Modern Electrochemistry Volume 1: An Introduction to an Interdisciplinary Area

This book had its nucleus in some lectures given by one of us (J. O'M. B. ) in a course on electrochemistry to students of energy conversion at the University of Pennsylvania. It was there that he met a number of people trained in chemistry, physics, biology, metallurgy, and materials science, all of whom wanted to know something about electrochemistry. The concept of writing a book about electrochemistry which could be understood by people with very varied backgrounds was thereby engendered. The lectures were recorded and written up by Dr. Klaus Muller as a 293-page manuscript. At a later stage, A. K. N. R. joined the effort; it was decided to make a fresh start and to write a much more comprehensive text. Of methods for direct energy conversion, the electrochemical one is the most advanced and seems the most likely to become of considerable practical importance. Thus, conversion to electrochemically powered trans­ portation systems appears to be an important step by means of which the difficulties of air pollution and the effects of an increasing concentration in the atmosphere of carbon dioxide may be met. Corrosion is recognized as having an electrochemical basis. The synthesis of nylon now contains an important electrochemical stage. Some central biological mechanisms have been shown to take place by means of electrochemical reactions. A number of American organizations have recently recommended greatly increased activity in training and research in electrochemistry at universities in the United States.

1 Electrochemistry.- 1.1 Introduction.- 1.2 Electrons at and across Interfaces.- 1.2.1 Many Properties of Materials Depend upon Events Occurring at Their Surfaces.- 1.2.2 Almost All Interfaces Are Electrified.- 1.2.3 The Continuous Flow of Electrons across an Interface: Electrochemical Reactions.- 1.2.4 Electrochemical and Chemical Reactions.- 1.3 Basic Electrochemistry.- 1.3.1 Electrochemistry before 1950.- 1.3.2 The Treatment of Interfacial Electron Transfer as a Rate Process: The 1950’s.- 1.3.3 Quantum Electrochemistry: The 1960’s.- 1.3.4 Ions in Solution, as well as Electron Transfer across Interfaces.- 1.4 The Relation of Electrochemistry to Other Sciences.- 1.4.1 Some Diagrammatic Presentations.- 1.4.2 Some Examples of the Involvement of Electrochemistry in Other Sciences.- 1.4.3 Electrochemistry as an Interdisciplinary Field, Apart from Chemistry?.- 1.5 Electrodics and Electronics.- 1.6 Transients.- 1.7 Electrodes are Catalysts.- 1.8 The Electromagnetic Theory of Light and the Examination of Electrode Surfaces.- 1.9 Science, Technology, Electrochemistry, and Time.- 1.9.1 Do Interfacial Charge-Transfer Reactions Have a Wider Significance Than Has Hitherto Been Realized?.- 1.9.2 The Relation between Three Major Advances in Science, and the Place of Electrochemistry in the Developing World.- 2 Ion-Solvent Interactions.- 2.1 Introduction.- 2.2 The Nonstructural Treatment of Ion-Solvent Interactions.- 2.2.1 A Quantitative Measure of Ion-Solvent Interactions.- 2.2.2 The Born Model: A Charged Sphere in a Continuum.- 2.2.3 The Electrostatic Potential at the Surface of a Charged Sphere.- 2.2.4 On the Electrostatics of Charging (or Discharging) Spheres.- 2.2.5 The Born Expression for the Free Energy of Ion-Solvent Interactions.- 2.2.6 The Enthalpy and Entropy of Ion-Solvent Interactions.- 2.2.7 Can One Experimentally Study the Interactions of a Single Ionic Species with the Solvent?.- 2.2.8 The Experimental Evaluation of the Heat of Interaction of a Salt and Solvent.- 2.2.9 How Good Is the Born Theory?.- Further Reading.- 2.3 Structural Treatment of the Ion-Solvent Interactions.- 2.3.1 The Structure of the Most Common Solvent, Water.- 2.3.2 The Structure of Water near an Ion.- 2.3.3 The Ion-Dipole Model of Ion-Solvent Interactions.- 2.3.4 Evaluation of the Terms in the Ion-Dipole Approach to the Heat of Solvation.- 2.3.5 How Good Is the Ion-Dipole Theory of Solvation?.- 2.3.6 The Relative Heats of Solvation of Ions on the Hydrogen Scale.- 2.3.7 Do Oppositely Charged Ions of Equal Radii Have Equal Heats of Solvation?.- 2.3.8 The Water Molecule Can Be Viewed as an Electrical Quadrupole.- 2.3.9 The Ion-Quadrupole Model of Ion-Solvent Interactions.- 2.3.10 Ion-Induced-Dipole Interactions in the Primary Solvation Sheath.- 2.3.11 How Good Is the Ion-Quadrupole Theory of Solvation?.- 2.3.12 The Special Case of Interactions of the Transition-Metal Ions with Water.- 2.3.13 Some Summarizing Remarks on the Energetics of Ion-Solvent Interactions.- Further Reading.- 2.4 The Solvation Number.- 2.4.1 How Many Water Molecules Are Involved in the Solvation of an Ion?.- 2.4.2 Static and Dynamic Pictures of the Ion-Solvent Molecule Interaction.