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(20Khz) Production of Hydrogen from Aqueous Solutions

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(20Khz) Production of Hydrogen from Aqueous Solutions SONOELECTROCHEMICAL (20 kHz) PRODUCTION OF HYDROGEN FROM AQUEOUS SOLUTIONS BY DANIEL SYMES Thesis submitted in accordance with the requirements of The University of Birmingham for the degree of MASTER OF RESEARCH School of Chemical Engineering College of Engineering and Physical Sciences The University of Birmingham February 2011 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder. ACKNOWLEDGEMENTS I am whole heartily thankful to my supervisor Dr Bruno G. Pollet, whose encouragement, supervision, and support from the preliminary to concluding level enabled me to develop and understanding of the subject. I would also like to express my gratitude to the EPSRC for providing the funding for this research, and thank my family and girlfriend for their love and support throughout. Finally I offer my regards to Matthew Lepesant whose assistance in the laboratory was of great aid to me, blessings to Professor Kevin Kendall, Dr Waldemar Bujalski, Dr Aman Dhir, Oliver Curnick, James Courtney, Tony Meadowcroft and fellow researchers at the PEM Fuel Cell Research Group and the Centre for Hydrogen and Fuel Cell Research at the University of Birmingham, who supported me in any respect during the completion of the project. ABSTRACT There are various methods of producing Hydrogen. These include electrolysis, which this work is based upon, and steam reforming; currently the most commercially viable method. The research herein investigates methods of producing ‘green’ Hydrogen more efficiently by using ultrasound (20 kHz) combined to electrolysis. Previous studies have shown that ultrasound enhances mass-transfer of electro-active species from the bulk solution to the electrode surface in any electrolytic system and mechanically removes gas bubbles on the electrode surface. This work takes this previous research further by quantifying actual hydrogen gas output. The hydrogen evolution reaction was then directly compared with that calculated using the Ideal Gas Equation to quantify the efficiency of the electrolysis system. It was observed that ultrasound lowers the anodic and cathodic overpotentials due to gas removal at the electrode surface induced by cavitation and increased mass-transfer. However, it was found that ultrasound did not increase the rate of Hydrogen production. During experimentation it was seen that the force exhibited on the electrodes by ultrasonic waves limited bubble evolution on the electrode surface. Issues associated with the ultrasonic reactor geometry and the ultrasonic transducer size are also discussed as potential reasons for this result. CONTENTS 1. INTRODUCTION & LITERATURE SURVEY ............................................................................................. 1 1.1 Global Warming and Carbon Dioxide ............................................................................................ 1 1.2 Hydrogen as an Energy Carrier ...................................................................................................... 4 1.2.1 What is Hydrogen? ................................................................................................................. 4 1.2.2 Methods of Hydrogen Production ......................................................................................... 6 1.2.3 Fuel Cell Technology ............................................................................................................. 13 1.3 Principles of Electrochemistry ..................................................................................................... 17 Method 1: Decomposition Voltage ............................................................................................... 19 Method 2: Discharge Potential ..................................................................................................... 20 1.4 Electrolysis ................................................................................................................................... 22 1.5 Sonoelectrochemistry ................................................................................................................. 25 1.6 Sonoelectrochemical Production of Hydrogen ........................................................................... 30 2. EXPERIMENTAL METHOD .................................................................................................................. 33 2.1 Equipment & Parameters ............................................................................................................ 37 3. RESULTS AND DISCUSSION ................................................................................................................ 38 3.1 Preliminary Experiments ............................................................................................................. 38 3.1.1 Current Voltage Curves ........................................................................................................ 38 3.1.2 Overpotential Determination ............................................................................................... 43 3.2 Custom Glassware Experiments .................................................................................................. 46 3.2.1 Current-Voltage Curves ........................................................................................................ 46 3.2.2 Hydrogen Evolution Rate ..................................................................................................... 49 3.2.3 Hydrogen Efficiency Data ..................................................................................................... 53 3.2.4 Energy Efficiency Data .......................................................................................................... 56 3.2.5 Ultrasonic Power Determination ......................................................................................... 56 3.3 Erosion of the Electrodes ............................................................................................................ 57 3.4 Experiments with Industrial Electrolysers ................................................................................... 58 3.4.1 Introduction.......................................................................................................................... 58 3.4.2 Data Analysis ........................................................................................................................ 60 4. CONCLUSIONS ................................................................................................................................... 63 4.1 Comparison for Industrial Electrolyser and Sonoelectrochemical Cell ....................................... 66 5. FUTURE WORK .................................................................................................................................. 69 5.1 Electrolytes .................................................................................................................................. 69 5.2 Electrode Parameters .................................................................................................................. 70 5.3 Electrolyte Temperature ............................................................................................................. 70 5.4 Ultrasonic Parameters ................................................................................................................. 71 6. REFERENCES ...................................................................................................................................... 72 7. APPENDICES ...................................................................................................................................... 77 7.1 Appendix I - Data Tables .............................................................................................................. 77 7.1.1 Preliminary Experiments ...................................................................................................... 77 7.1.2 Custom Glassware Experiments ........................................................................................... 83 7.2 Appendix II - Graphs .................................................................................................................. 143 7.2.1 Preliminary Experiments .................................................................................................... 143 7.2.2 Custom Glassware Experiments ......................................................................................... 146 7.3 Appendix III – Decomposition Potential Calculations ............................................................... 155 7.4 Appendix IV - Ultrasound Power Data Tables ........................................................................... 158 7.5 Appendix V - Health & Safety .................................................................................................... 159 7.6 Appendix VI – Conferences Attended & Posters Presented ....................................................
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