 in 1:1 Nacl: KCL salt at 800oC for 5 weeks:

51 Corrosion Weight Loss of SS-304 at 800oC (Nacl+KCl)

The effective weight loss of each sample of SS-304 was much lower than the weight loss of

C276 in the same molten salt. The corrosion rate is unknown but it is proven that SS-304

corrodes less than C-276 in the present molten salt material of (1:1) KCl: Nacl.

0.0191

0.0397

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

1 2

Wei

ght

Loss

(g)

SS-304 Sample

SS-304 CORROSION TEST (1:1 NaCl:KCl) @ 800oC -5 weeks

72

Corrosion of C-276 in KCl+NaCl+Zncl2 molten salt at 900oC for 5 weeks:

52 Corrosion Weight Loss of C-276 at 900oC (Nacl+KCl+ZnCl2)

It can be clearly seen from the weight loss graph that there is a weight gain in the sample

rather than loss. This generally happens in corrosion experiments due to oxide layer

formation on the corroded part of the metal. The material on the metal will be tested to know

which oxide is actually forming with the help of Scanning Electron Micoscopy (SEM).

-0.09

-0.07

-0.05

-0.03

-0.01

0.01

0.03

0.05

0.07

1 2

Wei

ght

Loss

(g)

Sample

C-276 CORROSION TEST (NaCl+KCl+ZnCl2) @ 900oC -5 weeks

73

CHAPTER 5

CONCLUSION AND DISCUSSION

5.1 Overview

Graphene oxide synthesis was performed successfully with an optimized process for ASU

fuel cell laboratory. Graphene was synthesized successfully in the laboratory using thermal

shock and Inert gas exfoliation method. Graphene prepared was decorated with Platinum

using a two phase transfer and reduction technique previously employed for decorating

MWCNTs. Two different reducing agents were used to determine the best reducing agent in

the process adapted to decorate graphene. The performance of the catalyst in the fuel cell has

been observed and it has been determined that NaBH4 reduced Pt/Graphene (Peak Power:

235mWcm-2) performs slightly well than the one reduced by HCOONa (Peak Power:

220mWcm-2) previously employed in Pt decoration of MWCNTs. The research also provides

the steps of focus to improve the activity of the PT/Graphene catalyst to bring out the best

performance at low cost. Electrochemical Impedance Spectroscopy studies were performed

on each sample while testing at different temperatures to understand the losses that are

reducing the power output of the fuel cell.

The method of coating the fuel cell catalysts with thin film has been successfully studied. It’s

proved that the low Pt loaded catalyst can still perform closely to a high Pt loaded catalyst

when coupled with an active thin film which helps in lower voltage degradation over time.

Cheaper ways of deposition can be studied to effectively bring down the catalyst cost in the

fuel cell and other low loaded catalysts can also be studied along with the thin film coating to

see the effective degradation improvement of the fuel cell with the help of thin film

technology.

74

The performance of Pt/C with Anion exchange membrane A901 has been studied and it’s

evident that A901 performs better than its precursor A201. Activity studies need to be done

on using organometallic catalysts performance with the same AMFC membrane. The Pt/C

catalyst in cathode and anode produced a peak power of 217 mWcm-2.

From the given four materials containing Ni-Ph-Bz complexes, it has been found out that the

third sample given has the most activity and it produced a promising peak power density of

60mWcm-2 which is considered very high for such organometallic complexes in acidic media

(PEMFC).

Automated testing for batteries was set up and two utility level batteries with 100 AH

capacity were studied using one ARBIN Automated test station and one semi-automated

computerized battery analyzer. The state health of the battery was determined based on the

charging capacities and Impedance values through Electrochemical Impedance Spectroscopy

(EIS) Studies.

From the corrosion studies on C276 and SS304 in 1:1 Mixture of NaCl: KCl at 800oC, it has

been found that C276 corrodes faster than SS304. From the corrosion studies of C276 in KCl,

NaCl and Zncl2 at 900oC, there was a curious weight gain which probably can happen by the

oxide layer formation.

5.2 Future Work

The future work on fuel cells can mainly be focused on three main things in fuel cells:

1. Improving the surface activity of graphene and overcoming the stacking that might be the

major cause of lower active catalyst. A better dispersion during the addition of Pt onto the

surface would be a good way of approach.

2. Studying the effect of various concentrations of reducing agent in the process of two phase

transfer technique.

75

3. Studying the effect of graphene produced by various ways and finding the best possible

method to overcome the multi-layer stacking as much as possible.

4. Studying the effect of various pyrolysis temperatures on Pt/graphene and finding the best

and optimum temperature to enhance the performance to the maximum level possible.

5. Surface morphology studies for graphene decorated with Pt

5. Studying the causes that are effecting the activity of the organometallic catalysts on the

surface of MWCNTs for Anion Exchange Membrane Fuel Cells (A901).

6. Studying the performance of Phthalocyanines with graphene support for comparison with

MWCNTs performance as a support in alkaline media.

7. Studying various thin film materials which can be used to improve the durability of

catalysts in acidic media without disturbing the activity of the catalyst.

8. Studying and evaluating alternative membranes for Alkaline and Acidic Media.

76

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