Modern Electrochemistry: Volume 1. An Introduction to an Interdisciplinary Area

682 Pages·1970·14.432 MB·English

by  John O’M. Bockris, Amulya K. N. Reddy (auth.)

VOLUME 1
MODERN
ELECTROCHEM'STRY
VOLUME 1
MODERN
ELECTROCHEMISTRY
An Introduction to an Interdisciplinary Area
John O'M. Bockris
Professor of Electrochemistry
University of Pennsylvania, Philadelphia, Pennsylvania
and
Amulya K. N. Reddy
Assistant Professor of Chemistry
Indian Institute of Science, Bangalore, India
<±'Springer Science+Business Media, LLC
First Printing-January 1970
Second Printing-March 1971
Library of Congress Catalog Card Number 68-19518
ISBN 978-1-4615-7469-9 ISBN 978-1-4615-7467-5 (eBook)
DOI 10.1007/978-1-4615-7467-5
© Springer Science+Business Media New York 1970
Originally published by Plenum Press, New York 1970
Softcover reprint of the hardcover 1st edition 1970
A Division of Plenum Publishing Corporation
227 West 17th Street, New York, N.Y. 10011
All rights reserved
No part of this publication may be reproduced in any form
without written permission from the publisher
PREFACE
This book had its nucleus in some lectures given by one ofus (J.O'M.B.)
in a course on electrochemistry to students of energy conversion at the
Vniversity of Pennsylvania. It was there that he met a number of people
trained in chemistry, physics, biology, metallurgy, and materials science,
all ofwhom wanted to know something about electrochemistry. The concept
of writing a book about electrochemistry wh ich 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 importanee. 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 effeets of an increasing concentration
in the atmosphere of carbon dioxide may be met. Corrosion is recognized
as having an electroehemical basis. The synthesis of nylon now contains
an important electroehemical stage. Some central biological mechanisms
have been shown to take place by means of electrochemical reactions. A
number of Ameriean organizations have recently recommended greatly
increased activity in training and research in electrochemistry at universities
in the Vnited States. Three new international journals of fundamental
electrochemical research were established between 1955 and 1965.
In contrast to this, physical ehe mists in V.S. universities seem-perhaps
partly because of the absence of a modern textbook in English-out of touch
with the revolution in fundamental interfacial electrochemistry which has
v
vi PREFACE
occurred since 1950. The fragments of electrochemistry wh ich are taught
in many D.S. universities belong not to the space age of electrochemically
powered vehicles, but to the age of thermodynamics and the horseless
carriage; they often consist of Nernst's theory of galvanic cells (1891)
together with the theory of Debye and Hückel (1923).
Electrochemistry at present needs several kinds of books. For example,
it needs a textbook in which the whole field is discussed at a strong theo
reticallevel. The most pressing need, however, is for a book which outlines
the field at a level which can be understood by people entering it from
different disciplines who have no previous background in the field but
who wish to use modern electrochemical concepts and ideas as a basis for
their own work. It is this need which the authors have tried to meet.
The book's aims determine its priorities. In order, these are:
1. Lucidity. The authors have found students who und erstand advanced
courses in quantum mechanics but find difficulty in comprehending a field
at whose center lies the quantum mechanics of electron transitions across
interfaces. The difficulty is associated, perhaps, with the interdisciplinary
character of the material: a background knowledge of physical chemistry
is not enough. Material has therefore sometimes been presented in several
ways and occasionally the same explanations are repeated in different
parts of the book. The language has been made informal and highly ex
planatory. It retains, sometimes, the lecture style. In this respect, the authors
have been influenced by The Feynmann Lectures on Physics.
2. Honesty. The authors have suffered much themselves from books
in which proofs and presentations are not complete. An attempt has been
made to include most of the necessary material. Appendices have been
often used for the presentation of mathematical derivations which would
obtrude too much in the text.
3. Modernity. There developed during the 1950's a great change in
emphasis in electrochemistry away from a subject which dealt largely with
solutions to one in which the treatment at a molecular level of charge
transfer across interfaces dominates. This is the "new electrochemistry,"
the essentials of which, at an elementary level, the authors have tried to
present.
