MODERN ASPECTS OF ELECTROCHEMISTRY

No. 28

LIST OF CONTRIBUTORS

A. J. ARVIA Instituto de Investigaciones Fisicoquimicas Te6ricas y Aplicadas Universidad Nacional de La Plata (I 900) La Plata, Argentina

MANFRED W. BREITER Institute of Technical Electrochemistry Technical University of Vienna A-I060 Vienna, Austria

S. G. CHRISTOV Bulgarian Academy of Sciences Institute of Physical Chemistry Sofia 1040, Bulgaria

C. GUTIERREZ Instituto de Quimica Fisica "Rocasolano," Consejo Superior de Investigaciones Cientificas Madrid-28006, Spain

DAVID A. HARRINGTON Department of Chemistry University of Victoria Victoria, British Columbia Canada, V8W 2Y2

WOLFGANG J. LORENZ Institute of Physical Chemistry University of Karlsruhe D-76l3l Karlsruhe, Germany

GEORG SAEMANN-ISCHENKO Institute of Physics University of Erlangen-Nuremberg D-91058 Erlangen, Germany

R.C. SAL V AREZZA Instituto de Investigaciones Fisicoquimicas Te6ricas y Aplicadas Universidad Nacional de La Plata (I 900) La Plata, Argentina

MANUEL P. SORIAGA Department of Chemistry Texas A&M University College Station, Texas 77843

JOHN L. STICKNEY Department of Chemistry University of Georgia Athens, Georgia 30602

ANDRZEJ WIECKOWSKI Department of Chemistry University of Illinois Urbana, Illinois 61801

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MODERN ASPECTS OF ELECTROCHEMISTRY

No. 28

Edited by

B.E. CONWAY University of Ottawa

Ottawa, Ontario, Canada

J. O'M. BOCKRIS Texas A&M University College Station, Texas

and

RALPH E. WHITE University of South Carolina Columbia, South Carolina

SPRINGER SCIENCE+BUSINESS MEDIA, LLC

The Library of Congress cataloged the first volume of this title as follows:

Modern aspects of electrochemistry, no. [1] Washington Butterworths, 1954— v. illus., 23 cm. No. 1—2 issued as Modern aspects series of chemistry. Editors: no 1- J. Bockris (with B. E. Conway, No. 3 - ) Imprint varies: no. 1, New York, Academic Press.—No. 2, London, Butterworths. 1. Electrochemistry—Collected works. I. Bockris, John O'M.ed. II. Conway, B.E. ed.

(Series: Modern aspects series of chemistry)

QD552.M6 54-12732 rev

ISBN 978-1-4899-1720-1 ISBN 978-1-4899-1718-8 (eBook) DOI 10.1007/978-1-4899-1718-8

© Springer Science+Business Media New York 1996 Originally published by Plenum Press, New York in 1996

Softcover reprint of the hardcover 1st edition 1996

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AU 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

Preface

The present volume comprises five chapters covering topics having relevance both in fundamental and in applied aspects of the field of electrochemical science. On the fundamental side, two of the contributions are concerned with the currently very active area of electrochemical surface science.

The first chapter, jointly authored by Soriaga, Harrington, Stickney, and Wieckowski, from four different university laborato­ries, addresses the general topic of application of ultrahigh-vacuum surface analytical methods to electrochemical studies of single­crystal surfaces, and the processes and species that can arise thereon. A comprehensive description is given of the instrumenta­tion involved in this field and its use for quantitative characteriza­tion of electrosorption processes, including in situ studies.

In the second chapter, Gutierrez gives a specialized account of the hitherto little used procedure of in situ potential-modulated reflectance spectroscopy at noble-metal electrode surfaces applied in the ultraviolet region to the examination of electronic transitions of CO chemisorbed in various states at such metals. Interestingly, because of the wavelength range involved, none of the problems of background bulk solvent water bands arise as they do in the IR potential-modulated surface spectroscopies. Some of the transi­tions that can be observed are independent of the metal substrate and are characteristic only of the geometry and coordination of the chemisorbed CO on the surface.

