Bockris / Reddy / Gamboa-Aldeco Modern Electrochemistry 2A

Fundamentals of Electrodics
2. Auflage 2000
ISBN: 978-0-306-47605-1
Verlag: Springer
Format: PDF
Kopierschutz: 1 - PDF Watermark

E-Book, Englisch, 812 Seiten

This text explains the subject of electrochemistry in clear, straightforward language for undergraduates and mature scientists who want to understand solutions at the molecular level. It takes full advantage of the advances in microscopy, computing power, and industrial applications in the quarter-century since the publication of the first edition. Such new techniques include scanning-tunnelling microscopy, which enables us to see atoms on electrodes, new computers capable of molecular dynamics calculations that are used in arriving at experimental values, and new room-temperature molten salts that make possible the long-postponed introduction of commercial electric cars.

The advances in electrochemistry have necessitated a thorough rewriting of volume 2, which starts with two chapters that have been thoroughly revamped from the first edition. Transients, the electrochemical approach to measurement, have been given a whole chapter to themselves. The contributions of quantum chemists to electrochemistry have resulted in a new chapter on quantum-oriented electrochemistry, which is followed by new chapters on photoelectrochemistry, organoelectrochemistry, and environmental electrochemistry.

Finally, the chapter on energy conversion and storage reflects the many advances in that technology. A completely new feature is the liberal supply of problem sets that give students the opportunity to reinforce the knowledge introduced in each chapter. Problem types represent three levels of difficulty: exercises for practice in the use of equations, somewhat more involved problems that relate the material to "real-life" situations, and more difficult "micro-research" problems, each of which may take around a day to solve.

Autoren/Hrsg.

Bockris, John O'M.

Reddy, Amulya K. N.

Gamboa-Aldeco, Maria E.

