Electrochemical Deposition and Electrocatalytic Properties of Multilayered Nanoclusters of Platinum and Gold

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Nanoscale materials

The physical and chemical properties of nanoscale materials (usually defined in the 1 – 100 nanometre range) are of enormous interest and ever-increasing significance for current and future scientific and technological applications. Materials reduced to the nanoscale can remarkably show very different properties compared to what they exhibit on a macroscale or bulk matter, enabling unique applications. Properties such as magnetism, optics, melting point temperature, latentn heat of fusion, and surface reactivity can be remarkably affected by the nature of the nanoscale substances [1-4].
Research efforts continue to find applications of nanoscale materials (nanomaterials), with potential impact to shape the modern society, in areas such as energy production and storage [5], healthcare [6], water purification and pollution control [7]. Indeed, versatile chemical and electrical energy conversion, facilitated at atomic and molecular levels with cost-effective materials, is of fundamental and technological importance in our modern world constrained by requirements for adjustment in sustainable utilisation of fossil minerals and fuels. Nanoscale objects have always existed in nature, both in the living and non-living systems (Most biological processes occur at these minute scales). Most sophisticated biological processes, such as protein assembly and photosynthesis, involve nanostructured units. Solids such as clays and minerals formed geologically in the natural world also occur as nanoscale entities [8].
The correlation between properties and particle size has been known since the nineteenth century, when Michael Faraday demonstrated that the colour of colloidal gold particles can be modified via changes in the size of the constituent particles, albeit, with no in-depth knowledge of the actual dimensions of the particles he synthesized, which are now known to have been in the range of 12 – 60 nm as a result of advances in microscopic techniques in the twentieth century [9]. Despite the occurrence in nature and a few historical products, the size-related aspects of nanoscale materials had not been focused on explicitly by the scientific community until evolution of new tools capable of monitoring and manipulating materials at the nanoscale became available in recent times [8]. The quest to construct tiny objects, atom-by-atom or molecule-by-molecule, is in the realm of the exciting prospects of the emerging fields of ‘Nanoscience’ and ‘Nanotechnology’. Nanoscience involves the study of materials on the nanoscale level between approximately 1 and 100 nm [10] as well as the study of how to control the formation of two- and three-dimensional assemblies of molecular scale building blocks into well-defined nanostructures or nanomaterials [11].
Nanotechnology relates to such activities undertaken to build functional devices based on the controlled assembly of nanoscale objects, for specific technological applications [8]. and metal oxides. In solid-state, these materials can further be classified as (i) nanomaterials with property changes related directly to size (that is, changes occur as the size of a solid material is reduced to nanoscale); and (ii) nanostructured solids that can be uniquely assembled atom-by-atom to create a completely different materials, not just a smaller fragment of a larger solid [8]. Nanoscience is highly cross-disciplinary research area combining elements from modern physics and chemistry, materials science and molecular biology. Nanotechnology includes the integration of these nanoscale objects into larger functional material components and systems, with at least one characteristic dimension measured in the nanometre range [13].
Various applications of nanostructured materials are schematically shown in Figure 1.1. The past few decades have seen a significant increase in studies of nanoscale systems with a huge emphasis on controlled synthesis of new nanoparticles with different sizes and shapes and in-depth understanding of their chemical and physical properties [14]. There is a wide range of techniques explored for producing different kinds of nanoparticles. Generally, two strategies are used in synthesis of nanoparticulate systems, referred to as “top-down” and “bottom-up” approaches or strategies. In the top-down approach large particles are used as starting materials and using appropriate techniques they are broken down into smaller particles of nanoscale dimensions. In the bottom-up approach, smaller particles, typically ions or molecules are used as precursors to grow larger particles, restricted to nanoscale dimensions [2,5]. Broadly these approaches essentially utilize three processes: (i) condensation from vapour, (ii) chemical reactions, and (iii) solid-state processing such as milling [15]. The nanoparticulate preparation methods could be classified into two categories; physical and chemical methods. In the physical methods, evaporation or laser abrasion from bulk samples, such as solid metal blocks, is typically utilized to generate nanoparticles. These methods include annealing techniques and vacuum and gas-phase techniques such as atomic layer deposition (ALD), chemical vapour deposition (CVD), and molecular beam epitaxy (MBE) [16-21]. ALD is a well- established crystallization technique for growing thin-films. It is based on chemical reactions at a heated surface of a solid substrate, to which the …

