Electrosorption

ISBN-13: 9781468417333 / Angielski / Miękka / 2012 / 222 str.

Eliezer Gileadi

Opis

The gradual emergence during the last decade of the study of the mechanism of electrode reactions from the dark ages has given stimulus to a consideration of the double layer at metal-solution interfaces, which extends far outside the classical experimental studies of the capacitance of the mercury solution interface made during the 1950's by D. C. Grahame at Amherst College, Massachusetts. The central aspect of the study of an electrode reaction is the elucidation of its path and rate-determining step. Two fields are, however, prerequisites for such studies. First, it must be known what species are in the bulk of the solution, for these will seldom be simple ones such as H30 and this study ("complex ions") has been made with both extent and depth. Second, the occupancy of the surface of the electrocatalyst and the associated field gradients must be known as a function of position in the double layer. Such "maps of the double layer" can be given with reasonable certainty up to concentrations of about 1 N for mercury in contact with solutions of inorganic ions. However, this is-or was until very recently-the extent of the know ledge. The problems confronting a fundamental approach to the rational development of, e.g., fuel cell catalysis were therefore considerable."

Spis treści

I Adsorption in Electrochemistry.- 1. Introduction.- 1.1. Special Aspects of Adsorption from Solution.- 2. Equations of State and Isotherms.- 2.1. Definitions and Use.- 2.2. Conversion of Equation of State to Isotherms.- 3. The Langmuir Isotherm.- 3.1. Value and Deficiency.- 3.2. Methods of Derivation.- 3.3. Langmuir-like Adsorption.- 3.3.1. Adsorption of Large Molecules.- 3.3.2. Adsorption from a Second Layer.- 3.4. Langmuir Adsorption from Solution.- 4. The Temkin Isotherm.- 4.1. Assumptions, General Form, and Limiting Cases.- 5. The Frumkin Isotherm.- 5.1. Free Energy of Adsorption Decreasing with Coverage.- 5.2. Free Energy of Adsorption Increasing with Coverage.- 5.3. Frumkin-Type Adsorption from Solution.- 6. Experimental Tests of the Isotherms.- 7. Conclusions.- References.- 2 Organic Adsorption at Electrodes.- 1. Introduction.- 2. Comparison of Methods for Adsorption Studies in the Gas Phase and at Electrodes in Solution.- 3. Energetics of Adsorption.- 4. Trends in Electrosorption.- 5. Modes of Adsorption and Structure of Adsorbed Species.- 6. The Adsorption Characteristics of Some Selected Compounds.- 6.1. Carbon Monoxide.- 6.2. Formic Acid.- 6.3. Alcohols.- 6.4. Hydrocarbons.- 7. Open-Circuit Adsorption Behavior.- 8. Summary.- References.- 3 Kinetics of Diffusion-Controlled Electrosorption of Neutral Molecules.- 1 Introduction.- 2. The Adsorption Isotherm and the Mass Transfer Process.- 3. Analysis of the Diffusion Problem.- 4. The Time Variation of the Surface Concentration of Adsorbed Species.- 5. Mass Transport-Controlled Electrosorption Under Stirred Conditions.- References.- 4 Oxygen Adsorption and Oxide Formation on Electrodes.- 1. Introduction.- 2. Thermodynamics of Oxidation.- 3. Characteristics of Physically Adsorbed Oxygen.- 4. Characteristics of Chemisorbed Oxygen.- 5. The Occurrence of Physical Adsorption.- 6. The Occurrence of Chemisorption.- 7. Mechanism of Oxide Growth.- 7.1. Growth of Nonconducting Oxides.- 7.2. Growth of Semiconducting Oxides.- 7.3. Growth of Conducting Oxides.- 7.4. Growth of Oxides by Diffusion.- 8. Why is Adsorbed Oxygen Important ?.- References.- 5 The Potential of Zero Charge.- 1. Introduction.- 1.1. What is the Potential of Zero Charge ?.- 1.2. The Rational Scale of Potential.- 1.3. Electrode Kinetics and the Potential of Zero Charge.- 1.3.1. Primary Effects.- 1.3.2. Secondary Effects.- 1.4. Dependence of Adsorption on the Potential of Zero Charge.- 2. Aspects of the Potential of Zero Charge Dependent on the Metal.- 2.1. The Relation Between Potential of Zero Charge, Contact Potential Difference, and Work Function.- 2.2. Physicochemical Properties of the Metal.