Modern Aspects of Electrochemistry No. 7, Softcover reprint of the original 1st ed. 1972

Despite reductions in the level of research activity in most fields which, for reasons of economic decline, have taken place in the U.S. during the last year or two, world progress in the fundamental aspects has continued actively. An important aspect of such recent work has been the use of nonaqueous solvents in studies on the constitution of the double-layer and electrochemical reactions. Interpretation of the behavior of electrode interfaces in such solvents demands more knowledge of the solvation properties of ions in nonaqueous media. Chapter 1 by Pad ova on "Ionic Solvation in Nonaqueous and Mixed Solvents" gives an up to date review of the present state of knowledge in this field, together with tabulations of data that are likely to be of quantitative value in further investigations of both homogeneous and heterogeneous electrochemistry in such media. Electrochemical studies of cathodic processes in nonaqueous solvents have, in recent years, revealed the role of solvated electrons. These are of interest in new approaches to reductive electro-organic synthesis. Similarly, the generation of hydrated electrons in photo­ cathodic processes is of great interest. In Chapter 2, by Conway, the conditions under which solvated electrons can arise in electrode processes are critically examined and the electro-organic reactions that hwe been investigated are reviewed. The supposed electro­ generation of hydrated electrons in the water solvent and as inter­ mediates in cathodic hydrogen evolution is shown to be unlikely.

1 Ionic Solvation in Nonaqueous and Mixed Solvents.- I. Introduction.- II. Thermodynamics of Solvation.- III. Determination of Thermodynamics of Solvation.- 1. Heats of Solvation.- 2. Free Energies of Solvation.- 3. Entropies of Solvation.- IV. Theoretical Aspects of Solvation.- 1. Real Free Energy of Solvation.- 2. Electrostatic Theory of Solvation.- 3. Thermodynamics of a Dielectric Continuum.- 4. Structural Approaches.- V. Solvation Numbers.- VI. Mixed Solvents.- 1. Structural Changes in Mixed Solvents.- 2. Solvation Approach to Mixed Solvents.- 3. Thermodynamic Approach to Selective Solvation in Mixed Solvents.- 4. NMR Aspects of Solvation.- VII. Transport Processes.- 1. Viscosity.- 2. Conductance.- 3. Stokes’ Law and Walden’s Rule.- 4. Association.- References.- 2 Solvated Electrons in Field- and Photo-Assisted Processes at Electrodes.- I. Introduction.- II. Energetic Factors.- 1. Effective Work Function for Production of Solvated Electrons.- 2. Comparison of Energetics of Ion/Electrode and Electron Injection Processes.- 3. Standard Electrode Potentials for e-s: Liquid Ammonia and Water.- 4. Energy Conditions for Production of Electrons in Water.- 5. State of Solvated Electrons in Polar Media.- III. Photoassisted Electron Injection from Cathodes.- 1. Introduction.- 2. Energetic Conditions for Photoelectrochemical Emission.- 3. Experimental Characterization of the Electrochemical Photoeffect.- 4. Effects of Double-Layer Structure.- IV. Scavenger Behavior in the Electrochemical Photoeffect.- V. Chemical Evidence for Direct Cathodic Injection of Electrons into Solvents.- VI. Hydrated Electrons in Aqueous Electrochemical Reactions.- 1. Some General Problems.- 2. Standard Potential for e-aq and the Nonequilibrium Situation Arising from Annihilation Processes.- 3. Illumination Effects and Reflectance.- 4. Solvated Electrons and Organic Electrochemical Reactions.- Acknowledgment.- References.- 3 Critical Observations on the Measurement of Adsorption at Electrodes.- I. Introduction.- 1. Nature and Scope of the Discussion.- 2. Definition of “Adsorption”.- 3. Inferences about Adsorption from Observable Phenomena.- 4. Adsorption of Inorganic Species.- 5. Chemisorbed Films.- 6. Electrochemical Transformations Involving Adsorbed Reactants.- II. Direct Methods of Measuring Adsorption.- 1. Depletion of the Solution.- 2. Accumulation on the Electrode: Measurements Made after Removal from Solution.- 3. Accumulation on the Electrode: Measurements in situ.- 4. Optical Observation of the Surface Layer in situ.- III. Measurement of Surface Tension, Charge, and Capacity.- 1. Thermodynamic Theory.- 2. Measurement of Surface Tension.- 3. Measurement of Charge on the Electrode.- 4. Measurement of Double-Layer Capacity.- 5. Measurement of Tensammetric Processes.- IV. Adsorption Indicated by Effects Exerted on Faradaic Processes.- V. Summary.- Acknowledgment.- References.- 4 Transport-Controlled Deposition and Dissolution of Metals.- I. Phenomena Involved.- II. Amplification of Surface Irregularities.- III. Appearance and Growth of Dendritic Deposits.- 1. Conditions of Appearance and Factors Determining Frequency of Incidence and Rate of Growth of Dendrites.- 2. General Theory of the Appearance and Growth of Dendrites.- 3. Comparison with Results of Experiments.- 4. The Effect of the Crystal Structure of the Depositing Metal on the Direction of Growth and Shape of Dendrites.- IV. Growth of Whiskers.- 1. Introduction.- 2. Theory of Whisker Growth.- V. Formation of Powdered Deposits.- 1. Common Features.- 2. Critical Current Density of Powder Formation and Limiting Current Density of Metal Deposition.- 3. Interpretation of the Role of Transport Control in Powder Formation.- VI. Leveling.- 1. Basic Facts.- 2. Model of Leveling.- 3. Quantitative Treatment.- VII. Electropolishing.- 1. Summary of Experimental Facts.- 2. Proposed Models of Electropolishing.- 3. Quantitative Treatment of Diffusion-Controlled Smoothing.- VIII. Deposition of Metals at a Periodically Changing Rate.- 1. Reversing Currents.- 2. DC with Superimposed AC.- 3. Pulsating Currents.- 4. Theory of the Effect of Pulsating Electrolysis on the Morphology of the Deposit.- IX. Generalized Model of Transport-Controlled Processes and Approaches to Quantitative Analysis of Its Consequences.- 1. Qualitative Consideration of the Development of the Diffusion Layer.- 2. Quantitative Aspects.- 3. Some Approaches to Quantitative Solutions.- References.- 5 Mechanisms of Stepwise Electrode Processes on Amalgams.- I. Introduction.- II. Brief Historical Survey.- III. Processes with a Single Limiting Step.- 1. Rate Equations with Allowance for the ?1 Potential.- 2. Rate Equations in the Case of an Excess of Supporting Electrolyte.- 3. Principal Features of Stepwise Mechanisms.- 4. Conditions for the Accumulation of Ionic Intermediates in Solution.- 5. Combined Use of Electrochemical and Radiotracer Measurements.- 6. Experimental Data for Zinc and Indium Amalgams.- 7. Experimental Data for Other Systems.- 8. Causes of the Relative Slowness of the Last Charge-Transfer Step.- IV. Processes with Comparable Rate Constants for Successive Steps.- 1. Rate Equations for the Process with One-Electron Steps.- 2. Equations for the Partial Anodic Current.- 3. Conditions for the Applicability of the “Break” Criterion.- 4. Process Involving Higher-Order Reactions.- 5. Summary of Various Criteria for Stepwise Mechanisms.- 6. Experimental Results for Bismuth and Copper Amalgams.- 7. Experimental Results for Other Systems.- V. Application of the Criteria for Stepwise Mechanisms in Some Electrode Redox Reactions.- References.