- 2.4.3 The Meaning of Hydration Numbers.- 2.4.4 Why Is the Concept of Solvation Numbers Useful?.- 2.4.5 On the Determination of Solvation Numbers.- Further Reading.- 2.5 The Dielectric Constant of Water and Ionic Solutions.- 2.5.1 An Externally Applied Electric Field Is Opposed by Counterfields Developed within the Medium.- 2.5.2 The Relation between the Dielectric Constant and Internal Counterfields.- 2.5.3 The Average Dipole Moment of a Gas-Phase Dipole Subject to Electrical and Thermal Forces.- 2.5.4 The Debye Equation for the Dielectric Constant of a Gas of Dipoles.- 2.5.5 How the Short-Range Interactions between Dipoles Affect the Average Effective Moment of the Polar Entity Which Responds to an External Field.- 2.5.6 The Local Electric Field in a Condensed Polar Dielectric.- 2.5.7 The Dielectric Constant of Liquids Containing Associated Dipoles.- 2.5.8 The Influence of Ionic Solvation on the Dielectric Constant of Solutions.- Further Reading.- 2.6 Ion-Solvent-Nonelectrolyte Interactions.- 2.6.1 The Problem.- 2.6.2 The Change in Solubility of a Nonelectrolyte Due to Primary Solvation.- 2.6.3 The Change in Solubility Due to Secondary Solvation.- 2.6.4 The Net Effect on Solubility of Influences from Primary and Secondary Solvation.- 2.6.5 The Case of Anomalous Salting in.- Further Reading.- Appendix 2.1 Free Energy Change and Work.- Appendix 2.2 The Interaction between an Ion and a Dipole.- Appendix 2.3 The Interaction between an Ion and a Water Quadrupole.- 3 Ion-Ion Interactions.- 3.1 Introduction.- 3.2 True and Potential Electrolytes.- 3.2.1 Ionic Crystals Are True Electrolytes.- 3.2.2 Potential Electrolytes: Nonionic Substances Which React with the Solvent to Yield Ions.- 3.2.3 An Obsolete Classification: Strong and Weak Electrolytes.- 3.2.4 The Nature of the Electrolyte and the Relevance of Ion-Ion Interactions.- Further Reading.- 3.3 The Debye-Hückel (or Ion-Cloud) Theory of Ion-Ion Interactions.- 3.3.1 A Strategy for a Quantitative Understanding of Ion-Ion Interactions.- 3.3.2 A Prelude to the Ionic-Cloud Theory.- 3.3.3 How the Charge Density near the Central Ion Is Determined by Electrostatics: Poisson’s Equation.- 3.3.4 How the Excess Charge Density near the Central Ion Is Given by a Classical Law for the Distribution of Point Charges in a Coulombic Field.- 3.3.5 A Vital Step in the Debye-Hückel Theory of the Charge Distribution around Ions: Linearization of the Boltzmann Equation.- 3.3.6 The Linearized Poisson-Boltzmann Equation.- 3.3.7 The Solution of the Linearized P-B Equation.- 3.3.8 The Ionic Cloud around a Central Ion.- 3.3.9 How Much Does the Ionic Cloud Contribute to the Electrostatic Potential ?r at a Distance r from the Central Ion?.- 3.3.10 The Ionic Cloud and the Chemical-Potential Change Arising from IonIon Interactions.- Further Reading.- 3.4 Activity Coefficients and Ion-Ion Interactions.- 3.4.1 The Evolution of the Concept of Activity Coefficient.- 3.4.2 The Physical Significance of Activity Coefficients.- 3.4.3 The Activity Coefficient of a Single Ionic Species Cannot Be Measured.- 3.4.4 The Mean Ionic Activity Coefficient.- 3.4.5 The Conversion of Theoretical Activity-Coefficient Expressions into a Testable Form.- Further Reading.- 3.5 The Triumphs and Limitations of the Debye-Hückel Theory of Activity Coefficients.- 3.5.1 How Well Does the Debye-Hückel Theoretical Expression for Activity Coefficients Predict Experimental Values?.- 3.5.2 Ions Are of Finite Size, Not Point Charges.- 3.5.3 The Theoretical Mean Ionic-Activity Coefficient in the Case of Ionic Clouds with Finite-Sized Ions.- 3.5.4 The Ion-Size Parameter a.- 3.5.5 Comparison of the Finite-Ion-Size Model with Experiment.- 3.5.6 The Debye-Hückel Theory of Ionic Solutions: An Assessment.- 3.5.7 On the Parentage of the Theory of Ion-Ion Interactions.- Further Reading.- 3.6 Ion-Solvent Interactions and the Activity Coefficient.- 3.6.1 The Effect of Water Bound to Ions on the Theory of Deviations from Ideality.- 3.6.2 Quantitative Theory of the Activity of an Electrolyte as a Function of the Hydration Number.- 3.6.3 The Water-Removal Theory of Activity Coefficients and Its Apparent Consistency with Experiment at High Electrolytic Concentrations.- Further Reading.- 3.7 The So-Called “Rigorous” Solutions of the Poisson-Boltzmann Equation.- Further Reading.- 3.8 Temporary Ion Association in an Electrolytic Solution: Formation of Pairs, Triplets, etc..- 3.8.1 Positive and Negative Ions Can Stick Together: Ion-Pair Formation.- 3.8.2 The Probability of Finding Oppositely Charged Ions near Each Other.- 3.8.3 The Fraction of Ion Pairs, According to Bjerrum.- 3.8.4 The Ion-Association Constant KA of Bjerrum.- 3.8.5 Activity Coefficients, Bjerrum’s Ion Pairs, and Debye’s Free Ions.- 3.8.6 The Fuoss Approach to Ion-Pair Formation.- 3.8.7 From Ion Pairs to