Inhaltsverzeichnis

1;PREFACE TO THE FIRST EDITION;7
2;PREFACE TO VOLUME 2A;12
2.1;TEXT REFERENCES AND READING LISTS;13
3;CONTENTS;15
4;CHAPTER 6 THE ELECTRIFIED INTERFACE;29
4.1;6.1. ELECTRIFICATION OF AN INTERFACE;29
4.1.1;6.1.1. The Electrode/Electrolyte Interface: The Basis of Electrodics;29
4.1.2;6.1.2. New Forces at the Boundary of an Electrolyte;29
4.1.3;6.1.3. The Interphase Region Has New Properties and New Structures;32
4.1.4;6.1.4. An Electrode Is Like a Giant Central Ion;32
4.1.5;6.1.5. The Consequences of Compromise Arrangements: The Electrolyte Side of the Boundary Acquires a Charge;33
4.1.6;6.1.6. Both Sides of the Interface Become Electrified: The Electrical Double Layer;33
4.1.7;6.1.7. Double Layers Are Characteristic of All Phase Boundaries;36
4.1.8;6.1.8. What Knowledge Is Required before an Electrified Interface Can Be Regarded as Understood?;36
4.1.9;6.1.9. Predicting the Interphase Properties from the Bulk Properties of the Phases;38
4.1.10;6.1.10. Why Bother about Electrified Interfaces?;38
4.2;6.2. EXPERIMENTAL TECHNIQUES USED IN STUDYING INTERFACES;40
4.2.1;6.2.1. What Type of Information Is Necessary to Gain an Understanding of Interfaces?;40
4.2.2;6.2.2. The Importance of Working with Clean Surfaces (and Systems);40
4.2.3;6.2.3. Why Use Single Crystals?;42
4.2.4;6.2.4. In Situ vs. Ex Situ Techniques;43
4.2.5;6.2.5. Ex Situ Techniques;46
4.2.6;6.2.6. In Situ Techniques;55
4.3;6.3. THE POTENTIAL DIFFERENCE ACROSS ELECTRIFIED INTERFACES;64
4.3.1;6.3.1. What Happens When One Tries to Measure the Potential Difference Across a Single Electrode/Electrolyte Interface?;64
4.3.2;6.3.2. Can One Measure Changes in the Metal–Solution Potential Difference?;69
4.3.3;6.3.3. The Extreme Cases of Ideally Nonpolarizable and Polarizable Interfaces;71
4.3.4;6.3.4. The Development of a Scale of Relative Potential Differences;73
4.3.5;6.3.5. Can One Meaningfully Analyze an Electrode–Electrolyte Potential Difference?;75
4.3.6;6.3.6. The Outer Potential of a Material Phase in a Vacuum;79
4.3.7;6.3.7. The Outer Potential Difference, between the Metal and the Solution;80
4.3.8;6.3.8. The Surface Potential, of a Material Phase in a Vacuum;81
4.3.9;6.3.9. The Dipole Potential Difference across an Electrode–Electrolyte Interface;82
4.3.10;6.3.10. The Sum of the Potential Differences Due to Charges and Dipoles: The Inner Potential Difference;84
4.3.11;6.3.11. The Outer, Surface, and Inner Potential Differences;86
4.3.12;6.3.12. Is the Inner Potential Difference an Absolute Potential Difference?;87
4.3.13;6.3.13. The Electrochemical Potential, the Total Work from Infinity to Bulk;88
4.3.14;6.3.14. The Electron Work Function, Another Interfacial Potential;92
4.3.15;6.3.15. The Absolute Electrode Potential Further Reading;95
4.4;6.4. THE ACCUMULATION AND DEPLETION OF SUBSTANCES AT AN INTERFACE;100
4.4.1;6.4.1. What Would Represent Complete Structural Information on an Electrified Interface?;100
4.4.2;6.4.2. The Concept of Surface Excess;101
4.4.3;6.4.3. Is the Surface Excess Equivalent to the Amount Adsorbed?;103
4.4.4;6.4.4. Does Knowledge of the Surface Excess Contribute to Knowledge of the Distribution of Species in the Interphase Region?;104
4.4.5;6.4.5. Is the Surface Excess Measurable?;105
4.5;6.5. THE THERMODYNAMICS OF ELECTRIFIED INTERFACES;106
4.5.1;6.5.1. The Measurement of Interfacial Tension as a Function of the Potential Difference across the Interface;106
4.5.2;6.5.2. Some Basic Facts about Electrocapillary Curves;110
4.5.3;6.5.3. Some Thermodynamic Thoughts on Electrified Interfaces;112
4.5.4;6.5.4. Interfacial Tension Varies with Applied Potential: Determination of the Charge Density on the Electrode;116
4.5.5;6.5.5. Electrode Charge Varies with Applied Potential: Determination of the Electrical Capacitance of the Interface;117
4.5.6;6.5.6. The Potential at which an Electrode Has a Zero Charge;119