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TABLE OF CONTENTS :

  • DECLARATION
  • SUMMARY
  • LIST OF PUBLICATIONS
  • ACKNOWLEDGEMENTS
  • SYMBOLS, ABBREVIATIONS AND NOMENCLATURE
  • CHAPTER I General Introduction
    • 1.1. Nanoscale materials
    • 1.2. Overview of catalysis and electrocatalysis involving nanoscale materials of noble metals
      • 1.2.1. Noble metals
      • 1.2.2. Catalysis: General concepts
      • 1.2.3. Multimetallic catalysts
      • 1.2.4. Electrocatalysis
      • 1.2.5. Electrocatalysts in fuel cells
      • 1.2.5. Electrocatalysts in electroanalysis
    • 1.3. Advances in electrochemical synthetic methods of nanoparticulate noble metals
    • 1.4. Thesis context and theme
      • 1.4.1. Thesis outline
  • CHAPTER II Characterisation of Electrodes and Electrochemical Processes: An Overview of Concepts, Techniques and Practical Aspects
    • 2.1. Introduction
    • 2.2. Electrochemical methods
      • 2.2.1. Electrochemical cells
      • 2.2.1.1. Equilibrium Electrochemistry
      • 2.2.1.2. Dynamic Electrochemistry
      • 2.2.1.3. Charge transfer resistance
      • 2.2.1.4. Mass transport effects
      • 2.2.2. Electric double layer, inner-sphere and outer-sphere electrode reactions
      • 2.2.3. Potential step and sweep techniques
        • 2.2.3.1. Chronoamperometry
        • 2.2.3.2. Chronocoulometry
        • 2.2.3.3. Voltammetry
        • 2.2.3.3.1. Linear sweep voltammetry
        • 2.2.3.3.2. Cyclic voltammetry
      • 2.2.3.4. Hydrodynamic voltammetry
        • 2.2.3.5. Voltammetry of inner-sphere electrode reactions
        • 2.2.3.5.1. Surface electrochemistry
        • 2.2.3.5.2. Surface area
        • 2.2.3.5.3. Voltammetry and electrocatalysis
        • 2.2.3.6. Anodic stripping voltammetry
      • 2.2.3.6.1. Electrochemically-active surface area
    • 2.2.4. Electrochemical impedance spectroscopy
    • 2.2.4.1. Equivalent circuits and electrochemical cells
    • 2.3. Techniques for compositional, structural and morphological characterisation
    • 2.3.1. Electron microscopy
    • 2.3.2. Scanning Probe Microscopy
    • 2.3.3. Energy-dispersive X–ray spectroscopy
    • 2.3.4. X-ray photoelectron spectroscopy
    • 2.3.5. X–ray diffraction
    • 2.4. Summary
  • CHAPTER III Automated Sequential Electrodeposition, Surface-Limited Redox-Replacement Reactions and Electrocatalysis: Nanostructured Electrodes of Platinum and Ruthenium on Glassy Carbon
    • 3.1. Introduction
    • 3.2. Experimental details
    • 3.2.1. Instrumentation and apparatus
      • 3.2.1.1. Electrochemical flow-cells
      • 3.2.2. Electrochemical deposition: Modelling and experimental procedures
      • 3.2.2.1. Electrochemical potential and pH: Thermodynamic modelling
      • 3.3.2.2. Materials and electrolyte solutions
      • 3.3.2.3. Pre-treatment of working electrode and deposition substrate: glassy carbon
    • 3.3.2.4. Pre-treatment of reference and counter electrodes
    • 3.3.2.5. Electrosynthesis of monometallic multilayered platinum on glassy carbon
    • 3.3.2.6. Electrosynthesis of bimetallic multilayered systems of platinum and ruthenium on glassy carbon
      • 3.3.2.6.1. Sequential surface-limited redox-replacement reactions involving copper
      • 3.3.2.6.2. Sequential spontaneous deposition
