DEVELOPMENT OF DIRECT ETHANOL FUEL CELL

by

HIRALAL PRAMANIK

Chemical Engineering Department

Submitted

in fulfillment of the requirements of the degree of

Doctor of Philosophy

to the

INDIAN INSTITUTE OF TECHNOLOGY DELHI

June 2007

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Dedicated to my parents,

wife and son

Direct. Ethanol Fuel Cell Certificate

CERTIFICATE

This is to certify that the thesis entitled Development of direct ethanol fuel cell, being

submitted by Mr. Hiralal Pramanik to the Indian Institute of Technology Delhi is a

record of bonafide research work carried out by him. He has worked under my guidance

and supervision and has fulfilled the requirements, which to my knowledge, has reached

requisite standard for the submission of this thesis. The results contained in this thesis

have not been submitted in part or full to any University or Institute for the award of any

degree or diploma.

29- • 06 - OR— (Dr. Suddhasatwa Basu)

Associate Professor

Department of Chemical Engineering

Indian Institute of Technology Delhi

New Delhi-110016, India.

Direct Ethanol Fuel Cell Acknowledgements

ACKNOWLEDGEMENTS

First of all, I would like to express my sincere gratitude to my supervisor professor

Suddhasatwa Basu for his intellectual guidance, dedicated interest, generous support,

immense patience, and continuous encouragement throughout this research work.

Professor Basu has devoted his invaluable time to me for discussions and motivation.

Whenever I approached to him for academic or personal discussions, he was always

ready with a helping hand. I appreciate his approach to tackle the problem in a given

situation. He has improved my research skills, mental strength and prepared me for future

challenges.

I am highly thankful to Professor T.R. Rao and Professor B.K. Guha for their highly

valuable suggestions and discussions on technical issues particularly in the

comprehensive examinations. Professor (Ms.) V. Choudhary helped me a lot, by

providing good knowledge on polymer membrane during comprehensive and synopsis

examinations. Professor S. K. Gupta (Head of the Department), Professor A. K. Gupta

and Professor A. N. Bhaskarwar helped me immensely, whenever I was in need. I

sincerely acknowledge Dr. S. Roy and Dr. V. V. Krishnan for their fruitful discussion and

well suggestion on fuel cell. I am also grateful to all the faculty members for their

cooperation as and when needed.

I thank Ministry of Non-Conventional Energy Sources, Government of India, for

supporting financially for the research project on Direct Ethanol Fuel Cell.

Direct Ethanol Fuel Cell Acknowledgements

I thank to the non-teaching staff of Chemical Engineering Department for their helpful

hands, Industrial Design and Development Centre (IDDC) for fabricating the fuel cell,

CPSE and Textile Department (IIT Delhi) for providing me the PEEK membranes and

SEM facility.

I must express my sincere respect towards my parents and in-laws. I express gratitude

from the core of my heart to my wife and son, who have shown tremendous patience and

allowed me to carry out research work. Long hours of devotion at laboratory, would not

have been possible without their positive thinking and tremendous support.

I am very thankful to all of my lab mates and colleagues specially Mr. Amit Kumar

Gupta, Mr. Sandeep Biswas, Mr. Anshuman Agarwal, Mr. Omprakash Sahoo and other

M. Tech. and B. Tech. students.

Above all, I am especially thankful to the almighty God for whom I gathered the strength

and determination during the course of my work.

44^' fig, tAe 20 o (HIRALAL PRAMANIK)

Direct Ethanol Fuel Cell Abstract

ABSTRACT Energy independence is the key to the economic growth and development of any country.

The energy needs are generally provided from fossils fuel using internal combustion

engine and thermal power plant. The problems of limited resources and environmental

pollution by fossil fuel have given momentum to think over the alternative energy

generating methods using renewable resources. The fuel cell technology is found very

promising device for converting chemical energy into electrical energy using hydrogen or

hydrogen rich organic and inorganic compounds. Towards this approach, a direct ethanol

fuel cell is developed for the use of ethanol directly as fuel. The use of ethanol fuel in the

half-cell studies in acid medium and as well as scanty literature on fuel cell are reported

but the complete analyses are not discussed in the open literature.