4.5.7;6.5.7. Surface Tension Varies with Solution Composition: Determination of the Surface Excess;120
4.5.8;6.5.8. Summary of Electrocapillary Thermodynamics;124
4.5.9;6.5.9. Retrospect and Prospect for the Study of Electrified Interfaces Further Reading;127
4.6;6.6. THE STRUCTURE OF ELECTRIFIED INTERFACES;129
4.6.1;6.6.1. A Look into an Electrified Interface;129
4.6.2;6.6.2. The Parallel-Plate Condenser Model: The Helmholtz–Perrin Theory;131
4.6.3;6.6.3. The Double Layer in Trouble: Neither Perfect Parabolas nor Constant Capacities;134
4.6.4;6.6.4. The Ionic Cloud: The Gouy–Chapman Diffuse-Charge Model of the Double Layer;134
4.6.5;6.6.5. The Gouy–Chapman Model Provides a Potential Dependence of the Capacitance, but at What Cost?;138
4.6.6;6.6.6. Some Ions Stuck to the Electrode, Others Scattered in Thermal Disarray: The Stern Model;140
4.6.7;6.6.7. The Contribution of the Metal to the Double-Layer Structure;145
4.6.8;6.6.8. The Jellium Model of the Metal;148
4.6.9;6.6.9. How Important Is the Surface Potential for the Potential of the Double Layer?;151
4.7;6.7. STRUCTURE AT THE INTERFACE OF THE MOST COMMON SOLVENT: WATER;153
4.7.1;6.7.1. An Electrode Is Largely Covered with Adsorbed Water Molecules;153
4.7.2;6.7.2. Metal–Water Interactions;154
4.7.3;6.7.3. One Effect of the Oriented Water Molecules in the Electrode Field: Variation of the Interfacial Dielectric Constant;155
4.7.4;6.7.4. Orientation of Water Molecules on Electrodes: The Three-State Water Model;156
4.7.5;6.7.5. How Does the Population of Water Species Vary with the Potential of the Electrode?;158
4.7.6;6.7.6. The Surface Potential, Due to Water Dipoles;162
4.7.7;6.7.7. The Contribution of Adsorbed Water Dipoles to the Capacity of the Interface;168
4.7.8;6.7.8. Solvent Excess Entropy of the Interface: A Key to Obtaining Structural Information on Interfacial Water Molecules;170
4.7.9;6.7.9. If Not Solvent Molecules, What Factors Are Responsible for Variation in the Differential Capacity of the Electrified Interface with Potential?;173
4.8;6.8. IONIC ADSORPTION;177
4.8.1;6.8.1. How Close Can Hydrated Ions Come to a Hydrated Electrode?;177
4.8.2;6.8.2. What Parameters Determine if an Ion Is Able to Contact Adsorb on an Electrode?;178
4.8.3;6.8.4. Effect of the Electrical Field at the Interface on the Shape of the on an Electrode?;187
4.8.4;6.8.5. Equation of States in Two Dimensions;189
4.8.5;6.8.6. Isotherms of Adsorption in Electrochemical Systems;191
4.8.6;6.8.7. A Word about Standard States in Adsorption Isotherms;194
4.8.7;6.8.8. The Langmuir Isotherm: A Fundamental Isotherm;195
4.8.8;6.8.9. The Frumkin Isotherm: A Lateral Interaction Isotherm;196
4.8.9;6.8.10. The Temkin Isotherm: A Heterogeneous Surface Isotherm;196
4.8.10;6.8.11. The Flory–Huggins-Type Isotherm: A Substitutional Isotherm;199
4.8.11;6.8.12. Applicability of the Isotherms;199
4.8.12;6.8.13. An Ionic Isotherm for Heterogeneous Surfaces;202
4.8.13;6.8.14. Thermodynamic Analysis of the Adsorption Isotherm;213
4.8.14;6.8.15. Contact Adsorption: Its Influence on the Capacity of the Interface;217
4.8.15;6.8.16. Looking Back;221
4.9;6.9. THE ADSORPTION PROCESS OF ORGANIC MOLECULES;226
4.9.1;6.9.1. The Relevance of Organic Adsorption;226
4.9.2;6.9.2. Is Adsorption the Only Process that the Organic Molecules Can Undergo?;227
4.9.3;6.9.3. Identifying Organic Adsorption;228
4.9.4;6.9.4. Forces Involved in Organic Adsorption;229
4.9.5;6.9.5. The Parabolic Coverage–Potential Curve;230
4.9.6;6.9.6. Other Factors Influencing the Adsorption of Organic Molecules on Electrodes;236
4.10;6.10. THE STRUCTURE OF OTHER INTERFACES;242
4.10.1;6.10.1. The Structure of the Semiconductor-Electrolyte Interface;242
4.10.2;6.10.2. Colloid Chemistry;259
4.11;6.11. DOUBLE LAYERS BETWEEN PHASES MOVING RELATIVE TO EACH OTHER;264
4.11.1;6.11.1 The Phenomenology of Mobile Electrified Interfaces: Electrokinetic Properties;264
