COllJprehensive Treatise of ElectrochellJistry. Volume 7 Kinetics and Mechanisms of Electrode Processes

Transcription

1 COllJprehensive Treatise of ElectrochellJistry Volume 7 Kinetics and Mechanisms of Electrode Processes

2 COMPREHENSIVE TREATISE OF ELECTROCHEMISTRY Volume 1 Volume 2 Volume 3 Volume 4 Volume 5 Volume 6 Volume 7 THE DOUBLE LAYER Edited by J. O'M. Bockris, Brian E. Conway, and Ernest Yeager ELECTROCHEMICAL PROCESSING Edited by J. O'M. Bockris, Brian E. Conway, Ernest Yeager, and Ralph E. White ELECTROCHEMICAL ENERGY CONVERSION AND STORAGE Edited by J. O'M. Bockris, Brian E. Conway, Ernest Yeager, and Ralph E. White ELECTROCHEMICAL MATERIALS SCIENCE Edited by J. O'M. Bockris, Brian E. Conway, Ernest Yeager, and Ralph E. White THERMODYNAMIC AND TRANSPORT PROPERTIES OF AQUEOUS AND MOLTEN ELECTROLYTES Edited by Brian E. Conway, J. O'M. Bockris, and Ernest Yeager ELECTRODICS: TRANSPORT Edited by Ernest Yeager, J. O'M. Bockris, Brian E. Conway, and S. Sarangapani KINETICS AND MECHANISMS OF ELECTRODE PROCESSES Edited by Brian E. Conway, J. O'M. Bockris, Ernest Yeager, S. U. M. Khan, and Ralph E. White

3 Comprehensive Treatise of Electrochemistry Volume 7 Kinetics and Mechanisms of Electrode jdrocesses Edited by Brian E. Conway University of Ottawa Ottawa, Ontario, Canada J. O'M. Bockris Texas. A&M University College Station, Texas Ernest Yeager Case Western Reserve University Cleveland, Ohio S.U.M. Khan Texas A&M University College Station, Texas Ralph E. White Texas A&M University College Station, Texas PLENUM PRESS NEW YORK AND LONDON

4 Main entry under title: Library of Congress Cataloging in Publication Data Kinetics and mechanisms of electrode processes. (Comprehensive treatise of electrochemistry; v. 7) Includes bibliographical references and index. 1. Electrodes. 2. Electrochemistry. 3. Chemical reaction, Rate of. l. Conway, B. E. II. Series. QD552.C64 vol /7s [541.3 /724] [QD571] ISBN-13: DOl: / e-isbn-13: Plenum Press, New York Softcover reprint of the hardcover 1 st edition 1983 A Division of Plenum Publishing Corporation 233 Spring Street, New York, N.Y All rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher

5 Contributors A. J. Appleby Electric Power Research Institute, 3412 Hillview Avenue, Palo Alto, California John O'M. Bockris Department of Chemistry, Texas A&M University, College Station, Texas Evengi B. Budevski Central Laboratory of Electrochemical Power Sources, Bulgarian Academy of Sciences, Sofia 1040, Bulgaria B. E. Conway Department of Chemistry, University of Ottawa, Ottawa, Ontario, Canada Aleksandar R. Despic Faculty of Technology and Metallurgy, University of Belgrade, Belgrade, Yugoslavia R. R. Dogonadze Institute of Electrochemistry of the Academy of Sciences of the USSR, Moscow, USSR M. Enyo The Research Institute for Catalysis, Hokkaido University, Sapporo, Japan D. Inman Department of Metallurgy & Materials Science, Imperial College, London SW7 2BP, United Kingdom Shahed U. M. Khan Department of Chemistry, Texas A&M University, College Station, Texas L. I. Krishtalik Institute of Electrochemistry of the Academy of Sciences of the USSR, Moscow, USSR A. M. Kuznetsov Institute of Electrochemistry of the Academy of Sciences of the USSR, Moscow, USSR v