In Chapter 3, Lorenz, Saemann-Ischenko, and Breiter review the progress that has been made in quite recent years on the electro­chemical behavior and properties of superconductors of the ceramic

v

vi Preface

oxide type that exhibit a high critical transition temperature, Te. Since the spectacular discovery of these materials a few years ago, a natural development was their examination by various electro­chemical means, including the study of selected electrochemical processes at their surfaces, in order to establish if aspects of their electrochemical behavior also show some discontinuities at, or around, the Te. This chapter gives a succinct comparative account of what has been discovered in recent years in this field through electrochemical studies at low temperatures.

In Chapter 4, Christov gives a detailed analysis of treatments of electron transfer in homogeneous and heterogenous systems, the latter applying to electrode/solution interfaces. This is, of course, a topic of continuing central interest in theoretical aspects of elec­trode processes, and his contribution illustrates how complex this topic has now become, relative to the situation in earlier years.

The concluding chapter, by Salvarezza and Arvia, deals with new approaches to surface roughness, a fundamental and practical matter in electrocatalysis. These authors deal with the important question of how to characterize, for example, in terms of fractal models, and how to measure, for example, by means of voltammetry and impedance electrochemical techniques, surface roughness on various scales.

B. E. Conway University of Ottawa

J. O'M. Bockris Texas A&M University

R. E. White University of South Carolina

Contents

Chapter 1

ULTRAHIGH-VACUUM SURFACE ANALYTICAL METHODS IN ELECTROCHEMICAL STUDIES OF

SINGLE-CRYSTAL SURFACES

Manuel P. Soriaga, David A. Harrington, John L. Stickney, and Andrzej Wieckowski

I. Introduction.................................. 1 II. Experimental Procedures. . . . . . . . . . . . . . . . . . . . . . .. 3

1. Electrode-Surface Preparation. . . . . . . . . . . . . . . . .. 3 2. Interfacial Characterization Techniques. . . . . . . . .. 5 3. Instrumentation Designs ...................... 28

III. Fundamental Aspects. . . . . . . . . . . . . . . . . . . . . . . . . .. 34 1. The Emersion Process. . . . . . . . . . . . . . . . . . . . . . .. 34 2. Perturbations Caused by Evacuation and Surface

Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 36 IV. Case Studies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 40

1. Electrochemical Double Layer . . . . . . . . . . . . . . . .. 40 2. Underpotential Electrodeposition. . . . . . . . . . . . . .. 41 3. Molecular Adsorption . . . . . . . . . . . . . . . . . . . . . . .. 44

V. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 52 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 53

vii

viii Contents

Chapter 2

POTENTIAL-MODULATED REFLECTANCE SPECTROSCOPY STUDIES OF THE ELECTRONIC

TRANSITIONS OF CHEMISORBED CARBON MONOXIDE

c. Gutierrez

I. Introduction .................................. 61 1. Carbon Monoxide, the Model Molecule in

Chemisorption .............................. 61 2. Electronic Transitions of Chemisorbed CO ....... 62

II. Potential-Modulated Reflectance Spectroscopy (Electrolyte Electroreflectance) ................... 62 1. Introduction ................................ 62 2. Instrumental Setup ........................... 63 3. Applications of Potential-Modulated Reflectance

Spectroscopy ............................... 65 III. Chemisorption of CO on Various Metals ........... 66

1. Detection by PMRS of a Transition at 4 e V Due to Chemisorbed CO ............................ 66

2. Verification of the Identification of the PMRS Band at 270 nm as Due to Chemisorbed CO ........... 67

3. PMR Spectra of the Two Types of Linear CO Chemisorbed on Pt .......................... 74

4. PMR Spectra of CO Chemisorbed on Pt in Alkaline Solution ................................... 74

5. PMRS of CO Chemisorbed on Ru .............. 75 6. PMRS of CO Chemisorbed on Rh .............. 76 7. PMRS of CO Chemisorbed on Pd .............. 79 8. PMRS of CO Chemisorbed on Au .............. 81 9. Origin of the Linear Dependence of the Energy

of a PMRS Band on Electrode Potential ......... 86 IV. Chemisorption of Methanol and Ethanol on Various

Metals ....................................... 89 1. Introduction ................................ 89

Contents ix

2. Chemisorption of Methanol and Ethanol on Pt . . .. 89 3. Chemisorption of Methanol and Ethanol on Rh . .. 92 4. Chemisorption of Methanol and Ethanol on Pd. . .. 97

V. Assignment of the Observed PMRS Bands of Chemisorbed CO . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 99 1. Electronic Valence Levels of Chemisorbed CO . . .. 99 2. EELS and Differential Reflectance Spectroscopy