4.11.2;6.11.2. The Relative Motion of One of the Phases Constituting an Electrified Interface Produces a Streaming Current;266
4.11.3;6.11.3. A Potential Difference Applied Parallel to an Electrified Interface Produces an Electro-osmotic Motion of One of the Phases Relative to the Other;269
4.11.4;6.11.4. Electrophoresis: Moving Solid Particles in a Stationary Electrolyte;270
5;CHAPTER 7 ELECTRODICS;292
5.1;7.1. INTRODUCTION;292
5.1.1;7.1.1. Some Things One Has to Know About Interfacial Electron Transfer: It’s Both Electrical and Chemical;292
5.1.2;7.1.2. Uni-electrodes, Pairs of Electrodes in Cells and Devices;293
5.1.3;7.1.3. The Three Possible Electrochemical Devices;293
5.1.4;7.1.4. Some Special Characteristics of Electrochemical Reactions;298
5.2;7.2. ELECTRON TRANSFER UNDER AN INTERFACIAL ELECTRIC FIELD;299
5.2.1;7.2.1. A Two-Way Traffic Across the Interface: Equilibrium and the Exchange Current Density;304
5.2.2;7.2.2. The Interface Out of Equilibrium;306
5.2.3;7.2.3. A Quantitative Version of the Dependence of the Electrochemical Reaction Rate on Overpotential: The Butler–Volmer Equation;309
5.2.4;7.2.4. Polarizable and Nonpolarizable Interfaces;312
5.2.5;7.2.5. The Equilibrium State for Charge Transfer at the Metal/Solution Interface Treated Thermodynamically;314
5.2.6;7.2.6. The Equilibrium Condition: Kinetic Treatment;315
5.2.7;7.2.7. The Equilibrium Condition: Nernst’s Thermodynamic Treatment;315
5.2.8;7.2.8. The Final Nernst Equation and the Question of Signs;319
5.2.9;7.2.9. Why Is Nernst’s Equation of 1904 Still Useful?;321
5.2.10;7.2.10. Looking Back to Look Forward;322
5.3;7.3. A MORE DETAILED LOOK AT SOME QUANTITIES IN THE BUTLER–VOLMER EQUATION;324
5.3.1;7.3.1. Does the Structure of the Interphasial Region Influence the Electrochemical Kinetics There?;325
5.3.2;7.3.2. What About the Theory of the Symmetry Factor, ?;328
5.3.3;7.3.3. The Interfacial Concentrations May Depend on Ionic Transport in the Electrolyte;329
5.4;7.4. ELECTRODE KINETICS INVOLVING THE SEMICONDUCTOR/SOLUTION INTERFACE;331
5.4.1;7.4.1. Introduction;331
5.4.2;7.4.2. The Current-Potential Relation at a Semiconductor/Electrolyte Interface (Negligible Surface States);339
5.4.3;7.4.3. Effect of Surface States on Semiconductor Electrode Kinetics22;343
5.4.4;7.4.4. The Use of and Semiconductors for Thermal Reactions;343
5.4.5;7.4.5. The Limiting Current in Semiconductor Electrodes;345
5.4.6;7.4.6. Photoactivity of Semiconductor Electrodes;346
5.5;7.5. TECHNIQUES OF ELECTRODE KINETICS;348
5.5.1;7.5.1. Preparing the Solution;348
5.5.2;7.5.2. Preparing the Electrode Surface;351
5.5.3;7.5.3. Real Area;352
5.5.4;7.5.4. Microelectrodes;354
5.5.5;7.5.5. Thin-Layer Cells;360
5.5.6;7.5.6. Which Electrode System Is Best?;360
5.5.7;7.5.7. The Measurement Cell;361
5.5.8;7.5.8. Keeping the Current Uniform on an Electrode;368
5.5.9;7.5.9. Apparatus Design Arising from the Needs of the Electronic Instrumentation;369
5.5.10;7.5.10. Measuring the Electrochemical Reaction Rate as a Function of Potential (at Constant Concentration and Temperature);372
5.5.11;7.5.11. The Dependence of Electrochemical Reaction Rates on Temperature;379
5.5.12;7.5.12. Electrochemical Reaction Rates as a Function of the System Pressure;380
5.5.13;7.5.13. Impedance Spectroscopy;384
5.5.14;7.5.14. Rotating Disk Electrode;396
5.5.15;7.5.15. Spectroscopic Approaches to Electrode Kinetics;402
5.5.16;7.5.16. Ellipsometry;404
5.5.17;7.5.17. Isotopic Effects;411
5.5.18;7.5.18. Atomic-Scale Microscopy;414
5.5.19;7.5.19. Use of Computers in Electrochemistry;416
5.6;7.6. MULTISTEP REACTIONS;423
5.6.1;7.6.1. The Difference between Single-Step and Multistep Electrode;423
5.6.2;7.6.2. Terminology in Multistep Reactions;424
5.6.3;7.6.3. The Catalytic Pathway;424
5.6.4;7.6.4. The Electrochemical Desorption Pathway;425
