Development of Platinum-based Bimetallic Cathode Electrocatalysts for Proton Exchange Membrane Fuel Cell Application (PhD Thesis)
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Indian Institute of Technology (BHU)
2023
Abhay Pratap Singh
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This thesis details the development of platinum-based bimetallic cathode electrocatalysts for proton exchange membrane fuel cell applications. It covers material synthesis, physical and electrochemical characterization, and performance evaluation. The research was conducted at the Indian Institute of Technology (Banaras Hindu University).
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Development of Platinum-based Bimetallic Cathode Electrocatalysts for Proton Exchange Membrane Fuel Cell Application Thesis submitted in partial fulfilment Award of Degree Doctor of Philosophy...
Development of Platinum-based Bimetallic Cathode Electrocatalysts for Proton Exchange Membrane Fuel Cell Application Thesis submitted in partial fulfilment Award of Degree Doctor of Philosophy by ABHAY PRATAP SINGH DEPARTMENT OF CHEMICAL ENGINEERING & TECHNOLOGY INDIAN INSTITUTE OF TECHNOLOGY (BANARAS HINDU UNIVERSITY) VARANASI-221005 Roll No: 17041008 2023 Copyright © Indian Institute of Technology (Banaras Hindu University), Varanasi - 221005, India. All rights reserved 2023 ii CERTIFICATE It is certified that the work contained in the thesis titled “Development of Platinum-based bimetallic cathode electrocatalysts for Proton Exchange Membrane fuel cell application” by “Abhay Pratap Singh” has been carried out under my supervision and that this work has not been submitted elsewhere for a degree. It is further certified that the student has fulfilled all the requirements of Comprehensive Examination, Candidacy and SOTA for the award of Ph.D. Degree. iii DECLARATION BY THE CANDIDATE I, "Abhay Pratap Singh", certify that the work embodied in this thesis is my own bona fide work and carried out by me under the supervision of "Prof. Hiralal Pramanik" from "July 2017 to July 2023” at the “Department of Chemical Engineering & Technology”, Indian Institute of Technology (BHU), Varanasi. The matter embodied in this thesis has not been submitted for the award of any other degree/diploma. I declare that I have faithfully acknowledged and given credits to the research workers wherever their works have been cited in my work in this thesis. I further declare that I have not wilfully copied any other's work, paragraphs, text, data, results, etc., reported in journals, books, magazines, reports dissertations, theses, etc., or available at websites and have not included them in this thesis and have not cited as my own work. Date: Place: (Abhay Pratap Singh) CERTIFICATE BY THE SUPERVISOR It is certified that the above statement made by the student is correct to the best of my knowledge. iv COPYRIGHT TRANSFER CERTIFICATE Title of the Thesis: “Development of Platinum-based bimetallic cathode electrocatalysts for Proton Exchange Membrane fuel cell application” Name of the student: Mr. Abhay Pratap Singh Copyright Transfer The undersigned hereby assigns to the Indian Institute of Technology (Banaras Hindu University) Varanasi all rights under copyright that may exist in and for the above thesis submitted for the award of the “Ph.D. Degree”. Date: Place: (Abhay Pratap Singh) Note: However, the author may reproduce or authorize others to reproduce material extracted verbatim from the thesis or derivative of the thesis for author's personal use provided that the source and the Institute's copyright notice are indicated. v Dedicated to My Beloved Parents & Family Members Acknowledgement ACKNOWLEDGEMENT These years at Varanasi were quite essential to me, and looking back, I can see how much I have matured as a person and as a research student. If I've made it this far in my Ph.D. path, it's because of all the people who have supported me and whom I want to express my gratitude to: Prof. Hiralal Pramanik, my supervisor, for believing in me as a researcher and allowing me to pursue a Ph.D. to generate useful ideas. Thank you so much for leading me in the right direction when I needed it and for teaching me the value of taking a broad perspective on things. Thank you for teaching me all I needed to know to accomplish my Ph.D.: how to carefully apply ideas in the lab, how to network, how to write manuscripts, and how to write my thesis. I owe you respect and gratitude for always being there for me. I can't extend my appreciation to you enough! My sincere thanks to Dr. Sweta to step in as my co-supervisor and encouraging my work. Thank you for always being ready to listen to my progress and questions and for always going out of your way to help me. I also express my heartiest thanks to Prof. Manoj Kumar Mondal, Head of the Department, Department of Chemical Engineering & Technology, Indian Institute of Technology (BHU) for providing essential research facilities and encouragement during the research work. I would especially thank Prof. Y.C. Sharma and Prof. M.K. Mondal, Indian Institute of Technology, Banaras Hindu University. Without the help of them, my project may not be completed. I am very thankful for their valuable advice & guidance, RPEC, DPGC members of the Chemical Engineering & Technology Department for their useful suggestions during my research work at the institute. The instrumental facilities from CIFC (IIT-BHU) Varanasi are gratefully acknowledged. Indian Institute of Technology (BHU), Varanasi vii Acknowledgement Thank you to everyone in the Energy Resource Lab for creating such a welcoming environment and for trying to improve the environment! I couldn't ask for nicer senior and junior; Dr. Pramendra Gaurh, Dr. Uday Gupta, Dr. Abhay Chaudhary, Dr. Deoashish Panjiara, Ms. Anjali Verma, Mr. Neeraj Kumar Yadav and Mr. Bhavya Teja Reddy from Energy Resource Lab for their kind help and support. Thank you for your nice comments and smiles, as well as your willingness to share your expertise. I deeply express my gratitude to my parents for their unconditional trust, timely encouragement, and endless patience. It was their love that raised me up again when I got weary. Thank you for making me feel invincible, Mrs. Sushma Singh, my wife and closest friend. Thank you so much for all of your love and support. Every day of my existence is made more important because of you. Date: Place: (Abhay Pratap Singh) Indian Institute of Technology (BHU), Varanasi viii Table of contents TABLE OF CONTENTS Page no. List of Figures xiii List of Tables xvii Nomenclature xix Preface xxi CHAPTER - 1 INTRODUCTION 1 CHAPTER - 2 LITERATURE REVIEW AND OBJECTIVES 13 2.1 Proton exchange membrane fuel cell advancement 13 2.1.1 Main components of proton exchange membrane fuel cell (PEMFC) 15 2.1.1.1 Membrane electrolyte 15 2.1.1.2 Electrodes 17 2.1.1.3 Anode electrocatalyst material 18 2.1.1.4 Cathode electrocatalyst material 20 2.1.1.4.1 Cathode electrocatalyst preparation methods 23 2.1.1.5 Physical Characterizations of synthesized cathode electrocatalyst 26 2.1.1.5.1 X-ray diffraction (XRD) characterization 26 2.1.1.5.2 Scanning electron microscope (SEM) characterization 28 2.1.1.5.3 Energy dispersive X-ray (EDX) analysis 28 2.1.1.5.4 Transmission electron microscopy (TEM) analysis 29 2.1.1.6 Electrochemical characterization of synthesized cathode electrocatalyst 31 2.1.1.6.1 Cyclic voltammetry (CV) analysis 31 2.1.1.6.2 Electrochemical impedance spectroscopy (EIS) analysis 33 2.1.1.7 Cathode oxidant 35 Indian Institute of Technology (BHU), Varanasi ix Table of contents 2.1.1.8 Performance of cathode electrocatalyst 36 2.2 OBJECTIVES 40 CHAPTER - 3 EXPERIMENTAL 42 3.1 Materials 42 3.2 Electrocatalyst synthesis 47 3.2.1 Synthesis of Pt-Co/CAB cathode electrocatalyst 47 3.2.2 Synthesis of Pt-Ni/CAB cathode electrocatalyst 48 3.3 Physical characterization of Pt-Co/CAB and Pt-Ni/CAB electrocatalyst 50 3.3.1 X-ray diffraction (XRD) 50 3.3.2 Scanning electron microscopy (SEM) and Energy dispersive X-ray spectroscopy (EDX) 51 3.3.3 Transmission electron microscopy (TEM) 51 3.4 Electrochemical characterization of Pt-Co/CAB and Pt-Ni/CAB electrocatalyst 52 3.4.1 Fabrication of electrode for oxygen reduction reaction (ORR) 52 3.4.2 Half-cell studies 53 3.4.3 Electrochemical impedance spectroscopy (EIS) analysis 54 3.5 Single cell experimental setup and method 54 3.6 Stability test 56 CHAPTER - 4 OPTIMIZATION OF PROCESS PARAMETERS BY RSM 58 CHAPTER - 5 RESULTS AND DISCUSSION 62 5.1 Pt-Co(3:1)/CAB cathode electrocatalyst performance evaluation: Part I 62 5.1.1 Physical Characterization 62 5.1.1.1 X-ray diffraction (XRD) analysis 62 5.1.1.2 Scanning electron microscopy (SEM) analysis 65 5.1.1.3 Energy dispersive X-ray (EDX) analysis 67 5.1.1.4 Transmission electron microscopy (TEM) analysis 69 5.1.2 Electrochemical characterization 74 Indian Institute of Technology (BHU), Varanasi x Table of contents 5.1.2.1 Cyclic voltammetry (CV) of cathode electrode 74 5.1.2.1.1 Effect of scan rate 74 5.1.2.1.2 CV study of cathode in oxygen and nitrogen purged electrolyte solution 76 5.1.2.2 Electrochemical impedance spectroscopy (EIS) analysis 78 5.1.3 Performance study of synthesized Pt-Co(3:1)/CAB electrocatalyst in single cell PEMFC 81 5.1.3.1 Comparative performance of cathode electrocatalyst 81 5.1.3.2 Effect of anode loading 83 5.1.3.3 Effect of cathode loading 85 5.1.3.3.1 Pt-Co(3:1)/CAB-EG as cathode electrocatalyst 85 5.1.3.3.2 Pt-Co(3:1)/CAB-DMF as cathode electrocatalyst 86 5.1.3.3.3 Pt-Co(3:1)/CAB-DMSO as cathode electrocatalyst 87 5.1.3.3.4 Pt-Co(3:1)/CAB-W as cathode electrocatalyst 88 5.1.3.4 Effect of temperature in PEMFC 89 5.2 Pt-Ni(3:1)/CAB cathode electrocatalyst performance evaluation: Part II 92 5.2.1 Physical characterization 92 5.2.1.1 X-ray diffraction (XRD) analysis 92 5.2.1.2. SEM-EDX analysis 94 5.2.1.3 Transmission electron microscopy (TEM) analysis 97 5.2.2 Electrochemical characterization of electrocatalyst 101 5.2.2.1 Cyclic voltammetry (CV) analysis 101 5.2.3 Performance study of synthesized Pt-Ni(3:1)/CAB electrocatalyst in single cell PEMFC 103 5.2.3.1 Effect of cathode