Studies on Chemisorbed CO . . . . . . . . . . . . . . . . . .. 99 3. Possible Assignment of the Electronic Transition

at4eV .................................... 102 VI. Conclusions .................................. 103

References ........................................ 103

Chapter 3

LOW-TEMPERATURE ELECTROCHEMISTRY AT HIGH-Tc SUPERCONDUCTOR/IONIC

CONDUCTOR INTERFACES

Wolfgang J. Lorenz, Georg Saemann-Ischenko, and Manfred W. Breiter

I. Introduction .................................. 107 II. Experimental Setup for Low-Temperature

Electrochemistry ............................... 114 III. Superionic Conductors at Low Temperature ......... 120 IV. Liquid and Frozen Electrolytes at Low Temperature .. 136 V. HTSC/Solid Electrolyte Junctions ................. 136

VI. HTSClFrozen Electrolyte and HTSC/Liquid Electrolyte Junctions ..................................... 151

VII. Theoretical Considerations ...................... 153 VIII. Future Aspects of Low-Temperature

Electrochemistry ............................... 158 Appendix A ....................................... 159 Appendix B ....................................... 160

x Contents

Notation .......................................... 162 References ........................................ 164

Chapter 4

QUANTUM THEORY OF CHARGE-TRANSFER PROCESSES IN CONDENSED MEDIA

S. G. Christov

I. Introduction .................................. 167 II. General Theory of Reaction Rates ................ 169

1. Adiabatic and Diabatic Electronic Surfaces ....... 169 2. Transition Probabilities ....................... 176 3. Rate Equations ............................. 179 4. Some General Consequences of the Rate

Equations .................................. 185 III. Application of the General Rate Theory to the

Harmonic Oscillator Model ...................... 188 1. Basic Rate Equations ......................... 188 2. The High-Temperature Range ................. 190 3. The Intermediate-Temperature Range ........... 194 4. The Low-Temperature Range .................. 196

IV. The Stochastic Reaction Rate Approach ............ 201 1. Classical Theory ............................. 201 2. Quantum Theory ............................ 206

V. Special Types of Charge-Transfer Processes ......... 209 1. Electron-Transfer Processes in Solution .......... 209 2. Proton-Transfer Processes in Solution ........... 222 3. Electrode Processes .......................... 257 4. Charge Transfer in Solid Systems ............... 280

VI. Conclusions .................................. 283 References ........................................ 285

Contents

Chapter 5

A MODERN APPROACH TO SURFACE ROUGHNESS APPLIED TO ELECTROCHEMICAL SYSTEMS

R. C. Salvarezza and A. J. Arvia

xi

I. Introductory Remarks .......................... 289 II. Solid Surfaces ................................. 292

1. General Considerations ....................... 292 2. Regular and Irregular Real Surfaces ............. 293

III. Fractal Description of Surface Disorder ............ 299 1. Topological, Euclidean, and Fractal

Dimensions ................................ 299 2. Marginal, Self-Affine, and Self-Similar Fractals .... 302 3. Surface, Mass, and Pore Fractality: Roughness

and Porosity ................................ 305 IV. Development of Irregular Surfaces ................ 307

1. Metal Vapor Deposition ...................... 309 2. Metal Electrodeposition ...................... 310

V. Modeling Roughness Development. .......... : .... 311 1. The Dynamic Scaling of Rough Surfaces ......... 311 2. Surface Growth Models ....................... 313 3. Dynamic Scaling and Growth Models for Self-

Affine Fractal Surfaces ....................... 319 VI. Experimental Methods for the Characterization of

Irregular Surfaces .............................. 319 1. Surface Area Measurement .................... 319 2. Characterization of Rough Surfaces ............. 323

VII. Results and Model Validity ...................... 343 1. Structural Aspects ........................... 343 2. Kinetic Aspects ............................. 349 3. Pattern Transitions: Monte Carlo Simulation ...... 353

VIII. Roughness Decay and Development ............... 356 1. Roughness Decay at Metal Electrodes ........... 356

xii Contents

2. Metal Atom Surface Mobility and Roughness Development ............................... 361

IX. Conclusions .................................. 362 Notation .......................................... 364 References ........................................ 367

Cumulative Author Index . ............................ 375

Cumulative Title Index . .............................. 391

Subject Index ...................................... 401