5.6.5;7.6.5. Rate-Determining Steps in the Cathodic Hydrogen Evolution Reaction;425
5.6.6;7.6.6. Some Ideas on Queues, or Waiting Lines;426
5.6.7;7.6.7. The Overpotential Is Related to the Electron Queue at an Interface;428
5.6.8;7.6.8. A Near-Equilibrium Relation between the Current Density and Overpotential for a Multistep Reaction;429
5.6.9;7.6.9. The Concept of a Rate-Determining Step;432
5.6.10;7.6.10. Rate-Determining Steps and Energy Barriers for Multistep Reactions;437
5.6.11;7.6.11. How Many Times Must the Rate-Determining Step Take Place for the Overall Reaction to Occur Once? The Stoichiometric Number;439
5.6.12;7.6.12. The Order of an Electrodic Reaction;444
5.6.13;7.6.13. Blockage of the Electrode Surface during Charge Transfer: The Surface-Coverage Factor;447
5.7;7.7. THE INTERMEDIATE RADICAL CONCENTRATION, AND ITS EFFECT ON ELECTRODE KINETICS;450
5.7.1;7.7.1. Heat of Adsorption Independent of Coverage;450
5.7.2;7.7.2. Heat of Adsorption Dependent on Coverage;451
5.7.3;7.7.3. Frumkin and Temkin;452
5.7.4;7.7.4. Consequences from the Frumkin–Temkin Isotherm;452
5.7.5;7.7.5. When Should One Use the Frumkin–Temkin Isotherms in Kinetics Rather than the Simple Langmuir Approach?;454
5.7.6;7.7.6. Are the Electrode Kinetics Affected in Circumstances under which Varies with;454
5.8;7.8. THE REACTIVITY OF CRYSTAL PLANES OF DIFFERING ORIENTATION;458
5.8.1;7.8.1. Introduction;458
5.8.2;7.8.2. Single Crystals and Planes of Specific Orientation;458
5.8.3;7.8.3. Another Preliminary: The Voltammogram as the Arbiter of a Clean Surface;460
5.8.4;7.8.4. Examples of the Different Degrees of Reactivity Caused by Exposing Different Planes of Metal Single Crystals to the Solution;462
5.8.5;7.8.5. General Assessment of Single-Crystal Work in Electrochemistry;466
5.8.6;7.8.6. Roots of the Work on Kinetics at Single-Crystal Planes;467
5.9;7.9. TRANSPORT IN THE ELECTROLYTE EFFECTS CHARGE TRANSFER AT THE INTERFACE;468
5.9.1;7.9.1. Ionics Looks after the Material Needs of the Interface;468
5.9.2;7.9.2. How the Transport Flux Is Linked to the Charge-Transfer Flux: The Flux-Equality Condition;470
5.9.3;7.9.3. Appropriations from the Theory of Heat Transfer;472
5.9.4;7.9.4. A Qualitative Study of How Diffusion Affects the Response of an Interface to a Constant Current;473
5.9.5;7.9.5. A Quantitative Treatment of How Diffusion to an Electrode Affects the Response with Time of an Interface to a Constant Current;475
5.9.6;7.9.6. The Concept of Transition Time;478
5.9.7;7.9.7. Convection Can Maintain Steady Interfacial Concentrations;482
5.9.8;7.9.8. The Origin of Concentration Overpotential;487
5.9.9;7.9.9. The Diffusion Layer;489
5.9.10;7.9.10. The Limiting Current Density and Its Practical Importance;492
5.9.11;7.9.11. The Steady-State Current–Potential Relation under Conditions of Transport Control;503
5.9.12;7.9.12. The Diffusion-Activation Equation;504
5.9.13;7.9.13. The Concentration of Charge Carriers at the Electrode;504
5.9.14;7.9.14. Current as a Function of Overpotential: Interfacial and Diffusion Control;505
5.9.15;7.9.15. The Reciprocal Relation;507
5.9.16;7.9.16. Reversible and Irreversible Reactions;508
5.9.17;7.9.17. Transport-Controlled Deelectronation Reactions;509
5.9.18;7.9.18. What Is the Effect of Electrical Migration on the Limiting Diffusion Current Density?;510
5.9.19;7.9.19. Some Summarizing Remarks on the Transport Aspects of Electrodics;511
5.10;7.10. HOW TO DETERMINE THE STEPWISE MECHANISMS OF ELECTRODIC REACTIONS;514
5.10.1;7.10.1. Why Bother about Determining a Mechanism?;514
5.10.2;7.10.2. What Does It Mean: “To Determine the Mechanism of an Electrode Reaction”?;515
5.10.3;7.10.3. The Mechanism of Reduction of on Iron at Intermediate pH’s;520
5.10.4;7.10.4. Mechanism of the Oxidation of Methanol;526
5.10.5;7.10.5. The Importance of the Steady State in Electrode Kinetics;531
