Polymer electrolyte membranes for direct methanol fuel cells

POLYMER ELECTROLYTE MEMBRANES FOR DIRECT METHANOL FUEL CELLS PEI HAIQIN NATIONAL UNIVERSITY OF SINGAPORE 2007 POLYMER ELECTROLYTE MEMBRANES FOR DIRECT METHANOL FUEL CELLS PEI HAIQIN (M.SCI., Tianjin University) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMICAL & BIOMOLECULAR ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2007 ACKNOWLEDGEMENTS First of all, I genuinely wish to express my deepest appreciation and thanks to my supervisors, Professor Lee Jim Yang and Associate Professor Hong Liang, for their intellectually-stimulating guidance and invaluable encouragement throughout my candidature as a Ph.D student at the National University of Singapore. Professor Lee’s comprehensive knowledge and incisive insight on fuel cell materials as well as his uncompromising and prudent attitude toward research and insistence on quality works have deeply influenced me and will definitely benefit my future study. His invaluable advice, patience, constant encouragement and painstaking revisions of my manuscripts and this thesis are indispensable to the timely completion of this project. I am also grateful to Professor Hong Liang. His immense background and experience in polymer materials enabled me to work through many technical problems smoothly. His selfless help was indispensable to the completion of my thesis work. I am grateful for the Research Scholarship from the National University of Singapore (NUS) that enables me to pursue my Ph.D degree. I am also indebted to the Department of Chemical & Biomolecular Engineering of NUS for the research infrastructure support. Thanks are also due to my fellow students and researchers in our group, Dr. Yang Jun, Mr. Zeng Jianhuang, Miss Liu Fang, Dr. Zhou Weijiang, Mr. Zhang Shuo, Mr. Zhang Qingbo, Mr. Yang Jinhua, Mr. Dengda and the laboratory technicians, for all the handy helps, technical supports, invaluable discussion and suggestions. Last but not least, I am most grateful to my family, especially my parents and my husband, for their absolute love, encouragement and support during my struggle for my Ph.D’s degree in Singapore. i TABLE OF CONTENTS ACKNOWLEDGEMENT i TABLE OF CONTENTS ii SUMMARY viii LIST OF FIGURES xi LIST OF TABLES xv LIST OF SCHEMES CHAPTER INTRODUCTION xvi 1.1 Background 1.2 Objective and Scope of Thesis 1.3 Organization of This Thesis CHAPTER LETERATURE REVIEW 2.1 Fuel Cell 2.2 The Development of Polymer Electrolyte Membranes 15 2.3 Performance Indicators for Polymer Electrolyte Membranes 18 2.3.1 Proton Conductivity 18 2.3.2 Methanol Crossover 20 2.3.3 Water Uptake and Degree of Swelling 23 2.3.4 Mechanical Properties 24 2.3.5 Other Requirements for PEMs 24 2.4 Modifications of Nafion® Membrane 25 ii 2.4.1 Bulk Modifications of Nafion® Membrane 25 2.4.2 Surface Modifications of Nafion® Membranes 28 2.5 Alternative PEMs Materials and Their Composites 30 2.5.1 Acid-base Polymer Membranes 30 2.5.2 Non-Nafion® based Inorganic-Organic Composite Membrane 34 2.5.3 New Polymer Electrolyte Membranes 37 CHAPTER EMBEDDED POLYMERIZATION DRIVERN 46 ASYMMETRIC PEM FOR DIRECT METHAOL FUEL CELLS 3.1 Introduction 46 3.2 Experimental 50 3.2.1 Materials 50 3.2.2 Preparation of Solution-Cast Membranes 51 3.2.3 Materials Characterizations 52 3.2.4 Water Uptake 54 3.2.5 Solvent Etching Test 54 3.2.6 Proton Conductivity 54 3.2.7 Swelling Tests in Methanol Solution 55 3.2.8 Dimensional Changes in Water and Methanol Solution 55 3.3 Results and Discussions 56 3.3.1 Structural and Swelling Characteristics of the TCPB Membrane 56 3.3.2 Embedded Polymerization-Induced Structural Changes 59 3.3.3 Thermal and Mechanical Properties 65 3.3.4 Proton Conductivity and Swelling Tests in Methanol 68 iii 3.3.5 Dimensional Stability in Water and Methanol Solutions 3.4 Conclusion CHAPTER POLYMER ELECTROLYTE MEMBRANE BASED ON 71 73 74 2-ACRYLAMIDO-2-METHYL PROPANESULFONIC ACID FABRICATED BY EMBEDDED POLYMERIZATION 4.1 Introduction 74 4.2 Experimental 74 4.2.1 Materials 75 4.2.2 Membrane Preparations 75 4.2.3 Membrane