4. Sharp variation is standard. The objective of the authors has been
to begin each chapter at a very simple level and to increase the level to
one which allows a connecting up to the standard of the specialized mono
graph. The standard at which subjects are presented has been intentionally
PREFACE vii
variable, depending particularly on the degree to which knowledge of the
material appears to be widespread.
5. One theory per phenomenon. The authors intend a teaching book,
which acts as an introduction to graduate studies. They have tried to
present, with due admission of the existing imperfections, a simple version
of that model which seemed to them at the time of writing to reproduce
the facts most consistently. They have for the most part refrained from
presenting the detailed pros and cons of competing models in areas in
which the theory is stilI quite mobile.
In respect to references and further reading: no detailed references to
the literature have been presented, in view of the elementary character of
the book's contents, and the corresponding fact that it is an introductory
book, largely for beginners. In the "further reading" lists, the policy is to
cite papers which are classics in the development of the subject, together
with papers of particular interest concerning recent developments, and in
particular, reviews of the last few years.
It is hoped that this book will not only be useful to those who wish
to work with modern electrochemical ideas in chemistry, physics, biology,
materials science, etc., but also to those who wish to begin research on
electron transfer at interfaces and associated topics.
The book was written mainly at the Electrochemistry Laboratory in
the University of Pennsylvania, and partly at the Indian Institute of Science
in Bangalore. Students in the Electrochemistry Laboratory at the University
of Pennsylvania were kind enough to give guidance frequentlyon how they
reacted to the clarity of sections written in various experimental styles and
approaches. For the last four years, the evolving versions of sections of
the book have been used as a partial basis for undergraduate, and so me
graduate, lectures in electrochemistry in the Chemistry Department of
the University.
The authors' acknowledgment and thanks must go first to Mr. Ernst
Cohn of the National Aeronautics and Space Administration. Without his
frequent stimulation, including very frank expressions of criticism, the book
might weIl never have emerged from the Electrochemistry Laboratory.
Thereafter, thanks must go to Professor B. E. Conway, University of
Ottawa, who gave several weeks of this time to making a detailed review
of the material. Plentiful help in editing chapters and effecting revisions
designed by the authors was given by the following: Chapters IV and V,
Dr. H. Wroblowa (Pennsylvania); Chapter VI, Dr. C. Solomons (Penn
sylvania) and Dr. T. Emi (Hokkaido); Chapter VII, Dr. E. Gileadi (Tel-
viii PREFACE
Aviv); Chapters VIII and IX, Prof. A. Despic (Belgrade), Dr. H. Wroblowa,
and Mr. J. Diggle (Pennsylvania); Chapter X, Mr. J. Diggle; Chapter XI,
Dr. D. Cipris (Pennsylvania). Dr. H. Wroblowa has to be particularly
thanked for essential contributions to the composition of the Appendix on
the measurement of Volta potential differences.
Constructive reactions to the text were given by Messers. G. Razumney,
B. Rubin, and G. Stoner of the Electrochemistry Laboratory. Advice was
often sought and accepted from Dr. B. Chandrasekaran (Pennsylvania),
Dr. S. Srinivasan (New York), and Mr. R. Rangarajan (Bangalore).
Comments on late drafts of chapters were made by a number of the
authors' colleagues, particularly Dr. W. McCoy (Office of Saline Water),
Chapter II; Prof. R. M. Fuoss (Yale), Chapter III; Prof. R. Stokes (Armi
dale), Chapter IV; Dr. R. Parsons (Bristol), Chapter VII; Prof. A. N.
Frumkin (Moscow), Chapter VIII; Dr. H. Wroblowa, Chapter X; Prof.
R. Staehle (Ohio State), Chapter XI. One ofthe authors (A.K.N.R.) wishes
to acknowledge his gratitude to the authorities of the Council of Scientific
and Industrial Research, India, and the Indian Institute of Science, Ban
galore, India, for various facilities, not the least of which were extended
leaves ofabsence. He wishes also to thank his wife and children for sacrificing
many precious hours which rightfully belonged to them.