5.11;7.11. ELECTROCATALYSIS;532
5.11.1;7.11.1. Introduction;532
5.11.2;7.11.2. At What Potential Should the Relative Power of Electrocatalysts Be Compared?;534
5.11.3;7.11.3. How Electrocatalysis Works;537
5.11.4;7.11.4. Volcanoes;541
5.11.5;7.11.5. Is Platinum the Best Catalyst?;543
5.12;7.12. THE ELECTROGROWTH OF METALS ON ELECTRODES;550
5.12.1;7.12.1. The Two Aspects of Electrogrowth;550
5.12.2;7.12.2. The Reaction Pathway for Electrodeposition;551
5.12.3;7.12.3. Stepwise Dehydration of an Ion; the Surface Diffusion of Adions;553
5.12.4;7.12.4. The Half-Crystal Position;558
5.12.5;7.12.5. Deposition on an Ideal Surface: The Resulting Nucleation;559
5.12.6;7.12.6. Values of the Minimum Nucleus Size Necessary for Continued Growth;562
5.12.7;7.12.7. Rate of an Electrochemical Reaction Dependent on 2D Growth;563
5.12.8;7.12.8. Surface Diffusion to Growth Sites;564
5.12.9;7.12.9. Residence Time;567
5.12.10;7.12.10. The Random Thermal Displacement;569
5.12.11;7.12.11. Underpotential Deposition;570
5.12.12;7.12.12. Some Devices for Building Lattices from Adions: Screw Dislocations and Spiral Growths;573
5.12.13;7.12.13. Microsteps and Macrosteps;581
5.12.14;7.12.14. How Steps from a Pair of Screw Dislocations Interact;584
5.12.15;7.12.15. Crystal Facets Form;585
5.12.16;7.12.16. Pyramids;591
5.12.17;7.12.17. Deposition on Single-Crystal and Polycrystalline Substrates;591
5.12.18;7.12.18. How the Diffusion of Ions in Solution May Affect Electrogrowth;592
5.12.19;7.12.19. About the Variety of Shapes Formed in Electrodeposition;593
5.12.20;7.12.20. Dendrites;595
5.12.21;7.12.21. Organic Additives and Electrodeposits;596
5.12.22;7.12.22. Material Failures Due to H Co-deposition;597
5.12.23;7.12.23. Would Deposition from Nonaqueous Solutions Solve the Problems Associated with H Co-deposition?;598
5.12.24;7.12.24. Breakdown Potentials for Certain Organic Solvents;598
5.12.25;7.12.25. Molten Salt Systems Avoid Hydrogen Codeposition;601
5.12.26;7.12.26. Photostimulated Electrodeposition of Metals on Semiconductors;602
5.12.27;7.12.27. Surface Preparation: The Established Superiority of Electrochemical Techniques;602
5.12.28;7.12.28. Electrochemical Nanotechnology;602
5.13;7.13. CURRENT-POTENTIAL LAWS FOR ELECTROCHEMICAL SYSTEMS;605
5.13.1;7.13.1. The Potential Difference across an Electrochemical System;605
5.13.2;7.13.2. The Equilibrium Potential Difference across an Electrochemical Cell;607
5.13.3;7.13.3. The Problem with Tables of Standard Electrode Potentials;608
5.13.4;7.13.4. Are Equilibrium Cell Potential Differences Useful?;613
5.13.5;7.13.5. Electrochemical Cells: A Qualitative Discussion of the Variation of Cell Potential with Current;618
5.13.6;7.13.6. Electrochemical Cells in Action: Some Quantitative Relations between Cell Current and Cell Potential;621
5.14;7.14. THE ELECTROCHEMICAL ACTIVATION OF CHEMICAL REACTIONS;628
5.15;7.15. ELECTROCHEMICAL REACTIONS THAT OCCUR WITHOUT INPUT OF ELECTRICAL ENERGY;631
5.15.1;7.15.1. Introduction;631
5.15.2;7.15.2. Electroless Metal Deposition;631
5.15.3;7.15.3. Heterogeneous “Chemical” Reactions in Solutions;633
5.15.4;7.15.4. Electrogenerative Synthesis;634
5.15.5;7.15.5. Magnetic Induction;635
5.16;7.16. THE ELECTROCHEMICAL HEART;637
6;CHAPTER 8 TRANSIENTS ;658
6.1;8.1. INTRODUCTION;658
6.1.1;8.1.1. The Evolution of Short Time Measurements2;658
6.1.2;8.1.2. Another Reason for Making Transient Measurements;660
6.1.3;8.1.3. Is there a Downside for Transients?;664
6.1.4;8.1.4. General Comment on Factors in Achieving Successful Transient Measurements;664
6.2;8.2. GALVANOSTATIC TRANSIENTS;666
6.2.1;8.2.1. How They Work;666
6.2.2;8.2.2. Chronopotentiometry;668
6.3;8.3. OPEN-CIRCUIT DECAY METHOD;669
6.3.1;8.3.1. The Mathematics;669
6.4;8.4. POTENTIOSTATIC TRANSIENTS;671
6.4.1;8.4.1. The Method;671
6.5;8.5. OTHER MATTERS CONCERNING TRANSIENTS;673
6.5.1;8.5.1. Reversal Techniques;673