electrocatalyst type 103 5.2.3.2 Effect of anode loading 105 5.2.3.3 Effect of cathode loading 107 5.2.3.3.1 Pt-Ni(3:1)/CAB-EG as cathode electrocatalyst 107 Indian Institute of Technology (BHU), Varanasi xi Table of contents 5.2.3.3.2 Pt-Ni(3:1)/CAB-DMF as cathode electrocatalyst 108 5.2.3.3.3 Pt-Ni(3:1)/CAB-DMSO as cathode electrocatalyst 109 5.2.3.4 Effect of temperature in PEMFC 110 5.2.4 Process parameter optimization using RSM 113 5.2.4.1 ANOVA and model development 113 5.2.4.2 Process parameter optimization and its effect on response 118 5.2.4.3 Polarization and power density curves 122 5.2.5 Efficiency of the proton exchange membrane fuel cell (PEMFC) 124 5.2.6 Stability test using best cathode electrocatalysts Pt-Co(3:1)/C AB-EG and Pt-Ni(3:1)/CAB-EG in PEMFC 126 CHAPTER - 6 CONCLUSIONS 128 6.1 Cathode electrocatalyst characterization 128 6.1.1 Physical characterization 128 6.1.2 Electrochemical characterization 129 6.2 Single cell performance 130 6.2.3 Optimization of cell parameters using RSM 130 6.3 Future scope 131 REFERENCES 133 Appendix A 152 Appendix B 153 Appendix C 154 Appendix D 155 Appendix E 159 Indian Institute of Technology (BHU), Varanasi xii List of figures LIST OF FIGURES Figure 1.1 Hydrogen/oxygen fuel cell and its reactions based on the proton 5 exchange membrane. Figure 2.1 Three phase assembly formed by electrocatalyst particles, the ionomer 18 and the gas phase in a porous structure, ensuring both electronic and ionic contact as well as gas transport. Figure 2.2 XRD patterns for Pt/C and Pt-M (M= Ni, Co, Cu and Y) electrocatalyst 27 (Hyun et al., 2013). Figure 2.3 Elemental mapping of Pt-Ni-Fe/ICNT/CP (a) C mapping, (b) Fe 29 mapping, (c) Ni mapping, (d) O mapping, and (e) Pt mapping (Litkohi et al., 2017). Figure 2.4 TEM images and corresponding particles size distribution profile of 30 varied Pt and Ni compositions on carbon supported (a) PNC-1, (b) PNC-2, and (c) PNC-3 (Polagani et al., 2023). Figure 2.5 Cyclic voltammetry for Pt-Ru/C, Pt-back HAS and Pt/C cathode in the 33 presence of oxygen in 0.5m HClO4 solution with scan rate of 10 m/Vs at 42 oC (Pramanik and Basu 2011). Figure 2.6 Nyquist plot of the ORR on (a) Pt/TiO2-C, (b) Pt/SnO2-C and (c) Pt/C 35 (Eteck) in O2 saturated solution in acidic solution (Ruiz-Camacho et al., 2017). Figure 3.1 Image of (a) gas diffusion layer (GDL), (b) fabricated cathode for half- 52 cell. Figure 3.2 Schematic of three electrode cell assembly schematic for conducting 53 CV and EIS experiments using a potentiostat galvanostat (PGSTAT). Figure 3.3 Image of membrane electrode assembly (MEA). 55 Figure 3.4 Schematic of proton exchange membrane fuel cell experimental set up. 56 Figure 5.1 XRD pattern of Pt-Co/CAB synthesized electrocatalysts (a) Pt-Co/CAB- 63 DMSO, (b) Pt-Co/CAB-DMF, (c) Pt-Co/CAB-EG and Pt-Co/CAB-W. Figure 5.2 SEM images of Pt-Co/CAB synthesized electrocatalyst (a) Pt-Co/CAB- 66 DMSO, (b) Pt-Co/CAB-DMF, (c) Pt-Co/CAB-EG and (d) Pt-Co/CAB-W. Figure 5.3 EDX images of Pt-Co/CAB synthesized electrocatalyst (a) Pt-Co/CAB- DMSO, (b) Pt-Co/CAB-DMF, (c) Pt-Co/CAB-EG and (d) Pt-Co/CAB-W respectively. Indian Institute of Technology (BHU), Varanasi xiii List of figures Figure 5.4 Pt-Co/CAB-DMSO, (b) Pt-Co/CAB-DMF, (c) Pt-Co/CAB-EG and (d) Pt- 72 Co/CAB-W respectively. Figure 5.5 Cyclic voltammetry for synthesized electrocatalyst (a) Pt-Co/CAB- 76 DMSO, (b) Pt-Co/CAB-DMF, (c) Pt-Co/CAB-EG and (d) Pt-Co/CAB-W respectively of fixed loading 1 mg/cm2 with different scan rates using oxygen saturated 0.5 M HClO4 electrolyte. Figure 5.6 Cyclic voltammetry for synthesized electrocatalyst (a) Pt-Co/CAB- 78 DMSO, (b) Pt-Co/CAB-DMF, (c) Pt-Co/CAB-EG and (d) Pt-Co/CAB-W of fixed loading 1 mg/cm2 at 100 mV/s scan rate using 0.5 M HClO4 electrolyte saturated with nitrogen or oxygen. Figure 5.7a Nyquist plot of synthesized cathode electrocatalysts Pt-Co/CAB- 79 DMSO, Pt-Co/CAB-DMF, and Pt-Co/CAB-EG at 0.85 V in oxygen saturated 0.5 M HClO4; Temperature 30 oC. Figure 5.7b Equivalent circuit diagram corresponds to the Nyquist plot obtained 80 from EIS. Figure 5.8 Polarization and power density curves for commercial anode Pt/C HSA 82 electrocatalyst of loading 1 mg/cm2 and synthesized cathode Pt- Co/CAB-DMSO, Pt-Co/CAB-DMF, Pt-Co/CAB-EG and Pt-Co/CAB-W electrocatalysts of loading 1 mg/cm2 respectively, in proton exchange membrane fuel cell at the operating temperature of 33 oC; Dotted line – power density curves; Solid lines – polarization curves. Figure 5.9 Polarization and power density curves for varying loading of 84 commercial anode Pt/CHSA electrocatalyst and fixed loading of 1 mg/cm2 synthesized Pt-Co/CAB-EG cathode electrocatalyst in proton exchange membrane fuel cell at an operating temperature of 33 oC; Dotted line – power density curves; Solid lines – polarization curves. Figure 5.10 Polarization and power density curves for commercial anode Pt/C HSA 86 of fixed optimum loading of 1 mg/cm2 and synthesized Pt-Co/CAB-EG cathode electrocatalyst of varying loading in proton exchange membrane fuel cell at an operating temperature of 33 oC; Dotted line – power density curves; Solid lines – polarization curves. Figure 5.11 Polarization and power density curves for commercial anode Pt/C HSA 87 of fixed optimum loading of 1 mg/cm2 and synthesized Pt-Co/CAB- DMF cathode electrocatalyst of varying loading in proton exchange membrane fuel cell at an operating temperature of 33 oC; Dotted line – power density curves; Solid lines – polarization curves. Figure 5.12 Polarization and power density curves for commercial anode Pt/C HSA 88 of fixed optimum loading of 1 mg/cm 2and synthesized Pt-Co/CAB- DMSO cathode electrocatalyst of varying loading in proton exchange membrane fuel cell at operating cell temperature of 33 oC; Dotted line – power density curves; Solid lines – polarization curves. Indian Institute of Technology (BHU), Varanasi xiv List of figures Figure 5.13 Polarization and power density curves for commercial anode Pt/C HSA 89 of fixed optimum loading of 1 mg/cm2and synthesized Pt-Co/CAB-W cathode electrocatalyst of varying loading in proton exchange membrane fuel cell at operating cell temperature of 33 oC; Dotted line – power density curves; Solid lines – polarization curves. Figure 5.14 Polarization and power density curves for commercial anode Pt/C HSA 91 electrocatalyst and synthesized Pt-Co/CAB-EG cathode electrocatalyst keeping fixed optimum loading of 1 mg/cm2 at both the electrodes; Dotted line – power density curves; Solid lines – polarization curves. Figure 5.15 XRD patterns of synthesized electrocatalysts Pt-Ni/CAB-DMSO, Pt- 92 Ni/CAB-DMF and Pt-Ni/CAB-EG. Figure 5.16 SEM/EDX images of synthesized electrocatalyst with different 96 solvents (a) Pt-Ni/CAB-DMSO, Pt-Ni/CAB-DMF and Pt-Ni/CAB-EG Figure 5.17 TEM images and corresponding histogram of synthesized 99 electrocatalyst (a) Pt-Ni/CABDMSO, (b) Pt-Ni/CAB-DMF, and (c) Pt- Ni/CAB-EG. Figure 5.18 Cyclic voltammetry for synthesized electrocatalysts (a) Pt-Ni/CAB- 103 DMSO, (b) Pt-Ni/CAB-DMF and (c) Pt-Ni/CAB-EG of fixed loading 1 mg/cm2 with 100 mV/s scan rate using oxygen saturated 0.5 M HClO4 electrolyte; temperature 33 oC. Figure 5.19 Polarization and power density curves for commercial anode Pt/C HSA 105 electrocatalyst of loading 1 mg/cm2 and synthesized cathode Pt- Ni/CAB-DMSO, Pt-Ni/CAB-DMF and Pt-Ni/CAB-EG electrocatalysts of loading 1 mg/cm2 respectively, in proton exchange membrane fuel cell at operating temperature of 33 oC; Dotted line – power density curves; Solid lines – polarization curves. Figure 5.20 Polarization and power density curves for varying loading of 106 commercial anode Pt/CHSA electrocatalyst and fixed loading of 1 mg/cm2 synthesized Pt-Ni/CAB-EG cathode electrocatalyst in proton exchange membrane fuel cell at operating temperature of 33 oC; Dotted line – power density curves; Solid lines – polarization curves. Figure 5.21 Polarization and power density curves for commercial anode Pt/C HSA 108 electrocatalyst of loading 1 mg/cm2 and synthesized cathode Pt- Ni/CAB-EG electrocatalysts of loading 1 mg/cm2 respectively, in proton exchange membrane fuel cell at operating temperature of 33 o C; Dotted line – power density curves; Solid lines – polarization curves. Indian Institute of Technology (BHU), Varanasi xv List of figures Figure 5.22 Polarization and power density curves for commercial anode Pt/C HSA 109 electrocatalyst of loading 1 mg/cm2 and synthesized cathode Pt- Ni/CAB-DMF electrocatalysts of loading 1 mg/cm2 respectively, in proton exchange membrane fuel cell at operating temperature of 33 o C; Dotted line – power density curves; Solid lines – polarization curves. Figure 5.23 Polarization and power density curves for commercial anode Pt/C HSA 110 electrocatalyst of loading 1 mg/cm2 and synthesized cathode Pt- Ni/CAB-DMSO electrocatalysts of loading 1 mg/cm2 respectively, in proton exchange membrane fuel cell at operating temperature of 33 oC; Dotted line – power density curves; Solid lines – polarization curves. Figure 5.24 Polarization and power density curves for commercial anode Pt/C HSA 111 electrocatalyst and synthesized Pt-Ni/CAB-EG cathode electrocatalyst keeping fixed both loading at 1 mg/cm2; Dotted line – power density curves; Solid lines – polarization curves. Figure 5.25 Actual versus model predicted power density comparison. 117 Figure 5.26 Predicted vs. Residual value of power density obtained from PEMFC. 