6 vi CONTRIBUTORS D. G. Lovering Chemistry Branch, RM.C.S., Shrivenham, Swindon SN6 8LA, United Kingdom R. Memming Philips GmbH Forschungslaboratorium Hamburg, D-2000 Hamburg 54, Federal Republic of Germany E. J. Judd Eltech Systems Corporation, Technical Center, Fairport, Ohio Andrzej Sadkowski Institute of Physical Chemistry, Warsaw, Poland M. R. Tarasevich Institute of Electrochemistry of the Academy of Sciences of the USSR, Moscow, USSR Ernest Yeager Case Laboratories for Electrochemical Studies, Case Western Reserve University, Cleveland, Ohio

7 Preface to Comprehensive Treatise of Electrochemistry Electrochemistry is one of the oldest defined areas in physical science, and there was a time, less than 50 years ago, when one saw "Institute of Electrochemistry and Physical Chemistry" in the chemistry buildings of European universities. But after early brilliant developments in electrode processes at the beginning of the twentieth century and in solution chemistry during the 1930s, electrochemistry fell into a period of decline which lasted for several decades. Electrochemical systems were too complex for the theoretical concepts of the quantum theory. They were too little understood at a phenomenological level to allow the Ubiquity in application in so many fields to be comprehended. However, a new growth began faintly in the late 1940s, and clearly in the 1950s. This growth was exemplified by the formation in 1949 of what is now called The International Society for Electrochemistry. The usefulness of electrochemistry as a basis for understanding conservation was the focal point in the founding of this Society. Another very important event was the choice by NASA in 1958 of fuel cells to provide the auxiliary power for space vehicles. With the new era of diminishing usefulness of the fossil fuels upon us, the role of electrochemical technology is widened (energy storage, conversion, enhanced attention to conservation, direct use of electricity from nuclear-solar plants, finding materials which interface well with hydrogen). This strong new interest is not only in the technological applications of electrochemistry. Quantum chemists have taken an interest in redox processes. Organic chemists are interested in situations where the energy of electrons is as easily controlled as it is at electrodes. Some biological processes are now seen in electrodic terms, with electron transfer to and from materials which would earlier have been considered to be insulators. vii

8 viii PREFACE TO COMPREHENSIVE TREATISE It is now time for a comprehensive treatise to look at the whole field of electrochemistry. The present treatise was conceived in 1974, and the earliest invitations to authors for contributions were made in The completion of the early volumes has been delayed by various factors. There has been no attempt to make each article emphasize the most recent situation at the expense of an overall statement of the modern view. This treatise is not a collection of articles from Recent Advances in Electrochemistry or Modern Aspects of Electrochemistry. It is an attempt at making a mature statement about the present position in the vast area of what is best looked at as a new interdisciplinary field. Texas A & M University University of Ottawa Case Western Reserve University Texas A & M University John O'M. Bockris Brian E. Conway Ernest B. Yeager Ralph E. White

9 Preface to Volume 7 The present volume deals with electrode kinetics, the heart of electrochemistry. After much progress in the 19th century, at the beginning of the present century the field went into a period of decline from which it did not emerge for about fifty years. Now, it is by far the most populated area in electrochemical research. It must be admitted, however, that the selection of authors for the present Volume has not been an easy one because there are controversies at the basis of the subject. There is no agreement upon the nature of the activation processes in the fundamental act. A number of fundamental electrochemists limit their activities to the study of redox systems (because of the complexities of bonding in other systems), whereas others consider that by so doing many of the essential features of electrode kinetics remain uninvestigated and that, therefore, a less representative picture of the field may be obtained. Partly because of the heterogeneous character of the interests of fundamental electrochemists, it seemed desirable to have similar fields described by authors with alternative viewpoints. University of Ottawa Texas A&M University Case Western Reserve University Texas A&M University Texas A&M University B. E. Conway J. O'M. Bockris E. Yeager s. U. M. Khan R. White ix