6.5.2;8.5.2. Summary of Transient Methods;674
6.5.3;8.5.3. “Totally Irreversible,” etc.: Some Aspects of Terminology;675
6.5.4;8.5.4. The Importance of Transient Techniques;677
6.6;8.6. CYCLIC VOLTAMMETRY;679
6.6.1;8.6.1. Introduction;679
6.6.2;8.6.2. Beginning of Cyclic Voltammetry;681
6.6.3;8.6.3. The Range of the Cyclic Voltammetric Technique;682
6.6.4;8.6.4. Cyclic Voltammetry: Its Limitations;683
6.6.5;8.6.5. The Acceptable Sweep Rate Range;684
6.6.6;8.6.6. The Shape of the Peaks in Potential–Sweep Curves;685
6.6.7;8.6.7. Quantitative Calculation of Kinetic Parameters from Potential Sweep Curves;688
6.6.8;8.6.8. Some Examples;689
6.6.9;8.6.9. The Role of Nonaqueous Solutions in Cyclic Voltammetry;691
6.6.10;8.6.10. Two Difficulties in Cyclic Voltammetric Measurements;691
6.6.11;8.6.11. How Should Cyclic Voltammetry be Regarded?;695
6.7;8.7. LINEAR SWEEP VOLTAMMETRY FOR REACTIONS THAT INCLUDE SIMPLE ADSORBED INTERMEDIATES;695
6.7.1;8.7.1. Potentiodynamic Relations that Account for the Role of Adsorbed Intermediates;695
7;CHAPTER 9 SOME QUANTUM-ORIENTED ELECTROCHEMISTRY;712
7.1;9.1. SETTING THE SCENE;712
7.1.1;9.1.1. A Preliminary Discussion: Absolute or Vacuum-Scale Potentials;714
7.2;9.2. CHEMICAL POTENTIALS AND ENERGY STATES OF “ELECTRONS IN SOLUTION”;715
7.2.1;9.2.1. The “Fermi Energy” of Electrons in Solution;715
7.2.2;9.2.2. The Electrochemical Potential of Electrons in Solution and Their Quantal Energy States;718
7.2.3;9.2.3. The Importance of Distribution Laws;719
7.2.4;9.2.4. Distribution of Energy States in Solution: Introduction;720
7.2.5;9.2.5. The Distribution Function for Electrons in Metals;726
7.2.6;9.2.6. The Density of States in Metals;728
7.3;9.3 POTENTIAL ENERGY SURFACES AND ELECTRODE KINETICS;730
7.3.1;9.3.1. Introduction;730
7.3.2;9.3.2. The Basic Potential Energy Diagram;732
7.3.3;9.3.3. Electrode Potential and the Potential Energy Curves;736
7.3.4;9.3.4. How Bonding of Surface Radicals to the Electrode Produces Electrocatalysis;741
7.3.5;9.3.5. Harmonic and Anharmonic Curves;744
7.3.6;9.3.6. How Many Dimensions?;745
7.4;9.4. TUNNELING;746
7.4.1;9.4.1. The Idea;746
7.4.2;9.4.2. Equations of Tunneling;747
7.4.3;9.4.3. The WKB Approximation;749
7.4.4;9.4.4. The Need for Receiver States;751
7.4.5;9.4.5. Other Approaches to Quantum Transitions and Some Problems;751
7.4.6;9.4.6. Tunneling Through Adsorbed Layers at Electrodes and in Biological Systems;752
7.5;9.5. SOME ALTERNATIVE CONCEPTS AND THEIR TERMINOLOGY;753
7.5.1;9.5.1. Introduction;753
7.5.2;9.5.2. Outer Shell and Inner Shell Reactions;753
7.5.3;9.5.3. Electron-Transfer and Ion-Transfer Reactions;754
7.5.4;9.5.4. Adiabatic and Nonadiabatic Electrode Reactions;754
7.6;9.6. A QUANTUM MECHANICAL DESCRIPTION OF ELECTRON TRANSFER;756
7.6.1;9.6.1. Electron Transfer;756
7.6.2;9.6.2. The Frank–Condon Principle in Electron Transfer;761
7.6.3;9.6.3. What Happens if the Movements of the Solvent–Ion Bonds Are Taken as a Simple Harmonic? An Aberrant Expression for Free Energy Activation in Electron Transfer;761
7.6.4;9.6.4. The Primacy of Tafel’s Law in Experimental Electrode Kinetics;764
7.7;9.7. FOUR MODELS OF ACTIVATION;768
7.7.1;9.7.1. Origin of the Energy of Activation;768
7.7.2;9.7.2. Weiss–Marcus: Electrostatic;769
7.7.3;9.7.3. George and Griffith’s Thermal Model;771
7.7.4;9.7.5. The Librator Fluctuation Model;773
7.7.5;9.7.6. The Vibron Model;774
7.8;9.8. BOND-BREAKING REACTONS;775
7.8.1;9.8.1. Introduction;775
7.9;9.9. A QUANTUM MECHANICAL FORMULATION OF THE ELECTROCHEMICAL CURRENT DENSITY;778
7.9.1;9.9.1. Equations;778
7.10;9.10. A RETROSPECT AND PROSPECT FOR QUANTUM ELECTROCHEMISTRY;779
7.10.1;9.10.1. Discussion;779
8;APPENDIX. THE SYMMETRY FACTOR; DO WE UNDERSTAND IT?;783
8.1;A.1. Introduction: Gurney–Butler;783
8.2;A.2. Activation less and Barrierless;785
8.3;A.3. The Dark Side of ß;785
9;INDEX;792