118 Figure 5.27a Three-dimensional (3D) response plots showing the effect of cathode 119 loading (A), cell temperature (B) and their mutual interaction on power density. Figure 5.27b Three-dimensional (3D) response plots showing the effect of cathode 120 loading (A) hydrogen flow rate (C) and their mutual interaction on power density. Figure 5.27c Three-dimensional (3D) response plots showing the effect of cell 121 temperature (B), hydrogen flow rate (C) and their mutual interaction on power density. Figure 5.28a Current density vs. cell voltage and power density curves for optimum 122 condition of cathode electrocatalyst loading of 1.12 mg/cm 2, cell temperature of 60.84 oC and hydrogen flow rate of 49.97 ml/min, Solid line – polarization curves; Dotted line – power density curves. Figure 5.28b Current density vs. cell voltage and power density curves for optimum 124 condition of cathode electrocatalyst loading of 1 mg/cm 2, cell temperature of 55 oC and hydrogen flow rate of 45 ml/min, Solid line – polarization curves; Dotted line – power density curves. Figure 5.29 Stability test of hydrogen based PEMFC using the optimum conditions 127 of operation at constant load at a temperature of 33 oC for the best electrocatalyst Pt-Ni(3:1)/CAB-EG and Pt-Co(3:1)/CAB-EG. Indian Institute of Technology (BHU), Varanasi xvi List of tables LIST OF TABLES Table 2.1 Performance comparison of different types of electrocatalyst for 38 hydrogen fuel in Proton exchange membrane fuel cell. Table 3.1 Properties of dimethyl sulfoxide (SDFCL, India). 43 Table 3.2 Properties of distilled water. 44 Table 3.3 Properties of ethylene glycol (Alfa Aesar, India). 44 Table 3.4 Properties of dimethylformamide (Alfa Aesar, India). 44 Table 3.5 Properties of dimethylformamide (Alfa Aesar, India). 45 Table 3.6 Composition and properties of Nafion® solution (Alfa Aesar, USA). 45 Table 3.7 Properties of PTFE Dispersion (Sigma Aldrich, USA). 46 Table 3.8 Properties of Toray Carbon paper, TGP-H-60 (Alfa Aesar, USA). 46 Table 3.9 Properties of hydrogen fuel (Alfa Aesar, India). 46 Table 4.1 Levels and limits of independent variables studies in the BBD. 60 Table 5.1 Lattice parameters and the particle size at Pt (220) X-ray diffraction 63 peak of Pt-Co/CAB synthesized electrocatalyst. Table 5.2 Surface concentration of synthesized electrocatalyst obtained from EDX 69 analysis. Table 5.3 The average particle size of electrocatalysts from TEM analysis and 70 comparison with XRD average crystallite size. Table 5.4 Particle size distribution of synthesized electrocatalysts by TEM 73 analysis. Table 5.5 Performance parameters of equivalent circuit obtained from Z-view 80 software. Table 5.6 Summary of performance of synthesized Pt-Co/CAB-DMSO, Pt- 82 Co/CAB-DMF, Pt-Co/CAB-EG and Pt-Co/CAB-W cathode electrocatalysts in proton exchange membrane fuel cell at a room temperature of 33 oC. Table 5.7 Summary of performance of the synthesized best cathode Pt-Co/C AB- 91 EG electrocatalyst using optimum loading of 1 mg/cm2 in PEMFC at various operating temperatures. Indian Institute of Technology (BHU), Varanasi xvii List of tables Table 5.8 Lattice parameters and the crystallographic properties at Pt (220) 93 diffraction peak of Pt-Ni/CAB synthesized electrocatalyst. Table 5.9 Surface concentration of synthesized electrocatalyst obtained from EDX 96 analysis. Table 5.10 The average particle size of electrocatalysts from TEM analysis and 99 comparison with XRD average crystallite size. Table 5.11 Particle size distribution of synthesized electrocatalysts by TEM 99 analysis. Table 5.12 Summary of performance of the synthesized best cathode Pt-Ni/C AB- 112 EG electrocatalyst using optimum loading of 1 mg/cm2 in a proton exchange membrane fuel cell (PEMFC) at various operating temperatures. Table 5.13 The BBD arrangement for PEMFC and the corresponding experimental 113 and predicted power density. Table 5.14 ANOVA of the fitted quadratic model for the response. 115 Table 5.15 Comparison of predicted and actual power density at the optimum 123 condition obtained from the model. Table 5.16 Comparison of predicted and actual power density at the random 124 condition obtained from the model. Table 5.17 Efficiency of PEMFC using best Pt-Co(3:1)/-CAB-EG and Pt- 126 Ni(3:1)/CAB-EG cathode electrocatalysts at room temperature (33 oC) and atmospheric pressure (1 atm). Indian Institute of Technology (BHU), Varanasi xviii Nomenclature NOMENCLATURE Abbreviation Meaning ANOVA Analysis of variance BBD Box behnken design CCME Catalyst coated membrane electrode CNT Carbon nanotube CV Cyclic voltammetry 3D Three-dimensional DF Degree of freedom DMF Dimethylformamide DMSO Dimethyl sulfoxide EDX Energy dispersive X-ray analysis EG Ethylene glycol EIS Electrochemical impedance spectroscopy FCA Flow channel area GDL Gas Diffusion Layer HSA High surface area MPD Maximum power density MWCNT Multi-walled carbon nanotube NC N-micro/mesoporous carbon supported OCV Open circuit voltage ORR Oxygen reduction reaction PEMFC Proton exchange membrane fuel cell RSM Response surface methodology SEM Scanning electron microscopy TEM Transmission electron microscopy W Water XRD X-ray diffraction Indian Institute of Technology (BHU), Varanasi xix Abbreviations Greek Symbols Meaning αo Lattice parameter of pure carbon supported Pt Width of the peak (in radians) Linear parameter ii Quadratic parameter ij Interaction parameter Scherrer constant Theta (in degree) 𝜂 Total efficiency 𝜂 Faraday efficiency 𝜂 Heating value efficiency 𝜂 Thermodynamics efficiency 𝜂 Fuel utilization efficiency 𝜂 Electrochemical efficiency Alphabetic symbols Meaning A Cathode loading a Lattice parameter ao Lattice parameter of pure carbon supported Pt B Cell temperature C Hydrogen flow rate CAB Acetylene black dc Average crystallite size dhkl Interplanar distance between two planes of miller indices (hkl) k Number of factors in RSM study N Total number of experiments in RSM study p-value Probability value R2 Coefficient of determination Xi and Xj Independent variables for the studied factor Y Predicted response (maximum power density) Indian Institute of Technology (BHU), Varanasi xx Preface PREFACE The recent past has shown a sharp growth in energy demand as a result of rising global population. The conventional fuels like crude oil, coal, and natural gas, among others, are used to meet energy needs in the domestic and industrial sectors. Recently, the rate at which conventional energy resources are consumed has greatly increased. The major motivation to consider alternative energy sources, however, is the limited storage of conventional energy sources, such as crude oil, coal, and natural gas. The low temperature fuel cell may be considered as better source of energy compared to the other conventional energy sources. It is well known that, hydrogen-based fuel cell has attracted interest due to their potentially low degree of pollution and better electrical efficiency than other alcohol based fuel cells. No better alternative to the conventional energy sources. However, irrespective of any kind of fuel cell it suffers from different types of losses/polarization viz activation losses, ohmic losses, and concentration losses. Activation polarization is due to the slow electrochemical reactions at the electrode surface, where the species are oxidized or reduced in a fuel cell electrode reaction. Low-temperature fuel cells powered by hydrogen are gaining popularity because of their ability to use a proton exchange membrane (PEM) made of a material like Nafion® as an electrolyte with high ionic conductivity. According to numerous published research, oxygen reduction at the cathode is slower in an acidic medium or PEM than anode electro-oxidation of H2 fuel in the presence of a Pt-based electrocatalyst. Slow reduction kinetics at the cathode for a Pt-based electrocatalyst is thus one of the major challenges for the oxygen reduction reaction. Other challenges of proton exchange membrane fuel cell (PEMFC) are proton conductivity at high temperatures (T > 80 oC), notable activation loss, and the high cost of pure Indian Institute of Technology (BHU), Varanasi xxi Preface Pt-based electrocatalyst. Currently, researchers are working very hard to develop a very effective bimetallic cathode electrocatalyst that could reduce the consumption of costly platinum (Pt), reduce activation overpotential and raise the current density to a few folds higher than the existing electrocatalyst. In order to build bimetallic electrocatalysts for oxygen reduction reaction (ORR) at the PEMFC cathode, it is necessary to add other metals, such as Co, Cr, Ni, and W to Pt. This will surely lower the cost of the cathode electrocatalyst and consequently lower the overall fabrication cost of the fuel cell. The platinum (Pt) is a widely used cathode electrocatalyst for the oxygen reduction reaction because it is electrochemically very active. However, Pt-based bimetallic electrocatalysts are not commercially commonplace. As a result, there is an urgent need to synthesize bimetallic Pt-M (where M is Co, Ni, etc.) electrocatalysts to enhance oxygen reduction reaction kinetics and activity. Despite several attempts to create acceptable Pt-based bimetallic electrocatalysts, no scientific work has yet examined the impact of different solvent types on electrocatalyst development. The solvent, which acts as an agent in the preparation of highly active core-shell electrocatalysts and regulates the size and shape of synthesized particles, also plays a significant role in the synthesis of highly active electrocatalysts. Bimetallic Pt-M/C AB (M = Co, Ni) electrocatalysts for efficient ORR in hydrogen-based PEMFC were synthesized using the solvothermal method using four different solvents, namely dimethyl sulphoxide (DMSO), dimethylformamide (DMF), ethylene glycol (EG), and water (W). The EG-based solvothermal method produced a highly effective active cathode electrocatalyst, Pt-Ni/CAB-EG, which displayed the best performance for ORR in a half-cell and single PEMFC out of all four solvents employed in the synthesis of cathode electrocatalysts. Indian Institute of Technology (BHU), Varanasi xxii Preface The acetylene black supported with 20 wt.