THE FEASIBILITY OF A UNITISED REGENERATIVE FUEL CELL WITH A REVERSIBLE CARBON-BASED HYDROGEN STORAGE ELECTRODE A thesis submitted in fulfillment of the requirements for the degree of Master of Engineering by Research Mohammad Javad Jazaeri B.Sc. School of Aerospace, Mechanical and Manufacturing Engineering College of Science, Engineering and Health RMIT University August 2013 Master of Engineering by Research ACKNOWLEDGMENT ACKNOWLEDGMENTS I would like to thank my supervisor, Associate Professor John Andrews, for sharing his ideas, knowledge, and insights. I am very grateful for his tireless efforts in providing guidance, feedback and constant motivation during this program. I would like to express my gratitude to Dr Fugen Daver (RMIT University) for suggesting saturated salt solutions in obtaining constant relative humidities and also for granting me access to the chemistry lab, the BET measurement analyser, and the hot-press machine. I would also like to thank Dr Anthony O'Mullane (RMIT University) for sharing his knowledge in electrochemical impedance spectroscopy (EIS) and for spending his valuable time to help me with the EIS measurements. I would like to thank Professor Aliakbar Akbarzadeh (RMIT University) for his encouragement and financial support in the duration of this program. I truly appreciate the opportunities that Dr Abhijit Date and Dr Asintha Nanayakkara from RMIT University have given me to experience teaching and tutoring. Many thanks go to Mr Saeed Seif Mohammadi (MEng graduate, RMIT University) who selflessly shared his experience on the URFC set-ups. I would like to thank Mr Amandeep Oberoi (PhD candidate, RMIT University) for being my lab-mate. I also would like to thank many good friends in the Energy CARE group who shared good times and bad times with me. If I wanted to name everybody who has inspired, taught and encouraged me along the way, this section would have been several pages long. I would like to thank Ms Zahra Homan from School of Applied Sciences (RMIT University) for her technical assistance in the chemistry lab. I also would like to acknowledge Professor Alan Chaffee (Monash University) and Mr Lachlan Ciddor (PhD candidate, Monash University) for providing a number of activated carbons. I would like to acknowledge the facilities, and the scientific and technical assistance, of the Australian Microscopy & Microanalysis Research Facility at the RMIT Microscopy & I Master of Engineering by Research ACKNOWLEDGMENT Microanalysis Facility. In particular, I would like to thank Mr Phil Francis and Mr Peter Rummel. I would like to thank Mr Patrick Wilkins and Mr David Goodie from the School of Aerospace, Mechanical, and Manufacturing Engineering workshop at RMIT University for manufacturing the experimental cell and guiding me in modifying the designs. I would like to express my gratitude to Ms Lina Bubic and Ms Emilija Simic from RMIT University for their administrative assistance throughout this program. I would like to thank Ms Wendy Haszler from RMIT University library for her assistance in finding some of the references. I also would like to acknowledge the generous International Conference Grant from the School of Graduate Research, RMIT University. I heartily thank my family for their never-ending love, encouragement, and for always being there for me. I would like to dedicate whatever I have achieved in the past two years to them. II Master of Engineering by Research DECLARATION DECLARATION I, Mohammad Javad Jazaeri, hereby submit the thesis entitled “The Feasibility of a Unitised Regenerative Fuel Cell with a Reversible Carbon-Based Hydrogen Storage Electrode” for the degree of Master of Engineering by Research and certify that except where due acknowledgement has been made, the work is that of the author alone; the work has not been submitted previously, in whole or in part, for any other academic award and that the content of the thesis is the result of work that has been carried out since the official commencement of the program. Mohammad Javad Jazaeri 30 August 2013 III Master of Engineering by Research TABLE OF CONTENTS TABLE OF CONTENTS 1 INTRODUCTION 1 1.1 ROLE OF HYDROGEN IN A SUSTAINABLE ENERGY STRATEGY 1 1.2 HYDROGEN STORAGE TECHNOLOGIES 3 1.3 ELECTROCHEMICAL STORAGE OF HYDROGEN 6 1.4 THE PROTON FLOW BATTERY CONCEPT 7 1.5 SIGNIFICANCE OF THE RESEARCH 8 1.6 OBJECTIVES OF THE PROJECT 9 1.7 RESEARCH QUESTIONS 10 1.8 SCOPE 10 1.9 EXPECTED OUTCOMES 11 1.10 NOVELTY OF THE PROJECT 11 1.11 STRUCTURE OF THE THESIS 12 2. RESEARCH DESIGN AND METHOD 14 2.1 OVERVIEW 14 2.2 GENERAL METHODOLOGICAL APPROACH 14 2.3 EXPERIMENTAL PROCEDURES 14 2.4 INSTRUMENTATION AND COLLECTING DATA 16 2.5 ACTIVITIES 17 3. THE CONCEPT OF A REVERSIBLE URFC WITH AN 20 INTEGRATED CARBON HYDROGEN STORAGE ELECTRODE 3.1 COMPONENTS OF A HYDROGEN SYSTEM 20 3.1.1 PEM electrolysers 20 3.1.2 Methods of hydrogen storage 22 3.1.2.1 High-pressure hydrogen storage 