The electrode prepared using noble metal electrode-catalysts, Pt-Ru (40%:20% by wt.)/C

or Pt-black HSA or Pt (40% by wt.)/C, were tested as anode and cathode. The electrodes

are prepared by spreading electrode-catalysts slurry on the carbon paper using paint brush

technique and the electrodes were sintered at high temperature. The sintered electrodes

are characterized by scanning electron micrography and cyclic voltammetry in half-cell

mode using three-electrode cell assembly. The oxidation and reduction reaction

mechanisms at anode and cathode are derived based on analyses of the reaction products,

results of cyclic voltammetry and literature data for the ethanol fuel under study.

The electrodes prepared were placed on either side of the cast Nafion® membrane and hot

pressed to prepare Membrane Electrode Assembly (MEA). The prepared membrane

Direct Ethanol Fuel Cell Abstract

electrode assembly was used to fabricate the direct ethanol fuel cell. A stainless steel

plate or a Ni-mesh was used as current collector. The current density-cell voltage

characteristics of the cell was determined by measuring voltage and current by varying

load. The experimental parameters studied are concentration of ethanol, different type of

electrode-catalysts at anode and cathode., electrode-catalysts loading, temperature,

oxidant at cathode (air/oxygen), such that maximum power density is obtained. It should

be noted that the cell was operated under temperature gradient. The maximum power

density obtained is 10.27 mW cm -2 for 2M ethanol concentration at a temperature of 90

°C anode and 60 °C cathode with Pt-Ru (40%:20% by wt.)/C anode and Pt-black HSA

cathode with 1 mg/cm2 of loading. The maximum open circuit voltage of 0.815V was

obtained for 2M ethanol with Pt-Ru (40%:20% by wt.)/C anode at 90 °C and Pt-black

HSA cathode at 60 °C. The cell performance increases initially with the increase in

ethanol concentrations from 1M to 2M and then it decreases with further increase in

ethanol concentration. The Pt-Ru (40%:20% by wt.)/C at anode and Pt-black HSA at

cathode give best performance in terms of power density obtained. The fuel cell

performance improves with the increase in anode and cathode electrode-catalysts loading

however beyond electrode-catalysts loading of 1 mg cm -2 the performance does not

increase appreciably. The performance of DEFC increases with the increase in

temperature because of higher reaction rate kinetics and decrease in activation

overpotential. The maximum cell performance is observed at a temperature of anode

90 °C and cathode 60 °C. As temperature is further increased, the performance of direct

ethanol fuel cell decreases. The DEFC performance was checked with different types of

polymer electrolyte membrane (Nafion® SE-5112, 80% and 63% sulfonated polyether

Direct Ethanol Fuel Cell Abstract

ether ketone membranes). MEA prepared from Nafion® membrane gives higher

performance of DEFC compared to that prepared from 80% and 63 % sulfonated PEEK

membranes. The direct ethanol fuel cell performance increases significantly with the use

of sulfuric acid in ethanol compared to that of no sulfuric acid use. However, the DEFC

performance increases slightly with the increase in sulfuric acid proportion in ethanol.

A mathematical model for the direct ethanol fuel cell is developed based on reaction

mechanism proposed earlier. The model takes into account activation, ohmic and

concentration overpotentials and it provides cell voltage at a given current density. The

model prediction is in reasonable agreement with the experimental data on j-v

characteristics. The influence of process variables such as, ethanol concentration and cell

temperature on the prediction of cell performance is reasonably reflected in the model.

The stability test of direct ethanol fuel cell was performed with different anode electrode-

catalysts (Pt-Ru/C, Pt-black and Pt/C of 1 mg cm-2) for 60 hours at a constant load to

analyse the durability of the DEFC. Cathode was made of Pt-black HSA. The voltage of

0.570V, 0.470V and 0.250V were obtained at a current density of 10.70 mA cm-2,

10 mA cm-2 and 8 mA cm-2 for Pt-Ru (40%:20% by wt.)/C, Pt-black HSA and Pt (40%

by wt.)/C, respectively. The calculated efficiency of direct ethanol fuel cell with Pt-Ru/C

(1 mg/cm2) anode and Pt-black HSA (1 mg/cm2) cathode is about 0.30 at a maximum

power density of 7.83 mW cm-2 (temperature 42 °C ; pressure 1 bar). Thus, it is needless

to say, DEFC based on PEM technology could someday be used to draw motive power

(automobile) and as well as stationary power plant.