% metal loading, cathode electrocatalysts Pt-M(3:1)/C AB (M = Co, Ni) were synthesized using platinum (II) acetylacetonate, cobalt (III) acetylacetonate, H2PtCl6.6H2O and NiCl2.6H2O precursors by solvothermal method using four types of solvents namely, dimethyl sulphoxide (DMSO), dimethylformamide (DMF), ethylene glycol (EG) and water (W). The synthesized Pt-based bimetallic electrocatalysts were Pt-Co/C AB-DMSO, Pt-Co/CAB-DMF, Pt-Co/CAB-EG, Pt-Co/CAB-W, Pt-Ni/CAB-DMSO, Pt-Ni/CAB-DMF and Pt-Ni/CAB-EG. The synthesized electrocatalysts were characterized by XRD, SEM, EDX, TEM, and electrochemical techniques (CV and EIS). The anode electrocatalyst was commercial Pt/C HSA (40 wt. %). For electrode preparation, a gas diffusion layer (GDL) was used. The ink was made by combining the necessary amounts of electrocatalyst, isopropanol, Nafion® dispersion, and PTFE dispersion. The prepared ink was painted on carbon paper using a paintbrush for anode and cathode preparation. The experiment was performed to achieve the best cell performance, with synthesized cathode electrocatalyst in PEMFC. The PEMFC operating parameters were optimized using response surface methodology (RSM) using the best cathode electrocatalyst candidate. The XRD analysis confirms, the all synthesized Pt-Co/CAB electrocatalyst were crystalline in structure and show their prominent diffraction peaks of the face-centered cubic (FCC) for Pt at plane 220. This prominent shifting of 2θ proved the incorporation of Co into Pt metal of the FCC structure, which results in alloy formation of Pt-Co/CAB. The Pt-Ni/CAB XRD patterns demonstrated that the Pt-phase in the synthesized electrocatalysts consisted of highly crystalline face-centered cubic (FCC) structure. The lattice parameters of all Pt-Ni/CAB alloy electrocatalysts were between those for pure Pt (0.3924 nm) and pure Ni (0.3523 nm). Peaks for Ni were not observed in the XRD patterns of the Pt-Ni/CAB synthesized electrocatalyst, although their presence could be discarded. The SEM Indian Institute of Technology (BHU), Varanasi xxiii Preface images of the prepared electrocatalyst showed that the particles were uniformly dispersed across the support material and were in the nanometer size range. The EDX analysis was performed to determine the surface composition of all active components and elemental mapping, which reveals the existence of C, Pt, Co, and Ni elements in the synthesized electrocatalyst, Pt-Co/C AB and Pt- Ni/CAB. The TEM study indicated that the particles were between 2 to 20 nm for Pt-Co/C AB and 3 to 6.5 nm for Pt-Ni/CAB in size. The half-cell analysis using CV showed that Pt-Co/C AB-EG and Pt-Ni/CAB-EG had low activation losses as compared to other synthesized electrocatalyst. EIS showed that Pt-Co/CAB-EG had the lowest charge transfer resistance related to the other Pt-Co/C AB electrocatalyst. In the PEMFC, the performance of anode electrocatalysts Pt-Co/C AB and Pt- Ni/CAB of the same compositions was examined. The performance of PEMFC increased with the increase in electrocatalyst loading but beyond the optimum loading, the performance, got decreased due to an increase in the mass transfer resistance for the flow of reactants (hydrogen and oxygen) from the bulk to reaction sites on the electrode surface. A rise in cell operating temperature improved cell performance by increasing reaction kinetics at anode and cathode. Moreover, the mobility of ions improved, at the high temperature, hence ohmic loss decreases. Excessive increase in cell temperature, reduced the PEMFC performance due to dehydration of membrane as well as the electrode surface. The performance of synthesized electrocatalyst Pt-Co/C AB-EG was superior among all the synthesized Pt-Co/CAB electrocatalysts in half-cell, as well as in the single PEMFC. Similarly, Pt-Ni/CAB-EG showed, a better performance than the other synthesized Pt-Ni/C AB electrocatalysts in CV and PEMFC. However, PEMFC performance showed that the synthesized ORR electrocatalyst Pt-Ni(3:1)/CAB-EG is better than Pt-Co(3:1)/CAB-EG. The Pt-Ni(3:1)/CAB-EG in PEMFC at optimum cell conditions i.e., electrocatalyst loading at anode 1 mg/cm 2 and cathode 1 mg/cm2, flow rate of anode/cathode species of 50/60 ml and cell temperature of 60 oC produced Indian Institute of Technology (BHU), Varanasi xxiv Preface a maximum power density of 42.29 mW/cm2 at a current density of 102.4 mA/cm2 with an OCV of 0.908 V. The statistical analysis response surface methodology (RSM) was also used to developed a mathematical model and validate the same with experimental data. The optimum condition optimized through the RSM was very close to the experimental result. The % errors of power density between predicted and experimental value at optimum condition was found 0.31 % which is in permissible limit. The subject matter contained in the thesis has been arranged in six different chapters. In the Chapter 1, an overview was given about the energy demand and supply in present scenario, overview of fuel cell and its development along with its advantages over the other types of energy sources and use of hydrogen as fuel in the fuel cell for energy applications. At the end of the chapter, discussion about cathode electrocatalyst, synthesis of the cathode electrocatalyst using various non polar and polar solvents along with their advantages and disadvantages are described. Chapter 2 explains the advancement of PEMFC from its inception along with describing the main components of PEMFC i.e., membrane electrolyte, electrocatalyst used as anode and cathode, gas diffusion layer along with the physical and chemical characterization techniques of electrocatalyst. This chapter also includes details about literature review of cathode electrocatalyst for PEMFC, PEMFC performance comparison about different types of cathode electrocatalyst. At the end of the chapter 2, objectives of the present thesis work is discussed. Chapter 3 covers the material used in the experiment along with their experimental specifications for the synthesis of cathode electrocatalyst. The fabrication of working cathode electrode for half-cell and preparation of anode, cathode and forming a membrane electrode assembly (MEA) for the evaluation of PEMFC performance in a single cell setup are discussed in this chapter 3. Chapter 4 covers the optimization of the PEMFC performance by considering the synthesized cathode electrocatalyst loading as the factor along with cell temperature and hydrogen Indian Institute of Technology (BHU), Varanasi xxv Preface flow rate as other factors for maximizing the power density of the PEMFC by using box behnken design model. Chapter 5 covers the results and discussion which provides discussion about the physical characterization of the synthesized cathode electrocatalyst types, chemical characterization of the cathode electrocatalyst including cyclic voltammetry and electrochemical impedance spectroscopy and various findings interpreted from the characterization techniques. The performance of PEMFC using synthesized cathode electrocatalyst types is also discussed in this chapter. Chapter 6 concludes the findings and discussion about the present work along with suggestions. At the end of the thesis, future scope of present research work, references and appendices are provided. Indian Institute of Technology (BHU), Varanasi xxvi Chapter 1 Introduction CHAPTER - 1 INTRODUCTION The energy demand has recently increased considerably due to increased population around the world. The energy demands in the various sectors like domestic, industrial and automobiles are fulfilled by traditional/conventional energy resources like energies such as crude oil, coal, natural gas, and so on (Choudhary and Pramanik 2020a; Singh and Pramanik 2012). Thus, consumption rate of conventional energy resources have gone up tremendously. However, the limited supply of conventional energy resources e.g., crude oil, coal and natural gas along with pollution problem are the main reason to think over alternative energy resources. The energy infrastructure is a vital component for a country’s economy and economic growth. In general, two forms of energy, (i) thermal energy and (ii) electrical energy, are widely employed around the world. The creation of necessary electrical infrastructure is critical to the Indian economy in long-term prosperity. The energy demand is rising in together with economic activity. The energy demand of India is increased by roughly 4.1% over the last decade, and it is expected to climb by 6% per year over the next decade (CEA, 2022). To accommodate the rising demand for electricity, the power sector of India has expanded significantly. According to the central electricity authority (CEA, 2022), the government of India, coal is used in the highest amount for electricity generation (51 %), followed by natural gas (6 %), petroleum (0.0012 %), renewable energy (39 %), lignite (2 %) and nuclear energy (2 %). The total installed capacity of renewable electrical energy is made up of small hydro plants (3 %), bio-Power (7 %), wind (26 %), solar (34 %), and large hydro plants (30 %). As alternative the energy demand in the domestic and industrial sectors are met by conventional energy resources like, crude oil, coal, natural gas etc. However, the availability of fossil fuels (coal, Indian institute of Technology IIT (BHU), Varanasi Page | 1 Chapter 1 Introduction natural gas, petroleum and nuclear energy) are limited, and they are also the main cause to air pollution by emitting harmful pollutant gases like CO2, SOx, and NOx. The burning of fossil fuels are also responsible for global warming because emission of CO2 and other gases (chlorofluorocarbons), which caused the heat-trapping in environment due to this earth temperature gradually increases with time. In nuclear energy production accidental leakage of radioactive rays is one of the main danger to human life, while transportation of nuclear fuel to a nuclear power plant can cause pollution to environment. It was found that nonrenewable energies are very costly and its use is also harmful for human health as well as environment. Renewable energy sources have a lot of advantages, but there are also certain drawbacks that need to be taken into account. The fluctuating supply of renewable energy is a serious disadvantage. When compared to wind power, which depends on wind speed, solar power depends on sunlight availability. It may be difficult to regularly match supply and demand because of this random nature. Batteries and various other energy storage technologies are being developed to address this problem, but they are currently very expensive and have capacity restrictions. Most renewable energy systems need considerable investments in land and resources. Large-scale wind and solar farms need a lot of land, which raises