22 3.1.2.2 Liquid hydrogen 24 3.1.2.3 Hydrogen sorption in solid state 25 3.1.2.4 Chemically bonded hydrogen storage liquids 26 3.1.3 PEM fuel cell 26 3.1.4 Structure and principles of a PEM URFC 27 3.2 CONVENTIONAL HYDROGEN SYSTEMS 30 3.2.1 A hydrogen system employing an electrolyser, storage unit, and fuel cell 30 3.2.2 A hydrogen system employing a URFC and storage unit 32 3.3 INTEGRATED HYDROGEN STORAGE IN A PEM URFC 34 3.3.1 The concept of the proton flow battery 34 3.3.2 Benefits and potential applications of a proton flow battery 35 3.4 PREVIOUS WORK ON THE CONCEPT OF INTEGRATING 36 HYDROGEN STORAGE ELECTRODE IN URFC 3.4.1 History of the concept 36 3.4.2 General Electric Company and a rechargeable fuel cell 45 3.4.3 Electrochemical storage of hydrogen in activated carbon 51 3.4.4 Recent work on the concept of proton flow battery at RMIT University 57 IV Master of Engineering by Research TABLE OF CONTENTS 3.5 SOLID STATE HYDROGEN STORAGE IN ACTIVATED CARBON 58 3.5.1 Activated carbon as the medium for hydrogen storage 58 3.5.2 Mechanism of electrochemical storage of hydrogen in activated carbon 59 3.6 Conclusions 60 3.6.1 Limitations of previous studies and areas requiring R&D 60 3.6.2 Towards realisation of the concept of a proton flow battery with activated 61 carbon electrode 4. FABRICATION AND CHARACTERISATION OF 62 ACTIVATED CARBON-NAFION COMPOSITE MATERIALS 4.1 FABRICATING ACTIVATED CARBON 62 4.1.1 Preparation and characterisation of precursors 62 4.1.1.1 Precursors 62 4.1.1.2 Morphology of precursors 64 4.1.1.3 Elemental analysis of precursors 68 4.1.2 Activation techniques 72 4.1.2.1 Physical activation 72 4.1.2.2 Chemical activation 73 4.1.2.3 Replica technique 75 4.1.2.4 Selecting the activation technique 75 4.1.3 Activating precursors with chemical activation technique 76 4.1.3.1 Carbonisation 76 4.1.3.2 Impregnation 77 4.1.3.3 Activation 78 4.1.3.4 Washing 79 4.1.3.5 Drying 80 4.1.3.6 Summary of the KOH activation procedures 81 4.1.4 Activated carbons from Monash University 83 4.2 CHARACTERISTICS OF ACTIVATED CARBONS AND SELECTING 83 SAMPLES FOR COMPOSITE MATERIALS 4.2.1 Porosity measurement 83 4.2.1.1 Models of activated carbon and the concept of porosity 83 4.2.1.2 Adsorption isotherm analysis method 85 4.2.1.3 CO2 and N2 adsorption isotherms 90 4.2.1.4 Summary of porosity tests on the activated carbons 92 4.2.2 Selecting samples for fabricating composite material 94 4.2.2.1 Influential factors in selecting samples 94 4.2.2.2 Selecting samples for fabrication of composite electrodes 94 4.3 FABRICATION OF COMPOSITE MATERIALS 95 4.3.1 Ingredients for composite materials 95 4.3.1.1 Nafion solution 95 4.3.1.2 Activated carbons 97 4.3.2 Mixing nafion and selected activated carbon samples 97 4.3.3 Fabricating of the composite materials 99 4.3.3.1 Solution casting of the composite materials 99 4.3.3.2 Size and number of the composite samples 100 4.3.4 Protonation of composite materials 101 4.3.5 Investigation of proper dispersion of activated carbon in nafion 101 V Master of Engineering by Research TABLE OF CONTENTS 4.4 SETTING UP DIFFERENT RELATIVE HUMIDITY ENVIRONMENTS 107 4.4.1 Design and manufacturing of a relative humidity chamber 107 4.4.2 Test points in environments at various relative humidities 109 4.5 PHYSICAL BEHAVIOUR OF THE COMPOSITE MATERIALS IN 109 DIFFERENT RELATIVE HUMIDITY ENVIRONMENTS 4.5.1 Measurements of the composites in different relative humidity 109 environments 4.5.2 Water uptake of the composite materials 111 4.5.3 Swelling of the composite materials 115 4.6 MEASUREMENT OF ELECTRON AND PROTON CONDUCTIVITY 117 OF THE COMPOSITE MATERIALS 4.6.1 Electrochemical impedance spectroscopy 117 4.6.2 Design and manufacturing the test cell for EIS method 119 4.6.3 Equivalent circuit 120 4.6.3.1 Equivalent circuit of nafion membrane 120 4.6.3.2 Equivalent circuit of composite material 122 4.6.4 Electrochemical characterisation of the test set-up 125 4.6.4.1 Identifying values of EIS test rig 125 4.6.4.2 Proton conductivity of Nafion 115 membrane 126 4.6.5 Proton conductivity of the composite materials 127 4.6.6 Electron conductivity of the composite materials 129 4.7 SELECTING THE COMPOSITE MATERIALS FOR FABRICATING 132 FULL-SIZE COMPOSITE ELECTRODES 4.7.1 Overview of electron and proton conductivity of the composite materials 132 4.7.2 Selection of materials for test electrodes 133 4.8 ANALYSIS OF THE PHYSICAL AND ELECTROCHEMICAL 135 CHARACTERISTICS OF THE COMPOSITE MATERIALS 4.8.1 Water uptake of the composite materials in different relative humidity 135 environments 4.8.2 Volumetric swelling of the composite materials in different relative 136 humidity environments 4.8.3 Proton conductivity of the composite materials in different relative 137 humidity environments 4.8.4 Electron conductivity of the composite materials in different relative 138 humidity environments 4.9 OTHER APPLICATIONS FOR THE FABRICATED COMPOSITE 139 MATERIALS 5.