Leseproben

9.1. SETTING THE SCENE (p. 1455-1456)

When Galvani and, separately, Volta, made their first hesitant electrochemical experiments, in the eighteenth century, the electricity with which they dealt was not understood. Faraday’s laws of 1834 (relating the amount of metal deposited in electrolysis to the amount of electricity passed) hinted at a particulate nature for electricity, and by 1897 J. J. Thompson had measured electric charge to mass ratio (e/m) for the charged "cathode corpuscles" he found in gas discharge tubes. By 1912, Millikan had measured the charge, on such particles, so that their mass was also known. The realization that the passage of electricity consists of the flow of these "electrons" is less than 100 years old.

The electron is the quintessential particle in electrochemistry. But it has turned out that its properties bear within them a mystery, the nature of which is still debated. For Davidson and Germer (1927), and then G. P. Thompson (1928) found that the corpuscles that J. J. Thompson (1897) had measured possessed a Jekyl and Hyde character. Material corpuscles they could be (with definite mass and charge) but lo!—they could also behave as if they were waves.

Earlier on, in 1901, experimental results on the variation of the intensity of radiation from hot black bodies as a function of the wavelengths emitted by the radiation led Planck to suggest that energy itself went about as "quanta," bits of energy, the amount of energy in each bit being related to the frequency of the radiation concerned. Bohr’s 1913 interpretation of the H atom spectra then involved an assumption to which he needed to fit the facts: only certain frequencies of radiation were "allowed." The radiations emitted from hot atoms consisted of a number of spectral lines having frequencies of and etc. The positions in the atoms issuing radiation at these specific frequencies are called quantum states. Electrons could be in these states, but not in others.

By 1926, just in time for Davidson and Germer’s 1927 experiment, Schrödinger put into mathematical form an idea due to de Broglie (1924). It was that the sometimes wavelike character of electrons could be the basis of the quantum states. The waves had to "fit into" the space available (e.g., the distance between two nuclei in a solid), and it was this need to fit and make a "standing wave" that made only certain states—certain wavelengths (or energies)—possible. All this material is described in introductory textbooks of physics and chemistry. However, it is interesting to recall the headlines here because the very first application to a chemical theme of the ideas of waves in quantum mechanics was to explain how electrons were emitted from, or accepted by, electrodes. This was the achievement of Ronald Gurney,1 the first physical electrochemist, and much of this chapter is based on developments that sprang from his seminal paper of 1931. In this paper, he related electric currents across the electrode solution interface to the tunneling of electrons through energy barriers formed between the electrode and the ions or molecules in the first layer next to the electrode (possessing "electronic states").

Our chapter has two broad themes. In the first, we will consider some aspects of quantum states relevant to electrochemical systems. In the second, the theme will be the penetration of the barrier and the relation of the current density (the electrochemical reaction rate) to the electric potential across the interface. This concerns a quantum mechanical interpretation of Tafel’s experimental work of 1905, which led (1924- 1930) to the Butler–Volmer equation.