the cost of initial installation. Hydropower is one of several renewable energy sources that can have an impact on rivers and aquatic ecosystems. The initial cost of installing infrastructure for renewable energy sources can still be rather substantial. The main problem with biomass is its high moisture content, which complicates both pre-treatment and conversion procedures. When compared to traditional fossil fuels, renewable energy sources like wind and solar have substantially lower energy densities. Solar panels and wind turbines are two examples of renewable energy technologies that are produced through the extraction of raw materials and manufacturing procedures that may have an adverse effect on the environment. Indian institute of Technology IIT (BHU), Varanasi Page | 2 Chapter 1 Introduction Additionally, certain parts of outdated or damaged equipment include dangerous compounds that need to be handled carefully and recycled, making disposal a task. It can be necessary to improve and modify current infrastructure significantly in order to integrate renewable energy into power systems. Due to the intermittent nature of renewable energy sources, a strong and adaptable grid system that can manage, the changes in supply and demand is necessary. These improvements might be time and money consuming. The overall amount of renewable energy from wind, water, and the sun will continue to rise, but due to their irregular availability, these sources are unsuitable for supplying the electrical energy base requirement. However, the main reason to consider alternative energy-producing technologies like fuel cells is the limited supply of conventional energy supplies, such as crude oil and coal, and the inconsistent availability of renewable energy. A fuel cell directly transforms the chemical energy of a fuel into electrical energy. Fuel cells are silent, portable and a source of clean energy. Hydrogen fuel-based fuel cell don't emit any harmful pollutants like SOX and NOX. As a result of their high theoretical efficiency and low level of pollution, fuel cells have been gaining attention (Pramanik and Rathoure 2017). The development of fuel cells as energy conversion devices began in the middle of the 19th century in 1839 (Bossel 2000; Larminie and Dicks 2003). Sir William Grove developed the fuel cells as an electrical energy conversion technology, however Christian Friedrich Schonbein actually found the basic idea (Carrette et al., 2001). The fuel cells are one of the oldest electrical energy conversion technologies known to man. As a result of the growing popularity of electricity at the beginning of the twentieth century, the conversion of chemical energy into electrical energy became more significant. The electrical energy conversion systems were first presented as small dispersed power generators, but subsequent advances resulted in megawatt-scale centralized plants. The need to enhance the flexibility of electricity generating, as well as the increase in population of world, have led to a Indian institute of Technology IIT (BHU), Varanasi Page | 3 Chapter 1 Introduction growing interest in the creation of more powerful and more evenly distributed power generation during the previous decade. Fuel cells use pure hydrogen to generate electricity and only produce water as a byproduct, reducing our dependence on fossil fuels and preventing the release of any harmful gases. The free energy of a chemical process is turned into electrical energy through a fuel cells, which are galvanic cells. The cell voltage and a chemical reaction's change in Gibbs free energy. The cell voltage and the Gibbs free energy change of a chemical reaction are connected via Equation 1.1. ΔG = - nFE0 (1.1) Where E0 is the voltage of the cell for thermodynamic equilibrium in the absence of a current flow, n is the number of electrons involved in the reaction, F is the Faraday’s charge constant. A fuel cell consists of two electrodes sandwiched around an electrolyte. The oxidant oxygen passes over one electrode (cathode) and hydrogen or hydrogen rich molecule fuels over the other electrode (anode), generating electricity, water and heat as shown in Figure 1.1. The hydrogen gas ionizes at the anode of fuel cell, releasing electrons and producing H + ions (Equation 1.2). Water is formed when oxygen combines with electrons and H+ ions from the electrolyte at the cathode (equation 1.3). It is clear that in order to continue these reactions (Equation 1.1 to Equation 1.2), the electrons created at the anode must travel to the cathode via an electrical circuit. The electrolyte must also permit the passage of H+ ions from anode to cathode. Anode Reaction: 2H → 4H + 4e (1.2) Cathode Reaction: O + 4e + 4H → 2H O (1.3) Indian institute of Technology IIT (BHU), Varanasi Page | 4 Chapter 1 Introduction Figure 1.1 Hydrogen/oxygen fuel cell and its reactions based on the proton exchange membrane. The anode and cathode electrodes, as well as an electrolyte, are present in every fuel cell. Different electrolytes and electrodes are used in fuel cells, and different temperatures are used for different electrochemical processes. Because of this, each type of fuel cell (or fuel cell technology) has unique advantages and disadvantages, and making it better suited for particular markets and applications. The hydrogen fuel-based low temperature fuel cells gaining attention due to their flexibility to choose electrolyte material like Nafion ® as proton exchange membrane (PEM), alkaline solution KOH and phosphoric acid, etc (Choi et al., 2021). The proton exchange membrane fuel cells (PEMFC) are mostly used as a source of energy for a wide range of commercial or industrial applications (Rodriguez et al., 2021; shroti and Daletou 2022). The low temperature fuel cell has high power at relatively low temperatures of 30-100 oC in comparison to Indian institute of Technology IIT (BHU), Varanasi Page | 5 Chapter 1 Introduction other types without emitting any harmful emissions. High energy density and low operating temperature make the PEMFC more reliable for future energy requirements over fossil fuel-based energy devices. Moreover, fossil fuels storage is limited and they are gradually decreasing as the energy demand is increasing day by day. The hydrogen based PEMFC is considered as an alternative to fossil fuels for future energy generation (Rodriguez et al., 2021). The PEMFC is similar to any sort of battery in which anode, cathode and electrolyte/PEM form a sandwich having electrolyte in between anode and cathode (Termpornvithit et al., 2012). The fuel hydrogen is fed at the anode and oxidant oxygen/air at the cathode irrespective of the type of electrolyte used in various types of low temperature fuel cells. However, fuel cells suffer from different types of losses/polarization viz activation losses, ohmic losses and concentration losses. Activation polarization is due to the slow electrochemical reactions at the electrode surface, where the species are oxidized or reduced in a fuel cell electrode reaction. Activation polarization is directly related to the rate at which the fuel or the oxidant is oxidized or reduced (Tayal et al., 2012). This loss in potential, switch over the fuel cell reaction reversible to irreversible and it predominates at the start of fuel cell. The origin of ohmic polarization comes from the resistance to the flow of ions in the electrolyte and flow of electrons through the electrodes and the external electrical circuit (Srinivasan 2006). The concentration losses occur over the entire range of current density. However, these losses become prominent at high limiting currents where it becomes difficult for gas reactant flow to reach the fuel cell reaction sites. Several factors are responsible for the concentration polarization. The main reason for concentration polarization is the resistance to the mass transfer from outer surface (bulk) of gas diffusion layer (GDL) to electrocatalyst sites and it predominates at high current density. Among, Indian institute of Technology IIT (BHU), Varanasi Page | 6 Chapter 1 Introduction these three types of major polarization in fuel cells, activation loss is the important one. As, literature suggest that faster electrode kinetics of fuel cell improves current density which in return gives high power density at low activation loss. Thus, fabrication of fuel cell electrode and its micro structure is an important aspect. The performance of electrode could be enhanced by synthesizing a suitable bimetallic alloy electrocatalyst. It is seen in literature that the cathode activation loss is higher than the anode activation loss for low temperature fuel cell in acidic medium. It is well known through various studies reported in the literature that anode electrooxidation of H2 fuel in presence of Pt based electrocatalyst is faster in acidic medium/PEM in comparison to oxygen reduction at the cathode (Wang et al., 2008). Thus, slow reduction kinetics at cathode on single metal Pt-based electrocatalyst for PEMFC is one of the many challenges like proton conductivity problem at elevated temperature (T) > 80 oC, high activation loss and high cost of pure Pt-based electrocatalyst. The oxygen reduction at the cathode of a PEMFC proceeds through either 2 step 4 electron mechanism (Equation 1.4 to Equation 1.7) or a single step 4 electron mechanism as is given below Equation (1.8). O + Pt → Pt − O (1.4) Pt − O + H + e → Pt − HO (1.5) Pt − HO + Pt → Pt − OH + Pt − O (1.6) Pt − OH + Pt − O + 3H + 3e → 2Pt + 2H O (1.7) Or O + 4H + 4e → 2H O (1.8) Indian institute of Technology IIT (BHU), Varanasi Page | 7 Chapter 1 Introduction The ORR mechanism via 2 steps 4 electron path indicates that chemisorption of oxygen takes place in the first step (Equation 1.5) which further proceeds and at the end, only water molecule is produced as a byproduct on the cathode (Equation 1.7) (Bard et al., 2022; Arico et al., 2001; Xiong et al., 2018). Apart from slow reduction kinetics at the cathode of a PEMFC, activation loss also contributes to voltage loss when current is drawn from the cell (i > 0). Thus, developing an efficient cathode