Direct Ethanol Fuel Cell Contents

CONTENTS

Page No.

Contents ix

List of Figures xiii

List of Tables xxi

Nomenclature xxii

Chapter 1: Introduction 1-7

Chapter 2: Literature Review and Objectives 8-33

2.1 Literature Review 8

2.1.1 Electrode Materials 8

2.1.1.1 Anode Electrode-catalyst 8

2.1.1.2 Cathode Electrode-catalyst 9

2.1.2 Electrode Fabrication Method and Analyses 10

2.1.3 Electrolyte 11

2.1.4 Half-cell Analyses 20

2.1.4.1 Anode 20

2.1.4.2 Cathode 24

2.1.5 Cell Performance 27

2.2. Objectives 32

Chapter 3: Experimental 34-46

3.1 Material 34

3.2 Experimental Setup 37

3.2.1 Half-cell Analyses 37

ix

Direct Ethanol Fuel Cell Contents

3.2.2 Direct Ethanol Fuel Cell (DEFC) 39

3.3 Method 41

3.3.1 Membrane Preparation 41

3.3.2 Preparation of Anode, Cathode and Membrane 42

Electrode Assembly (MEA)

3.3.3 SEM of Electrodes 43

3.3.4 Half-cell Analyses Using Potentiostat 44

3.3.5 Direct Ethanol Fuel Cell 45

3.3.6 Stability of Direct Ethanol Fuel Cell 46

3.4 Reactant and Product Analyses 46

3.4.1 Estimation of Exhaust Ethanol Mixture 46

Chapter 4: Model Development 47-63

4.1 Introduction 47

4.2 Activation Overpotentials 48

4.2.1 Model for Ethanol Fuel 49

4.3 Ohmic Polarization 52

4.4 Concentration Overpotentials 53

4.4.1 Anode 53

4.4.2 Cathode 59

4.5 Model Equation 62

Chapter 5: Results and Discussion 64-117

5.1 Electrode Morphology 64

5.1.1 Anode Electrode 64

Direct Ethanol Fuel Cell Contents

5.1.2 Cathode Electrode 68

5.2 Half Cell Study 70

5.2.1 Anode 70

5.2.1.1 Effect of Sean Rate 70

5.2.1.2 Effect of Ethanol Concentration 74

5.2.1.3 Effect of Electrode-catalysts 77

5.2.1.4 Effect of Electrode-catalyst Loading 79

5.2.2 Cathode 80

5.3 Cell Performance 82

5.3.1 Effect of Ethanol Concentration 82

5.3.2 Type of Electrode-catalyst 88

5.3.3 Anode Electrode-catalyst Loading 92

5.3.4 Cathode-electrode-catalysts Loading 94

5.3.5 Effect of Temperature 96

5.3.6 Oxidant (Air/02) at Cathode 100

5.3.7 Effect of Carbon Paper 102

5.3.8 Effect of Acid Concentration in Ethanol 104

5.3.9 Different Types of Proton Exchange Membranes 106

5.4 Stability of the Direct Ethanol Fuel Cell 108

5.5 Efficiency of the Direct Ethanol Fuel Cell 109

5.6 Model Prediction ... 111

5.6.1 Ethanol Concentration 111

5.6.2 Temperature 113

xi

Direct Ethanol Fuel Cell Contents

5.6.3 Model Parameters

Chapter 6: Summary and Conclusions

115

118-124

6.1 Fuel Cell Components and Constructions 118

6.2 SEM and Half-call Analyses 119

6.3 Direct Ethanol Fuel Cell Performance 120

6.4 Model Development and Prediction 123

6.5 Future Scope 123

Appendices 125-131

Appendix Al Al .a Photograph of Direct Ethanol Fuel Cell Setup 125

Appendix A2 A2.1 Effect of Ethanol Concentration 126

A2.2 Type of Electrode-catalyst 129

References 132-146

About the Author 147

xii