Characterizations 76 4.3 Results and Discussions 81 4.3.1 Embedded Polymerization-Induced Membrane Structure 81 4.3.2 Water Uptake and Ion-Exchange Capacity (IEC) 82 4.3.3 Proton Conductivity 85 4.3.4 Methanol Permeability 87 4.3.5 Mechanical Properties 89 4.4 Conclusion CHAPTER EMBEDDED HYDROPHILIC NANO-GRANULES WITH 91 92 RADIATING PROTON-CONDUCTING CHANNELS IN A HYDROPHOBIC MATRIX 5.1 Introduction 92 5.2 Experimental 94 5.2.1 Materials 94 iv 5.2.2 Membrane Preparation 94 5.2.3 Materials Characterizations 96 5.2.4 Water Sorption and State of Water 97 5.2.5 Ion Exchange Capacity (IEC) 97 5.2.6 Proton Conductivity 98 5.2.7 Methanol Permeability 99 5.2.8 Viscosity 99 5.3 Results and Discussions 100 5.3.1 Structure of the AMPS Copolymer-TCPB Blend 100 5.3.2 Structure-Dependent Water Uptake and Ion Exchange Capacity 108 5.3.3 Proton Conductivity 110 5.3.4 Methanol Permeability 114 5.4 Conclusion CHAPTER EFFECTS OF POLYANILINE CHAIN STRUCTURES ON 116 118 PROTON CONDUCTION IN A PEM HOST MATRIX 6.1 Introduction 118 6.2 Experimental Section 119 6.2.1 Materials 119 6.2.2 Preparation of Polyaniline 120 6.2.3 Preparation of PAn-AMPS-PEM 121 6.2.4 Characterizations 123 6.3 Results and Discussions 6.3.1 The Chain Configurations of Polyanilines 124 124 v 6.3.2 Oxidation State of Polyanilines 128 6.3.3 Interaction of PAn Colloidal Particles with P(AMPS-HEMA) 131 6.3.4 Promotional Effect of PAn on Proton Transport in the PEM Matrix 6.4 Conclusion CHAPTER POLYMER ELECTROLYTE MEMBRANES BASED ON 135 139 140 CROSSLINKED AMPHIPHILIC COPOLYMERS OF 3-SULFOPROPYL METHACRYLATE 7.1 Introduction 140 7.2 Experimental 142 7.2.1 Materials 142 7.2.2 Membrane Preparation 143 7.2.3 Characterizations of SPM Membranes 146 7.2.4 Ion Exchange Capacity (IEC) 146 7.2.5 Water Uptake 147 7.2.6 Proton Conductivity 147 7.2.7 Methanol Permeability 148 7.3 Results and Discussions 148 7.3.1 Structural Characteristic of the SPM Membranes 148 7.3.2 Structure-Dependent Water Uptake and Ion Exchange Capacity 153 7.3.3 Thermal Stability 156 7.3.4 Proton Conductivity 157 7.3.5 Methanol Permeability 160 7.4 Conclusion 162 vi CHAPTER CONCLUSIONS & RECOMMENDATIONS 164 REFERENCE 168 vii Summary This thesis study is aimed at producing proton-conducting polymer electrolyte membranes (PEMs) for direct methanol fuel cells (DMFCs), using relatively inexpensive monomers or polymers. A number of preparation methods and their variations have been explored, with fairly extensive characterizations of the resulting PEMs (Fourier transform infrared spectroscopy, thermal gravimetric analysis, scanning electron microscopy, differential scanning calorimetry and X-ray photoelectron spectroscopy). The properties of most relevance to DMFC applications, especially proton conductivity and methanol permeability, were measured and compared with those of Nafion®. The first method made use of a three-component acrylic polymer blend (TCPB) consisting of poly(4-vinylphenol-methyl methacrylate) P(4-VP-MMA), poly(butyl methacrylate) (PBMA) barrier. and Paraloid® B-82 acrylic copolymer resins as the methanol 2-acrylamido-2-methyl propanesulfonic acid (AMPS), 2-hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol)dimethylacrylate (PEGDMA) were introduced to the TCPB matrix and polymerized there using embedded polymerization. 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Optimisation of Polypyrrole/Nafion Composite Membranes for Direct Methanol Fuel Cells, Electrochimica Acta, 51, pp.4052-4060. 2006. 185 [...]... 