- 3. Aspects of the Potential of Zero Charge Related to the System.- 3.1. Specific Adsorption of Ions.- 3.2. Organic Adsorption.- 3.3. Surface Coverage with Atomic Hydrogen or Oxygen.- 3.4. pH Variation.- 4. Methods of Determination of the Potential of Zero Charge.- 4.1. Surface Tension Methods.- 4.1.1. Electrocapillary Curves.- 4.1.2. Contact Angle Method.- 4.2. Change of Surface Area.- 4.3. Capacity Measurements.- 4.4. Adsorption Methods.- 4.4.1. Ionic Adsorption.- 4.4.2. Dependence of Organic Adsorption on Electrolyte Concentration.- 4.5. Friction Methods.- 4.5.1. The Pendulum Method.- 4.5.2. The Angle of Inclination Method.- 4.6. Ultrasonic Method.- 4.7. Repulsion of Double Layers on Two Wires.- 5. Conclusions.- References.- 6 The Role of Solvents at Electrodes.- 1. Introduction.- 2. Field-Dependent Orientation of the Solvent at the Metal—Solution Interface.- 3. Dielectric Properties of the Solvent at the Electrode.- 3.1. The Double Layer as Parallel Plate Capacitor.- 3.2. Dielectric Properties of Dipolar Substances.- 3.3. Dielectric Relaxation and Rate Theory; Distribution of Relaxation Times.- 3.4. Experimental Determination of the Dielectric Properties of Water in the Electric Double Layer.- 3.5. Theoretical Considerations and Discussions.- 3.5.1. Artifacts.- 3.5.2. The Value of the Mean Relaxation Time.- 3.5.3. Dipole Relaxation and Double-Layer Structure.- 3.5.4. The Value of ?x and the Mechanism of Conduction.- 3.6. Conclusions.- 4. Adsorptive Properties of the Solvent at the Electrode.- 4.1. Gibbs Surface Excess and Adsorption of Neutral Molecules.- 4.2. Model of the Adsorption Process.- 4.2.1. Exchange Equilibrium.- 4.2.2. The Mechanism of Adsorption.- 4.2.3. Model of Adsorbed Molecules.- 4.2.4. Molecular Interactions at the Interface.- 4.3. The Electric Variable.- 4.4. Adsorption Equations.- 4.5. Conclusions.- 5. Final Remarks.- References.- 7 Theoretical Consideration of the Double Layer.- 1. An Electrostatic Model of the Electrochemical Double Layer.- 1.1. General Features of the Model.- 1.2. Distinction Between the Electrostatic Interactions in the Double Layer.- 1.3. A Closed Solution for the Coulomb Potential of an Isolated Charge.- 1.4. Determination of the Average Electrostatic Potential in the Double Layer.- 2. The Local Thermodynamic Formulation for Inhomogeneous Electrochemical Systems.- 2.1. The Local Balance Theory of Prigogine, Mazur, and Defay.- 2.2. The Definition of Pressure at the Interphase.- 2.3. The Definition of the Electrochemical Potential.- 2.4. The Distribution Function at Equilibrium.- 3. Theories of the Ionic Double Layer.- 3.1. General Evolution of the Theoretical Concepts of the Diffuse Layer.- 3.2. Preliminaries on the Statistical Mechanical Formulation in Fluids.- 3.2.1. The Set Notation.- 3.2.2. Definition of Probability Density in the Canonical Ensemble.- 3.2.3. The Correlation and Radial Distribution Function.- 3.2.4. Kirkwood’s Superposition Approximation.- 3.2.5. Distribution in the Grand Ensemble.- 3.2.6. Average Electrostatic Potential and Free Energy.- 3.3. The Differential Equation Method of Debye and Hückel.- 3.4. The Gouy Potential in the Diffuse Layer.- 3.4.1. The Integrability Condition in the Case of an Inhomogeneous System.- 3.4.2. The Solution of Gouy and Chapman.- 3.4.3. Determination of the Self-Atmosphere Effect by Means of the Cluster Expansion Method.- 3.4.4. The Diffuse Layer Version of the Expansion Method in Terms of a Charging Parameter.- 3.4.5. The Evaluation of the Electrostatic Potentials in the Diffuse Layer by Means of Stillinger and Kirkwood’s Method.- 3.4.6. Application of the Local Thermodynamic Method.- 3.5. General Evolution of Ideas on Specific Adsorption in the Inner Layer.- 3.6. General Expression of the Adsorption Isotherm.- 3.7. The Mobile Monolayer Adsorption.- 3.7.1. Description of the Model of Mobile Adsorption.- 3.7.2. The Cavity Field.- 3.7.3. The Coordination Field.- 3.7.4. The Radial Redistribution Work.- 3.7.5. The Final Form of the Adsorption Isotherm and Its Application.- 3.8. The Discreteness of Charge Model and Lattice Adsorption.- References.