10 Contents 1. Quantum Electrochemical Kinetics: Continuum Theory R. R. Dogonadze and A. M. Kuznetsov 1. Introduction 1 2. The Model 8 3. General Expressions for the Transition Probability Transition Probability for Fixed Coordinates of the Ions and Reactants Proton Transfer Reactions Proton Transfer in the Case of Strong Coupling with the Medium Proton Transfer in the Case of Weak Coupling with the Medium Effect of the Discrete Structure of the Electrical Double Layer on the Kinetics The Step of Electrochemical Desorption of Hydrogen Atoms The Role Played by the Electronic Structure of the Electrode Experimental Verification of the Theory 36 References Molecular Aspects of Quantum Electrode Kinetics S. U. M. Khan and J. O. M. Bockris 1. Introduction Correlation between Electrochemical Electron and Spectroscopic Photon Transfer Process Applicability of Time-Depe!1dent Perturbation Theory for Electron Transfer Processes at Electrodes Proton Transfer at Interfaces Gurney's Quantum Mechanical Model of Proton Transfer Butler's Modification of Gurney's Model The Quantum Character of Proton Transfer Degree of Validity of the WKB Tunneling Probability Expression for Proton Transfer A Model of Electrochemical Hydrogen Evolution Reaction Quantal Aspects of Photoelectrochemical Kinetics Photoeffect at Metal-Solution Interface Non-Tafel Behavior of Photocurrent at Metal-Solution Interface Photoeffect at Semiconductor-Solution Interface 64./

11 xii CONTENTS 6. Tunneling at the Oxide-Covered Electrode Fermi Energy in Solution Distribution of Electron States in Ions in Solution The Adiabaticity and Nonadiabaticity in Electron Transfer Reactions Landau-Zener Formulation Transmission Coefficient, K, for Homogeneous Redox Reactions Transition Probability of the Electron at the Electrode-Solution Interface Concluding Remarks 83 References Kinetics of Electrochemical Reactions at Metal-Solution Interfaces L. I. Krishtalik 1. Introduction: Steps of Electrode Processes Phenomenological Theory of the Elementary Act of an Electrode Reaction BrlSnsted-Polanyi Relation and Electrode Reaction Activation Energy Electronic Work Function and Related Values in Electrochemical Kinetics Activity Coefficient of an Activated Complex Temperature Dependence of Electrode Reaction Rates Activationless and Barrierless Electrode Processes Formal Kinetics of Electrode Reactions Kinetic Equations Stoichiometric Numbers Electrode Double-Layer Structure and Electrode Reaction Rate Basic Relations Hydrogen Evolution Reduction of Anions Electrode Reactions of Organic Compounds 165 References Electrocatalysis A. J. Appleby 1. Introduction 2. Electrocatalysis and Catalysis 2.1. General 2.2. Effect of Potential on Rate 3. The Rates of Complex Processes

12 CONTENTS 4. Potential Energy Diagrams and Electrocatalysis 4.1. General 4.2. Some Correlations 5. Some Quantum Mechanical Aspects 5.1. General 5.2. Radiationless Transfer Theories 6. Some Electrocatalytic Reactions 6.1. General 6.2. Hydrogen Electrode Reaction 6.3. Oxygen Electrode Reactions 6.4. Organic Oxidations 6.5. Chlorine Evolution 6.6. General Remarks on Practical Electrocatalysts References xiii Hydrogen Electrode Reaction on Electrocatalytically Active Metals M. Envo 1. Introduction Adsorption of Hydrogen on Metal Electrodes Hydrogen Wave by a Potential Sweep Technique Adsorption Isotherm for Atomic Hydrogen Structure of the Hydrogen Wave and Experiments on Single-Crystal Planes Basic Kinetic Equations Experimental Behavior and Possible Mechanisms-Existence of a Unique Rate-Determining Step Possible Reaction Routes and Mechanisms The Stoichiometric Number The Tafel Slope Magnitude of the Tafel Slope The Reaction Orders Mechanism with No Unique Rate-Determining Step Tracer Experiments Tafel Lines and Reaction Orders Absence of rds and Affinity Distribution among the Constituent Steps Synthesis of the Overall Kinetics Transient Experiments on the Pd Hydrogen Electrode Related Topics Effect of Catalytic Poisons upon the Individual Step Rates Hydrogen Pressure Equivalent to Hydrogen Overpotential Electrolytic Hydrogenation of Organic Substances Electrode Materials Pure Metals Composite Materials 292 References 293

