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An Electrochemical and Spectroscopic ... i An Electrochemical and Spectroscopic Investigation of Nickel Electrodes in Alkaline Media for Applications in Electro-Catalysis David S

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  • i

    An Electrochemical and Spectroscopic Investigation of Nickel

    Electrodes in Alkaline Media for Applications in Electro-Catalysis

    David S. Hall

    Thesis submitted to the

    Faculty of Graduate and Postdoctoral Studies

    In partial fulfillment of the requirements

    For the PhD degree in Chemistry

    Department of Chemistry

    Faculty of Science

    University of Ottawa

    © David Hall, Ottawa, Canada, 2014

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    Abstract

    Nickel-based catalysts in aqueous alkaline media are low-cost electrode materials for

    electrolytic hydrogen generation, a renewable method of producing fuel and industrial feedstock.

    However, further work is necessary to develop inexpensive electro-catalyst materials with high

    activity and long-term stability. This thesis employs spectroscopic and electrochemical methods

    to directly address specific research problems for the development of improved materials and

    devices with commercial or industrial value. The first chapter reviews the applications of nickel

    electrodes; the structures of nickel, nickel hydroxides, and nickel hydrides; and techniques for

    measuring the electrochemically active surface area (AECSA) of nickel. In the second chapter,

    electrochemically precipitated nickel hydroxide materials are fully characterized by Raman

    spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, X-ray photoelectron

    spectroscopy (XPS), and X-ray diffraction (XRD). This work unifies and simplifies the large

    body of literature on the topic by considering two fundamental phases, α- and β-Ni(OH)2, and

    various types and extents of structural disorder. The third chapter examines and demonstrates the

    potential applications of in situ Raman spectroscopy by monitoring the spontaneous ageing of α-

    Ni(OH)2 to β-Ni(OH)2 in pure water at room temperature. The fourth chapter considers the

    longstanding problem of electrode deactivation, the gradual decrease in nickel electro-catalyst

    activity during prolonged hydrogen production. Voltammetric and XRD evidence demonstrates

    that hydrogen atoms can incorporate into the electrode material and cause structural disorder or

    the formation of α-NiHx and β-NiHx at the surface. The voltammetric formation of NiOx, α-

    Ni(OH)2, β-Ni(OH)2, and β-NiOOH surface species are examined by electrochemical and XPS

    measurements. The fifth chapter of this thesis presents a new method to measure the AECSA of

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    nickel, in situ, by the addition of an oxalate salt to the alkaline electrolyte. Oxalate adsorbs onto

    the (001) surface of the surface Ni(OH)2, as evidenced by voltammetric and attenuated total

    reflectance (ATR) FT-IR spectroscopy measurements. The adsorbed oxalate limits the surface

    hydroxide to a single layer. The surface NiOOH/Ni(OH)2 reduction peak during the reverse scan

    may be used to accurately and precisely measure the AECSA. The error of this method is estimated

    at < 10 %.

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    Table of Contents

    Abstract ........................................................................................................................................... ii

    Acknowledgements ....................................................................................................................... vii

    Table of Tables .............................................................................................................................. ix

    Table of Figures ............................................................................................................................. xi

    List of Abbreviations .................................................................................................................... xv

    1. General Introduction .............................................................................................................. 1

    1.1. Nickel Electrodes and Applications in Electro-catalysis ........................................ 2

    1.2. Electrode Materials ................................................................................................. 3

    1.2.1. Nickel ............................................................................................................. 3

    1.2.2. Nickel Hydroxides.......................................................................................... 5

    1.2.1. Nickel Hydrides............................................................................................ 21

    1.3. Electrochemically Active Surface Area (AECSA) Measurements .......................... 24

    1.4. Thesis Objectives .................................................................................................. 27

    2. Raman and Infrared Spectroscopy of α and β Phases of Nickel Hydroxide ....................... 29

    2.1. Introduction ........................................................................................................... 30

    2.2. Experimental Methods .......................................................................................... 31

    2.2.1. Material Preparation ..................................................................................... 31

    2.2.2. X-Ray Diffraction (XRD) ............................................................................ 33

    2.2.3. X-Ray Photoelectron Spectroscopy (XPS) .................................................. 33

    2.2.4. Raman Spectroscopy .................................................................................... 34

    2.2.5. Fourier Transform Infrared (FT-IR) Spectroscopy ...................................... 36

    2.3. Results and Discussion .......................................................................................... 36

    2.3.1. X-Ray Diffraction Patterns........................................................................... 36

    2.3.2. X-Ray Photoelectron Spectra ....................................................................... 39

    2.3.3. Raman Spectra.............................................................................................. 41

    2.3.4. Infrared Spectra ............................................................................................ 43

    2.3.5. Vibrational Modes of β-Ni(OH)2 ................................................................. 45

    2.3.6. Vibrational Modes of α-Ni(OH)2 ................................................................. 61

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    2.3.7. Nitrate Bands ................................................................................................ 70

    2.3.8. Sulfate Bands................................................................................................ 71

    2.3.9. Fluorescence ................................................................................................. 72

    2.3.10. Disorder ........................................................................................................ 73

    2.4. Conclusions ........................................................................................................... 74

    3. Applications of In Situ Raman Spectroscopy for Identifying Nickel Hydroxide Materials

    and Surface Layers During Chemical Aging ....................................................................... 76

    3.1. Introduction ........................................................................................................... 77

    3.2. Methods ................................................................................................................. 77

    3.2.1. Material Preparation ..................................................................................... 77

    3.2.2. Raman Spectroscopy .................................................................................... 78

    3.2.3. α-Ni(OH)2 Film Aging ................................................................................. 79

    3.3. Results and Discussion .......................................................................................... 79

    3.3.1. Raman Spectroscopy of Ni(OH)2 Films Immersed in Water ....................... 79

    3.3.2. In Situ Raman Spectroscopy of Film Aging in Room Temperature Water . 89

    3.4. Conclusions ......................................................................................................... 101

    4. Electrochemistry of Metallic Nickel in Alkaline Media ................................................... 103

    4.1. Introduction ......................................................................................................... 104

    4.2. Experimental Methods ........................................................................................ 105

    4.2.1. Electrode Preparation ................................................................................. 105

    4.2.2. Electrochemical Experiments ..................................................................... 106

    4.2.3. X-ray Diffraction (XRD) ............................................................................ 107

    4.2.4. X-ray Photoelectron Spectroscopy (XPS) .................................................. 107

    4.3. Results and Discussion ........................................................................................ 107

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