electrocatalyst could positively improve cell performance in term of voltage and current density. Till date noble metal Pt-based electrocatalyst is widely used at fuel cell cathode for ORR (Pramanik et al., 2017). Presently, researchers are working tremendously to develop a highly efficient bimetallic cathode electrocatalyst that could reduce the consumption of expensive platinum (Pt), reduce activation loss/overpotential, and improves current density to a few fold higher than the existing one. All these improvements intern would give higher power output from a single PEMFC or stack at a low cost. The cost of a fuel cell depends on the individual cell components like anode electrocatalyst, cathode electrocatalyst, membrane electrolyte, gas diffusion layers, and current collectors/flow channels. Thus, reduction of cathode electrocatalyst cost by adding other non-noble metals Co, Ni, Cr, and W to Pt when developing bimetallic electrocatalysts for oxygen reduction reaction (ORR) at PEMFC cathode, would undoubtedly reduce the total fabrication cost of the fuel cell. Most of the published literature shows that noble metals like Pt, Pd, and Ru are considered as suitable electrocatalyst for ORR at the cathode side of a low temperature fuel cells (Rodriguez et al., 2021; Shroti and Daletou 2022; Termpornvithit et al; Balbuena et al., 2012; Chaisubanan et al., 2015). The cathodic properties of noble metals mainly depend upon their crystallite size, shape, and electronic configuration. The catalytic activity of Pt is the best among all noble metals which are often used in ORR of a low temperature PEMFC. The electrocatalytic performance of Pt based Indian institute of Technology IIT (BHU), Varanasi Page | 8 Chapter 1 Introduction nano-crystals strictly depends upon their morphology due to the exposed surface which has distinct crystallite planes according to their size and shapes (Guo et al., 2013; Chen et al., 2009; Peng and Yang 2009). Antolini et al., (2005) reported that the activity of electrocatalysts supported by Pt alloy is increased when Pt-Pt bond distance got decreased. Paffett et al., (1988) reported the dissolution of more oxidizable Pt alloying and its change in surface structure improve the activity of Pt based ORR electrocatalysts. Thus, many such works on the synthesis of bimetallic alloy electrocatalysts like Pi-Co, Pt-Ni, Pt-Cr, have been reported in the open literature. Peng et al., (2009) explained that the addition of a transition metal to Pt not only enhanced kinetics but also provided the electrocatalyst with the proper crystallite phase and composition, allowing for optimal atomic arrangements. Although various efforts have been made to synthesize suitable Pt based bimetallic electrocatalysts, the effect of various types of solvents has never been studied earlier for catalyst synthesis in any research works. It should be noted that solvent also plays a key role in synthesizing highly active electrocatalysts by acting as an agent in the preparation of highly active core-shell electrocatalysts and controlling the size of synthesized particles and shape as well. The reaction equilibrium, reaction kinetics, and products all could be significantly altered by the interactions of solvents with reactants, intermediates, and products. The interaction of solvents with nanoparticles or their decomposition products can function as structural modulators. The solvent effects are influenced by the solvent's polarity, dielectric constants, and viscosity (Demazeau 2010). The compatibility of dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), ethylene glycol (EG) and water (W) with common reactants has led to their frequent usage as solvents. The main purpose of present study is to find out the best solvent for synthesis of most active and efficient cathode electrocatalysts which could enhance the performance of a PEMFC. Thus, the commonly used Indian institute of Technology IIT (BHU), Varanasi Page | 9 Chapter 1 Introduction solvents as referred in the various literatures were selected as solvents in the present study. It should be noted that there is no such research work on comparative study on solvents for electrocatalyst synthesis. Most of the research work used single solvent like EG or DMSO or DMF or water as solvent for the electrocatalyst synthesis in their study (Khan et al., 2022; Chen et al., 2017a; Chaudhary and Pramanik 2022). It is very difficult to compare the effect of solvents in electrocatalysts synthesis by comparing the performance of electrocatalyst reported in various reported published literature, as the synthesis method or metals types or electrocatalysts supports always differ from each other in the reported research works. Thus, undoubtedly this present research work will enable to understand the effect of various solvents in bimetallic Pt-M cathode electrocatalyst synthesis for same catalyst support, metal composition with same concentration in all the four synthesized electrocatalysts. Moreover, the merits and demerits of the proposed solvents are also important factors before it is used for catalysts synthesis. It is seen from the thorough literature survey that EG has several important properties over other solvents such like DMSO and DMF and water. It is fact that EG is less expensive and less harmful than other organic solvents. The EG has also been used extensively as a solvent and reducing agent, since it contains hydroxyl groups with reducing properties (Lai et al., 2015b). The several important properties of EG facilitates the formation of electrocatalysts of better quality. The other three solvents DMSO, DMF and water have some merit and demerits. The DMSO is often utilised as a solvent in the production of numerous organic and inorganic compounds (Tashrifi et al., 2020) However, a major problem of DMSO is strong pungent odour which causes nausea. Similarly, the DMF is an organic solvent with a broad solubility range for both organic and inorganic molecules and may be used as an alternative solvent (Lai et al., 2015b). The demerits of DMF is fishy or ammonia like odour, hazardous in nature, long-term exposure may damage the liver, kidneys and causes headache, Indian institute of Technology IIT (BHU), Varanasi Page | 10 Chapter 1 Introduction dizziness. Water (W) as solvent provides many benefits e.g., with increase in temperature - (i) ion product increases (ii) viscosity decreases, high polarity, natural resource so easily available therefore cheap in cost (Lai et al., 2015b and Demazeau 2010). The demerits of water is high critical point, lower yield of water insoluble bio-oil. In contrary, EG has no any harmful effect on human health for handing, no odour problem and not even hazardous in nature. Thus, EG could be preferred as solvent over DMSO, DMF, and W, respectively. To recommend ethylene glycol (EG) as best solvent, a thorough studies is required, however, no such detailed studies on the synthesis of cathode electrocatalysts using various types of solvents and thorough characterization of the synthesized electrocatalysts followed by testing in half-cell and single cell PEMFC have been reported to date. In this perspective, bimetallic Pt-M/C AB (M = Co, Ni) electrocatalysts were synthesized in the laboratory using various types of solvents for effective ORR in hydrogen based PEMFC. Four different types of solvents namely dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), ethylene glycol (EG) and water (W) were used for the synthesis of three different types of bimetallic cathode electrocatalysts e.g., Pt-Co/C AB-DMSO, Pt-Co/CAB-DMF, Pt- Co/CAB-EG and Pt-Co/CAB-W via solvothermal process maintaining the synthesizing temperature very close to their boiling temperature. Among all four solvents, ethylene glycol (EG) based solvothermal process produced highly efficient active cathode electrocatalyst Pt-Co/C AB-EG which exhibited the best performance for ORR in half-cell and single PEMFC. In the chapter 1, the present energy generation scenario and its disadvantages with alternative sources to meet the current requirements using PEMFC technology are comprehensively examined. Chapter 2 discussed a thorough literature review including membrane electrolyte, electrode materials, different characterization techniques of cathode electrocatalyst, performance of a single PEMFC with different type of cathode electrocatalysts, and in the end thesis objectives Indian institute of Technology IIT (BHU), Varanasi Page | 11 Chapter 1 Introduction on the basis of detailed literature review. Chapter 3 provides information on the materials used in the experiment as well as experimental details to perform proton exchange membrane fuel cell based on hydrogen fuel, the synthesis of cathode electrocatalyst, the physical and electrochemical characterization of synthesized electrocatalyst, the fabrication of electrodes, and single cell performance. In Chapter 4, the response surface methodology was discussed to optimized operating parameters of the PEMFC to obtain maximum power density. The results and discussion in Chapter 5 are based on the physical characterization of the synthesized cathode electrocatalyst using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM), while electrochemical characterization was carried out using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Using polarization and power density curves, the outcomes of single PEMFC investigations are discussed. Using RSM, process parameters are optimized, and the outcomes are thoroughly examined with experimental results at optimum and random condition of process parameters, and stability test also discussed in the end of this chapter. Finally, Chapter 6 provides a summary of the thesis with key findings and conclusion as well as some significant suggestions for additional research in this field. At the end of thesis references and appendices are presented. Indian institute of Technology IIT (BHU), Varanasi Page | 12 Chapter 2 Literature review and objectives CHAPTER 2 LITERATURE REVIEW AND OBJECTIVES The detailed literature review on hydrogen-based proton exchange membrane fuel cells for development to provide low cost power has led to the identification of significant research gaps and based on the most significant research gaps after thorough literature review, the objectives are discussed in this chapter. The working principles of proton exchange membrane fuel cells (PEMFC), main components of PEMFC, characterization of cathode electrode electrocatalysts, and the performance of a hydrogen based PEMFC are thereby discussed in this chapter. 