13 xiv CONTENTS 6. Oxygen Electrochemistry M. R. Tarasevich, A. Sadkowski, and E. Yeager 1. Introduction Thermodynamics of the Oxygen Electrode Open-Circuit Potentials Oxygen Adsorbed Species and Anodic Films on Platinum and Other Noble Metals Electrochemical Studies In Situ Optical Studies In Situ Surface Conductivity Measurements Ex Situ Characterizations The Anodic Oxygen Evolution Reaction (OER) General Features Kinetics and Mechanisms of the Oxygen Evolution Reaction on Metal and, Oxide Electrodes Cathodic Reactions of Oxygen (Oxygen Cathodes) The General Scheme of Parallel and Series Reactions of Oxygen and Hydrogen Peroxide The Kinetics of Molecular Oxygen Reduction on Different Metallic Electrodes Oxygen Reduction on Nonmetallic Materials Concluding Remarks 388 References Deposition and Dissolution of Metals and Alloys. Part A: Electrocrystallization E. B. Budevski 1. Introduction Kinetics of Atom Incorporation The Structure of a Crystalline Surface The Propagation Rate of Steps The Current Density on a Stepped Crystal Face Metal Deposition on a Perfect Crystal Face Energy and Rate of Formation of Two-Dimensional Nuclei Kinetics of Step Propagation and Mechanism of Metal Deposition Deposition Kinetics on Perfect Crystal Faces Metal Deposition on Faces Intersected by Screw Dislocations The Theory of Spiral Growth Current Density and Morphology of Growth Electrolytic Phase Formation Equilibrium Forms and Forms of Growth of Crystals The Nucleation Rate The Nucleation-Rate-Overpotential Relation Comparison with Experimental Data 443

14 CONTENTS 6. Conclusions and Outlook References xv Deposition and Dissolution of Metals and Alloys. Part B: Mechanisms, Kinetics, Texture, and Morphology A. R. Despic 1. Introduction Specific Features of the Thermodynamics of Metal and Alloy Phase Formation and Degradation Equilibration of a Metal Surface with Electrolyte Containing Metal Ions-the Problem of the Reversible Potential Reversible Potentials of Alloys Underpotential Deposition of Metals on Foreign Substrates Effect of Interactions of the Metal Ion in Solution on the Reversible Potential Effect of ph on Electrode Potential Likely Mechanisms of Metal Ion Discharge and Their Kinetic Consequences Mechanism and Kinetics of the Electrode Process Pseudocapacitance Effects and the Concentration of Intermediate Species Effect of Anions on the Kinetics of Metal Deposition and Dissolution Effect of Substrate on the Kinetics of Activation-Controlled Reactions of Metals Kinetics of Codeposition of Metals and Effects on Alloy Phase Formation Totally Irreversible Dissolution of Metals The "Floating" Electrode Potential Dissolution with the Formation of Insoluble Substances Acceleration of Anodic Dissolution of Metals under Strain Formation and Physical Properties of Metallic Deposits Obtained under Conditions of Slow Discharge and Incorporation Effect of Substrate on the Growth of the Deposit Factors Affecting Grain Size in a Compact Deposit The Appearance of Texture in Metal Deposits Development of Stress in Metal Deposits Effect of Slow Transport of Species to the Electrode on Surface Morphology of Metal Deposits Amplification of Surface Roughness The Appearance and Growth of Dendrites The Formation of Metal Powders Effect of Periodically Changing Conditions of Deposition The Phenomenon of Electropolishing Effect of Adsorption of Foreign Substances on Surface Morphology of Metal Deposits The Growth of Whiskers Leveling in Metal Deposition 523

15 xv; 8. Conclusion References CONTENTS Processes at Semiconductor Electrodes R.Memming 1. Introduction Potential and Charge Distribution at Solid-Electrolyte Interfaces Energy Levels in Solids and Electrolytes Absolute and Conventional Electrode Potentials Energy Levels in Solids Energy Levels in Electrolytes Energy Levels at Semiconductor-Electrolyte Interfaces Electrode Kinetics Rate of Electron Transfer (Theory) Electrode Reactions in Electrolytes without Redox Systems Redox Processes Electron Transfer Processes at Organic Insulator Electrodes Evaluations of Exchange Currents and Determination of Reorientation Energies Photoefiects Photopotentials and Photocurrents Applications in Electrode Kinetics Photostimulated Reactions at Organic Electrodes Reactions of Excited Molecules at Electrodes Energy Levels of Excited Molecules Electron Transfer Process Relaxation Phenomena, Quenching, Supersensitization Competitive Photochemical Reactions in the Electrolyte Production of Excited Molecules by Electron Transfer Conclusions 588 References Electrochemistry in Molten Salts D. Inman and D. G. Lovering 1. Introduction 1.1. General 1.2. Complex Ions 1.3. Acidity and Basicity 1.4. emf Series and Reference Electrodes 2. Electroanalytical Aspects 2.1. General Methodology 2.2. Ion Transport 2.3. Ionic Adsorption

