Post on 06-Feb-2023
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
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