2.1 Proton exchange membrane fuel cell advancement The polymer electrolyte membrane (PEM) fuel cell, often referred to as a proton exchange membrane fuel cell (PEMFC), is a kind of fuel cell that is primarily being developed for transportation purposes, as well as for stationary fuel cell applications and portable fuel cell applications. The proton exchange membrane fuel cell (PEMFC), also known as the solid polymer fuel cell (SPFC), was invented in the 1960 by General Electric for use in first manned space vehicles mission of national aeronautics and space administration, America (Larminie and Dicks 2003). A unique proton conduction polymer electrolyte membrane and lower temperature range (30 to 100 °C) is its distinctive characteristics for the electricity production by PEMFCs. The membrane electrode assembly (MEA) that include electrodes, an electrolyte, an electrocatalyst, and a gas diffusion layer are the foundation of PEMFC construction. The electrolyte is an ion conduction polymer to which an electrocatalytic porous electrode is attached on each side. The anode-electrolyte-cathode assembly is thus a single unit and extremely thin. These membrane Indian institute of Technology IIT (BHU), Varanasi Page | 13 Chapter 2 Literature review and objectives electrode assemblies (MEA) are commonly connected in series using a bipolar plate. The mobile ion in the polymers utilized is an H+ ion or proton, the basic operation of the cell is significant the same as that of an acid electrolyte fuel cell (Choudhary and Pramanik 2020a). The polymer electrolytes work at low temperatures, a PEMFC can start rapidly, because the MEA is thin, so that compact nature of fuel cells can be created (Singh and Pramanik 2022). There are no hazardous fluid dangers, and the cell can operate in any location. As a result, the PEMFC is ideal for usage in automobiles and portable applications (Carrette et al., 2001). Early versions of the PEMFC, like as those used in Gemini spacecraft of NASA, had a small lifespan of some hours, but it was sufficient for those early missions. It was decided not to pursue the commercial development of the PEMFC due to the high cost compared to other fuel cells, such as the phosphoric acid fuel cell that was then being developed, as well as the problem of water management in the electrolyte, which was too challenging to manage reliably. The development program was carried on with the inclusion of a new polymer membrane like, nafion was a registered brand of Dupont in 1967. These membranes are much more stable than polystyrene sulfonate membranes and have higher conductivity and acidity. A polytetrafluoroethylene (PTFE) based structure makes up the Nafion, which is chemically inert in both reducing and oxidizing conditions. The equivalent weight, which is inversely correlated to the ion-exchange capacity and is defined as the weight of polymer that will neutralize one equivalent of base, is the distinguishing property of proton conducting polymer membranes. The advancements made in recent years have increased density significantly while simultaneously reducing the consumption of platinum (Maiti et al., 2022). These advancements have resulted in a significant decrease in cost per kilowatt of power and enormous rise in power density. The PEMFCs are actively being developed for use in automobiles and public transportation vehicles, as well as for a huge variety of portable applications (Chen and Indian institute of Technology IIT (BHU), Varanasi Page | 14 Chapter 2 Literature review and objectives Laghrouche 2021; Lou et al., 2021). It might be argued that PEMFCs have more potential uses than any other electrical energy generation technology. In view of this, for the last two decades, researchers across the world are involved in the research and development actively for the manufacturing of low cost fuel cell components like anode electrocatalyst (Ke et al., 2022), cathode electrocatalyst (Polagani et al., 2024), proton exchange membrane (Jiang et al., 2021), and GDL (Athanasaki et al., 2023). In the present thesis, development of cathode electrocatalyst using non noble metal with Platinum (Pt) is considered to enhance the oxygen reduction reaction kinetics of cathode. 2.1.1 Main components of proton exchange membrane fuel cell (PEMFC) The anode and cathode electrodes, electrolyte, fuel, and oxidant compose the components of the proton exchange membrane fuel cell. The electrocatalyst is the main functioning part of the anode and cathode electrode. The polymeric solid proton exchange membrane is used as electrolyte keeping in between anode and cathode electrode, and further hot pressed/clamped to use the assembly as MEA in PEMFC. Fuel and oxidant are supplied through anode and cathode side. The next subsections, various components like electrolyte, anode and cathode electrocatalyst materials, electrooxidation of hydrogen and oxygen reduction reactions are discussed. 2.1.1.1 Membrane electrolyte Although Nafion® is the widely studied and used electrolyte for PEM based fuel cells, additional perfluorocarbon sulfonic acid membranes from Dow, Gore, and Asahi Chemical are also used and studied (Singh and Pramanik 2022; Wakizoe et al., 1995; Yeager and Steck 1981). Membranes typically have a narrow temperature range typically (30 oC to 100 oC) over which they are stable. The maximum temperature limit is determined by the retention rate of water by the membrane Indian institute of Technology IIT (BHU), Varanasi Page | 15 Chapter 2 Literature review and objectives humidification, as water is exhibited for H+ ion conduction through membrane electrolyte. However, the manufacturing of composite membrane improves membrane structure and conductivity. This can be accomplished in a variety of methods, one of which is to reinforce the perfluorosulfonic membrane with PTFE components, as Gore and Asahi Chemicals have done successfully (Wakizoe et al., 1995 and Liu et al., 2024). Another option is to saturate a membrane with a solution or a solid in order to reduce the permeability of the reactant gases (Peighambardoust et al., 2024). Another method is to dissolve the membrane in a suitable solvent and mix it with another substance (Figoli et al., 2014). The composite membrane can be employed in a fuel cell, after it has been recast (Broka and Ekdunge 1997 and Pu et al., 2014). To develop thinner membranes and reduce membrane resistance in the system, PTFE sheets were also impregnated with Nafion ionomer (18 wt. % Nafion® in EtOH) (Nouel and Fedkiw 1998). This membrane has a conductivity comparable to Nafion® 112 (0.1 Scm-1) but a higher permeability to gases. The Polyvinylidene fluoride (PVDF) sheets grafted with radiation produced membranes with lower oxygen solubility but higher diffusion than Nafion membranes (Sadeghi et al., 2018). As long as these membranes are physically and electrochemically stable, they hold potential for PEM fuel cells. Recently, Goo et al., 2020, Zhang et al., 2019 and Ye et al., 2011 develop proton exchange membrane for hydrogen-based fuel cell application. The membrane electrolyte developed by Goo et al., 2020 using sulfonated hydrocarbon-based polymer to synthesized nafion composite membranes through coating and blending. The membrane was characterized by electrochemical impedance spectroscopy (EIS) to determine ionic conductivity. The conductivity was found in the range of 223.3 mScm-1 (80 oC). However, the membrane has anisotropic swelling and dimensional instability problem. Similarly, Ye et al., 2011 synthesized nafion-titania nanocomposite membranes using an in situ sol-gel method by hydrolyzing and condensing precursors using nafion Indian institute of Technology IIT (BHU), Varanasi Page | 16 Chapter 2 Literature review and objectives solution. The proton conductivity of this electrolyte membrane is of the order 5x10 -3 Scm-1 (100 o C). In Present study Nafion® 117 is used as electrolyte membrane for proton exchange membrane fuel cell due to its excellent mechanical, thermal, and chemical activity. Apart from this the ionic conductivity of Nafion® 117 is also very high (Choudhary and Pramanik 2019). 2.1.1.2 Electrodes To ensure that reactant gases are supplied to the active zones where the noble metal electrocatalyst is in good contact with the ionic and electronic conductor, PEM fuel cell electrodes are made typically porous for gas diffusion. It takes careful preparation and attention to create gas diffusion assembly (GDA), and each step of the process is crucial. It is well known that an electrode must have a three-phase boundary (Choudhary and Pramanik 2019) between the reactants (fuel/oxidant) supply, the electrocatalyst particle, and the ionic conductor on one side i.e., membrane electrolyte. To ensure that electrons are delivered to or removed from the reaction site, the particles must come into direct contact with an electronic conductor (Figure 2.1). The electrocatalyst particles are often supported on a carbon substrate, which typically provides electronic conductivity. The anode and cathode electrode are generally prepared from the electrocatalyst, activated carbon and mixture of Nafion® ionomer and PTFE dispersion, which acted as binders. The PTFE, along with pores, provide a flow network which allows easy escape of the reaction products from electrode surface. Typically, GDL for electrode preparation uses Toray carbon paper or carbon cloths. The electrocatalyst layer is covered with an ionomeric binder i.e., Nafion ® solution before the electrode is pressed or clumped against the membrane to create the three-phase assembly. Thus, the majority of electrocatalyst particles will have good ionic interaction with the ionomer material covering the membrane. When utilizing humidified gases the electrocatalyst layer must be Indian institute of Technology IIT (BHU), Varanasi Page | 17 Chapter 2 Literature review and objectives hydrophobic enough to keep the pores from flooding. This hydrophobicity can be achieved by combining hydrophobic PTFE as a binder with hydrophilic Nafion ®. The choice of electrocatalyst based on fuel, oxidant, and electrolyte medium, affects the performance of PEMFC. The most active and efficient part of an electrode is the electrocatalyst, which actively participate in the electrooxidation at the anode and reduction processes at the cathode of the cell. There are various types of electrocatalysts that have been used so far for anode and cathode fabrication of a hydrogen based PEMFC. (Ramli et al., 2024; Etesami et al., 2022 and Zhang et al., 2021). The anode and cathode electrocatalyst are discussed in the subsequent section. Figure 2.1 Three phase network formed by electrocatalyst particles, inomer and gas phase in a porous structure, ensuring both electronic and ionic contact as well as gas transport. 