      • 3.3.2.6.3. Sequential codeposition
      • 3.3.3. Physico-chemical and analytical characterization experiments
    • 3.3.3.1. Microscopic and spectroscopic analyses
    • 3.3.3.2. Analytical electrochemistry
    • 3.3.4. Electrocatalysis: characterization experiments
    • 3.3.4.1. Methanol oxidation reaction
    • 3.3.4.2. Oxygen reduction reaction
    • 3.4. Results and discussion
    • 3.4.1. Effects of electrochemical deposition potential and pH on Pt–Cu–H2O and Ru–Cu–H2O systems: Thermodynamic considerations
    • 3.4.2. Electrodeposition of templating Cu on glassy carbon
    • 3.4.3. Sequential electrodeposition: characteristics of surface-limited redox replacement of copper by platinum and ruthenium
    • 3.4.4. Effects of templating copper adlayers: spontaneous deposition of platinum and ruthenium
    • 3.4.5. Sequential codeposition of platinum and ruthenium
    • 3.4.6. Microscopy and energy-dispersive X-ray spectroscopy
    • 3.4.7. Electrochemistry of platinum and ruthenium nanostructured multilayered electrode systems on glassy carbon
    • 3.4.7.1. Surface electrochemistry
    • 3.4.7.2. Outer-sphere electrochemical activity
    • 3.4.7.3. Inner-sphere electrochemical activity
    • 3.4.8. Electrocatalytic reactions on multilayered platinum-containing electrode systems
    • 3.4.8.1. Methanol oxidation reaction
    • 3.4.8.2. Oxygen Reduction Reaction
    • 3.5. Summary
  • CHAPTER IV Electrochemical Deposition and Electrocatalytic Properties of Multilayered Nanoclusters of Platinum and Gold
    • 4.1. Introduction
    • 4.2. Experimental Details
    • 4.2.1. Materials
    • 4.2.2. Electrodeposition
    • 4.2.3. Thermodynamic Modelling
    • 4.2.3 Electrochemical Characterization
    • 4.2.4 Surface and Bulk Characterization
    • 4.3. Results and Discussion
    • 4.3.1. Current–Potential–Time Variations and Thermodynamic Modelling
    • 4.3.2. Microscopic Analysis
    • 4.3.3. Surface Electrochemistry
    • 4.3.4. Surface and Bulk Properties
      • 4.3.4.1. Electrochemically-Active Surface Area
      • 4.3.4.2. ICP- MS Analysis
      • 4.3.4.3. XPS Analysis
    • 4.3.5. Electrocatalysis of Formic Acid Oxidation Reaction and Carbon Monoxide Adsorption-Oxidation Process
    • 4.3.5.1. Voltammetric Studies
    • 4.3.5.2. Electrochemical Impedance Spectroscopy
    • 4.4. Summary
  • CHAPTER V Kinetics and Thermodynamics of Phase Formation via Surface-Limited Reactions in Electrosynthesis of Multilayered Platinum on Gold
    • 5.1. Introduction
    • 5.2. Experimental Details
    • 5.2.1. Materials
    • 5.2.2. Electrochemical deposition
    • 5.2.3. Physical characterization
    • 5.3. Theoretical basis
    • 5.4. Results and discussion
    • 5.4.1. Characteristics of the Aufilm substrate and thermodynamics of surface coverage by UPD of Cu
    • 5.4.2. Physico–chemical analysis of deposition processes of the multilayered n(Pt)Cu/Aufilm electrode system
    • 5.4.3. Modelling adlayer phase formation during SLRRPt
    • 5.4.4. Gibbs free energy variations during successive SLRR reactions
    • 5.5. Summary
  • CHAPTER VI Conclusions and Perspectives
    • 6.1. Introduction
    • 6.2. Main deductions and general conclusions
    • 6.3. Perspectives
    • 6.4. Recommendations
    • REFERENCES

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