2003; Sopian and Daud, 2006) 11 The general design of most fuel cells is similar except for the electrolyte The five major types of fuel cells as defined by their electrolyte are: alkaline fuel cells (AFCs), phosphoric acid fuel cells (PAFCs), molten carbonate fuel cells (MCFCs), solid oxide fuel cells (SOFCs) and polymer electrolyte membrane fuel cells (PEMFCs) Their main features and intended applications... on fuel cells have been ongoing ever since the first fuel cell was demonstrated in the mid 19th century 1 Among various types of fuel cells, the direct methanol fuel cells (DMFCs) are an attractive option for portable and electric vehicle applications because they offer advantages such easy refueling and a simplified system design (Gogel, et al., 2004; Yang and Manthiram, 2004) The DMFCs work on methanol. .. by a succinct but fairly updated account of recent development in the direct methanol fuel cells (DMFCs), focusing on topics which are most relevant to this thesis study: polymer electrolyte membranes (PEMs), methanol crossover and the prevailing methods of preparation of PEMs for DMFC applications 2.1 Fuel Cell The principles of fuel cell were discovered in 1839 by Sir William R Grove, using the reaction... methanol directly without the need for onboard fuel reforming into hydrogen Their quick start-up characteristics and the ability to operate at relatively low temperatures compare favorably with hydrogen polymer electrolyte membrane fuel cells (PEMFC) At present, one of the major impediments to the commercialization of DMFCs is methanol crossover from the anode to the cathode through the polymer electrolyte. .. general introduction to the polymer electrolyte membranes 2.2 The Development of Polymer Electrolyte Membranes The success of PEMFCs is owed to a large part to the availability of good polymer electrolyte membranes The first generation membranes used in the sixties were based on polystyrene sulfonic acids and were infamous for their degradation problem They were replaced by membranes based on perfluorosulfonic... TCPB, M-0 and M-1 membranes (b) M-3 and M-4 membranes 68 xi Fig.3.10 Effect of sulfonic group content on membrane proton conductivity 70 Fig.3.11 Extent of water and methanol uptakes for various tested membranes 70 Fig.3.12 Volume expansions of AMPS membranes in water after 24h 72 Fig.3.13 Volume expansions of AMPS membranes in 90% methanol solutions after 24h 72 Fig 4.1 The diagram of methanol diffusion... melting curve of hydrated B3 and B4 membranes 109 Fig 5.7 Proton conductivities of AMPS copolymer –TCPB blend membranes 111 Fig 5.8 Temperature dependence of proton conductivity of AMPS copolymer-TCPB blend membranes and Nafion®117 113 Fig 5.9 Methanol permeabilities of Nafion®117 and AMPS copolymer-TCPB blend membranes 115 Fig 5.10 Viscosity of TCPB at MEK and methanol- containing MEK 116 Fig.6.1 FESEM... 2 → 2 H + + 2e − Electrolyte Air + Water Cathode O2 + 4 H + + 4 e − → 2 H 2 O Figure 2.1 Principles of PEMFCs 12 However, the acceptance of hydrogen fuel cells has been hampered by nontrivial issues such as hydrogen storage and refueling The wide availability and portability of methanol as a liquid fuel has made DMFC a very attractive alternative to hydrogen fuel cells Compared to fuel cell systems... the anode leaving little un-reacted methanol to diffuse through the electrolyte and onto the cathode (2) The fuel to the anode is controlled Clearly, the lower the methanol concentration at the anode, the lower it will be in the electrolyte, and hence at the cathode 14 (3) Thicker electrolyte membranes than what is normal for PEMFCs are used This will clearly reduce fuel crossover but at the expense... electrolyte membrane Methanol crossover not only wastes fuel but also causes performance losses at the cathode due to the creation of a mixed potential and catalyst deactivation (Tricoli, et al., 2000; Choi, et al., 2001; Shao and Hsing, 2002) While poly(perfluorosulfonic acid) (Nafion®) membranes are the most commonly used solid polymer electrolyte in fuel cells, they are not suitable for DMFC applications . POLYMER ELECTROLYTE MEMBRANES FOR DIRECT METHANOL FUEL CELLS PEI HAIQIN NATIONAL UNIVERSITY OF SINGAPORE 2007 POLYMER ELECTROLYTE MEMBRANES FOR DIRECT. 9 2.1 Fuel Cell 9 2.2 The Development of Polymer Electrolyte Membranes 15 2.3 Performance Indicators for Polymer Electrolyte Membranes 18 2.3.1 Proton Conductivity 18 2.3.2 Methanol. aimed at producing proton-conducting polymer electrolyte membranes (PEMs) for direct methanol fuel cells (DMFCs), using relatively inexpensive monomers or polymers. A number of preparation methods