2.1.1.3 Anode electrocatalyst material The anode performs well when pure hydrogen is utilized as fuel with pure Pt catalyzing the electrooxidation of hydrogen (Fan et al., 2022; Seo et al., 2020; Tzorbatzoglou et al., 2018 and Durst et al., 2014). However, in most fuel cells, which use other fuel stream like, ethanol methanol, glycerol etc, the electrooxidation become very difficult on pure Pt electrocatalyst due to the Indian institute of Technology IIT (BHU), Varanasi Page | 18 Chapter 2 Literature review and objectives complex molecular structure of these alcohols (Ke et al., 2022; Choudhary and Pramanik 2020b; Gupta and Pramanik 2019 and Ball et al., 2007). All of these above substances have the potential to deactivate the anode electrocatalysts to varying degrees due to formation of some complex. The low-temperature fuel cells based on hydrogen fuel also suffers from CO poisoning of the Pt electrocatalyst if hydrogen fuel contains CO or impurities (Dubau et al., 2014 and Oetjen et al., 1996). The CO poisoning occurs in PEMFC due to the adsorption of the CO species to the active sites of the platinum electrocatalysts, resulting in no, or almost no, sites available for reaction with H2 (Molochas and Tsiakaras 2021). The performance of the anode reaction is determined by (i) the interaction between the electrocatalyst surface and the fuel hydrogen, (ii) formation of absorbed species and interaction with the electrocatalyst surface (Equation 2.1), and (iii) formation of H + ions and electrons (Equation 2.2). Since the kinetics of electrooxidation on Pt electrocatalyst is extremely fast. As already mentioned on Pt-based electrocatalysts, the electrooxidation of hydrogen occurs easily. In a PEMFC, the oxidation of hydrogen at higher current densities is usually restricted by mass-transfer from bulk phase to active electrocatalyst sites. Further, the adsorption of the hydrogen gas onto the electrocatalyst surface, followed by the dissociation of hydrogen and an electrochemical reaction that produces two hydrogen ions, are important reaction steps in the oxidation of hydrogen occurs as following (Equation 2.1 to 2.3) (Lei et al., 2019; Wang et al., 2009 and Carrette et al., 2001). 2Pt ( ) + H → Pt − H + Pt − H (2.1) 2(Pt − H ) → 2H + 2e + 2Pt ( ) (2.2) Where Pt-Hads is an adsorbed H-atom on the Pt active site and Pt (s) is a free surface site. Indian institute of Technology IIT (BHU), Varanasi Page | 19 Chapter 2 Literature review and objectives The overall result of hydrogen oxidation is: H → 2H + 2e (2.3) It is well known that in proton exchange membrane fuel (PEMFC), Pt/C is the most often used as anode active electrocatalyst material (sun et al., 2022; Singh and Pramanik 2022; Shroti and Daletou 2022; Ohyagi and Sasaki 2013; Termpornvithit et al., 2012 and Iyuke et al., 2003). The noble metal Pt is very expensive also is not available easily (Singh and Pramanik 2024). Many researchers have been focusing on developing Pt-alloyed Pt-X (where X = Mo, W etc) electrocatalysts to reduce the excessive use of expensive Pt electrocatalyst (Ke et al., 2022 and Serov and Kwak 2009). Molochas and Tsiakaras (2021) found that when Pt alloyed with Mo and W, the sufficient incorporation of Mo and W with Pt ensure adequate stability of PEMFC for longer duration as well as enhance the CO tolerance through bifunctional characteristics of Mo and W. Although, some bimetallic electrocatalyst have been developed for electrooxidation of hydrogen, the performance of PEMFC in terms of power density is not promising. Thus, in the current research work, commercial Pt/C (40 wt. %) was chosen as the anode electrocatalyst. To get higher PEMFC performance, the cathode electrocatalyst must be selected as carefully that of anode electrocatalyst. The cathode electrocatalyst is discussed in the next section. 2.1.1.4 Cathode electrocatalyst material There are many cathode electrocatalyst for oxygen reduction reaction (ORR) available such as pure Pd, Pt, Rh, Ir metal and its metal-alloy etc (Ramli et al., 2024 and Antolini 2014). The electrocatalytic activity of Pt towards ORR strongly depends on its O 2 adsorption energy, the dissociation energy of the O-O bond, and the binding energy of OH on the Pt surface. The electronic structure of the Pt catalyst (Pt d-band vacancy) and the Pt-Pt inter-atomic distance Indian institute of Technology IIT (BHU), Varanasi Page | 20 Chapter 2 Literature review and objectives (geometric effect) can strongly affect these energies (Stassi et al., 2006). Theoretical calculations on O2 and OH binding energy for several metals had predicted that Pt should have the highest electrocatalytic activity among other metals with the ORR activity of Pt > Pd > Ir > Rh (Norskov et al., 2004). The activity of electrocatalyst enhancement occurs when Pt is alloyed with other metals that can be explained by the change in electronic structure i.e., the increased Pt d-band vacancy and in geometric effect i.e., Pt-Pt inter-atomic distance). Alloying of other metals like Co, Ni, Cu etc with Pt causes a lattice contraction, leading to a more favorable Pt-Pt distance for the dissociative adsorption of O2 (Singh and Pramanik 2022; Antolini et al., 2005). Till date, Pt catalysts have the broad applications in fuel cells for their high catalytic activity and long durability (Singh and Pramanik 2022; Zhang et al., 2020; Lai et al., 2015a; Wang et al., 2014; Demazeau et al., 2010 and Iyuke et al., 2003 ). However, using pure Pt as electrocatalyst supported on high surface area carbon powder as support material is very costly and not economical. So instead of pure Pt/C electrocatalyst, the idea of Pt-based bimetallic alloys has been used widely for the oxygen reduction reaction studies, due to their high activity and excellent stability in acidic medium. It is possible to alloy Pt with transition metal (M) (where, M = Co, Ni, Cu and Pd) to minimize the content of Pt as well as cost of electrocatalyst and improve the electrocatalytic performance. The synthesized electrocatalyst could reduce the surface adsorption of the products and/or intermediated species, causing the increase in the active sites accessible for fresh reactants (Zhang et al., 2021; Kulkarni et al., 2018; Wang et al., 2015b; Zheng et al., 2014; Jayasayee et al., 2012 and Jang et al., 2011). The laboratory based synthesized Pt-based bimetallic alloys provides abundant active sites, ordered structures and Pt-rich surfaces as compared to commercial costly Pt/C electrocatalyst (Zhang et al., 2019; Wang et al., 2018b; Xia et al., 2015 and Zhang et al., 2003). Recently, several studies on the oxygen reduction reaction, using Pt-based bimetallic Indian institute of Technology IIT (BHU), Varanasi Page | 21 Chapter 2 Literature review and objectives electrocatalysts like Pt-Co (Sun et al., 2022; Singh and Pramanik 2022; Sneed et al., 2018; Deshpande et al., 2016; Yang et al., 2016 and Guo et al., 2013), Pt-Ni (Tian et al., 2019; Gong et al., 2019; Lin et al., 2018; Shen et al., 2015a; Zhang et al., 2010; Lia et al., 2015 and Stamenkovic et al., 2007) and Pt-Fe (Wang et al., 2018a; Wang et al., 2015 and Shui et al., 2001), Pt-Cu (Zhou and Zhang 2015; Liu et al., 2014), Pt-Pd (Liu et al., 2012; Lee et al., 2012 and Zhang et al., 2012) have been studied. Apart from bimetallic electrocatalyst, trimetallic electrocatalyst via Pt-Co-Fe (Yang et al., 2023), Pt-Ni-Cu (Liu et al., 2014), Pt-Cu-Ag (Zhou and Zhang 2015), Pt-Pd-Cu (An et al., 2018), and Pt-Pd-Au (Lankiang et al., 2015) have also been tested. The performance reported by the trimetallic electrocatalyst for ORR is not promising to that of bimetallic electrocatalyst. It should be noted, that there are rarely commercially available Pt-based bimetallic electrocatalysts for oxygen reduction reaction. On the other side, the laboratory synthesized majority of the bimetallic electrocatalysts used for ORR. Yet need to be improved to achieve the performance similar to the commercial single metal Pt electrocatalyst with high Pt metal content. In view of this Pt-based bimetallic cathode electrocatalyst for ORR is very much efficient. The present thesis focuses on the synthesis of the Pt-based electrocatalyst for subsequent use in the H 2 based proton exchange membrane fuel cell. It should be noted that the synthesis method and solvent used is the process both play an important role. Till date, no detailed research on the synthesis of cathode electrocatalysts utilizing various types of solvents, as well as thorough characterization of the synthesized electrocatalyst had not been reported. In this regard, bimetallic Pt-Co and Pt-Ni electrocatalysts for effective ORR in hydrogen-based PEMFCs were synthesized in the laboratory utilizing various solvents. The composition of the metal were varied to manufacture four different types of bimetallic cathode electrocatalyst. Four different types of solvents were used namely, dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), and ethylene glycol (EG) and Water Indian institute of Technology IIT (BHU), Varanasi Page | 22 Chapter 2