16 CONTENTS 2.4. Coupled Chemical Reactions 2.5. Solution Stability 3. The Metal-Molten Salt Interface 3.1. General Aspects 3.2. The Electrical Multilayer Close to Eq = The Electrical Multilayer Remote from Eq = 0 4. Kinetics and Mechanisms of Electrode Reactions 4.1. Problems and Methods of Approach 4.2. Electrode Reactions Involving Homogeneous Redox Reactions 4.3. Electrode Reactions at Liquid Metal Electrodes 4.4. Electrode Reactions at Solid Metal Electrodes 4.5. The Electroactivity of Nonmetallic Anions 5. Applications 5.1. General 5.2. Metals Recovery and Processing 5.3. Batteries 5.4. Fuel Cells 5.5. Corrosion 5.6. Anodizing 6. Experimental Procedures 6.1. Materials, Electrodes, and Operating Conditions 6.2. Nitrates 6.3. Halides 6.4. Other Salts References xvii Organic Electrode Processes: Kinetics, Mechanisms, and Prospects for Commercial Development E. J. Rudd and 8. E. Conway 1. Historical Aspects Introduction and Nature of Organic Electrode Processes Classification of Organic Electrode Reactions Kinetic Equations for Electrochemical Reactions Factors in the Kinetics of Organic Electrode Reactions Electrode Potential, E, and the Rate Equations for Electron Transfer Reactions Treatments for More Complex Electrochemical Reactions Dependence of Rates of Organic Electrode Reactions on the Electrode Material Reaction Yields in Relation to Coulombic Efficiency and Conditions of Electrolysis Current Efficiencies and Coulombic Yields Significance of Controlled Potential Electrolysis Coulometry Preparative Methods 669

17 xv;;; CONTENTS 6. Role of Adsorption in Electro-Organic Reactions Factors in Adsorption and the Formulation of Isotherms Methods for Investigation of Adsorption of Organic Substances Reaction Order and Adsorption in Kinetics of Electro-Organic Processes Adsorption and Solvation: Solvent Effects in Organic Adsorption Adsorption and the Electrode Metal Organic Reactions under Diffusion Control at Electrodes Introduction Diffusion-Limited Electrode Processes at Solid Metals Polarographic Conditions: Diffusion at Mercury Drops The Mass Transport Problems in Preparative Electro-Organic Chemistry and Cell Design Polarographic Methods and Related Techniques for the Study of Electro- Organic Reactions Introduction Fundamental Aspects of Polarography Criteria of Polarographic Reversibility What Information May Be Obtained from Classical Polarography? Other Electrochemical Techniques Related to Polarography Polarographic Studies of ph Effects and Reaction Mechanisms Steric Aspects of Electro-Organic Reaction Mechanisms Adsorption of Intermediates and Stereochemical Effects Alkyl Halide Reduction and Stereochemical Effects Isotope Effects in Mechanistic Studies Electrocatalytic Types of Reaction with Small Organic Molecules Anodic Reactions with Thick-Film Oxides on Electrodes Reactions at Bulk-Type Base Metal Oxide Films Reactions of Organic Substances at High Anodic Potentials on Thick Noble Metal Oxide Films Discussion of Some Reactions and Their Mechanisms That Have Possibilities for Commercial Development Oxidation of Aliphatic Hydrocarbons Anodic Substitution Reactions with Aromatic Hydrocarbons Electroreduction Processes Coupling Reactions Electroinitiated Polymerizations Economic and Commercial Aspects of Organic Electrode Processes Conclusions Regarding Industrial Applications 761 References 762 Index 773