CONTENTS
VOLUME 1
CHAPTER 1
Electrochemistry
1.1 Introduction ............................................. . 1
1.2 Electrons at and across Interfaces ....................... . 3
1.2.1 Many Properties of Materials Depend upon Events Occurring at Their
Surfaces ..................................................... . 3
1.2.2 Almost All Interfaces Are Electrified ............................ . 3
1.2.3 The Continuous Flow of Electrons across an Interface: Electrochemical
Reactions .................................................... . 7
1.2.4 Electrochemical and Chemical Reactions ........................ . 8
1.3 Basic Electrochemistry ................................... . 12
1.3.1 Electrochemistry before 1950 ................................... . 12
1.3.2 The Treatment of Interfacial Electron Transfer as a Rate Process:
The 1950's ................................................... . 17
1.3.3 Quantum Electrochemistry: The 1960's .......................... . 19
1.3.4 Ions in Solution, as weil as Electron Transfer across Interfaces ..... . 22
1.4 The Relation of Electrochemistry to Other Sciences ..... . 26
1.4.1 Some Diagrammatic Presentations .............................. . 26
1.4.2 Some Examples of the Involvement of Electrochemistry in Other Sciences 28
1.4.3 Electrochemistry as an Interdisciplinary Field, Apart from Chemistry? 29
1.5 Electrodics and Electronics .............................. . 31
1.6 Transients 32
ix
x CONTENTS
1.7 Electrodes are Catalysts ................................. . 34
1.8 The Electromagnetic Theory of Light and the Examination of
Electrode Surfaces ....................................... . 35
1.9 Science, Technology, Electrochemistry, and Time ........ . 38
1.9.1 Do Interfacial Charge-Transfer Reactions Have a Wider Significance
Than Has Hitherto Been Realized? ............................. . 38
1.9.2 The Relation between Three Major Advances in Science, and the Place
of Electrochemistry in the Developing World .................... . 39
CHAPTER 2
Ion-Solvent Interactions
2.1 Introduction ............................................. . 45
2.2 The Nonstructural Treatment of Ion-Solvent Interactions .. 48
2.2.1 A Quantitative Measure of Ion-Solvent Interactions .............. . 48
2.2.2 The Born Model: A Charged Sphere in a Continuum ............. . 49
2.2.3 The Electrostatic Potential at the Surface of a Charged Sphere ..... . 52
2.2.4 On the Electrostatics of Charging (or Discharging) Spheres ........ . 54
2.2.5 The Born Expression for the Free Energy of Ion-Solvent Interactions 56
2.2.6 The Enthalpy and Entropy of Ion-Solvent Interactions ........... . 59
2.2.7 Can One Experimentally Study the Interactions of a Single Ionic Species
with the Solvent? ............................................. . 61
2.2.8 The Experimental Evaluation of the Heat of Interaction of a Salt and
Solvent ...................................................... . 64
2.2.9 How Good Is the Born Theory? ................................ . 68
Further Reading ...................................................... . 72
2.3 Structural Treatment of the Ion-Solvent Interactions ..... . 72
2.3.1 The Structure of the Most Common Solvent, Water ............... . 72
2.3.2 The Structure of Water near an Ion ............................. . 76
2.3.3 The Ion-Dipole Model of Ion-Solvent Interactions ............... . 80
2.3.4 Evaluation of the Terms in the Ion-Dipole Approach to the Heat of
Solvation .................................................... . 88
2.3.5 How Good Is the Ion-Dipole Theory of Solvation? ............... . 93
2.3.6 The Relative Heats of Solvation of Ions on the Hydrogen Scale .... . 95
2.3.7 Do Oppositely Charged Ions of Equal Radii Have Equal Heats of
Solvation? ................................................... . 96
2.3.8 The Water Molecule Can Be Viewed as an Electrical Quadrupole .. . 98
2.3.9 The Ion-Quadrupole Model of Ion-Solvent Interactions ........... . 99
2.3.10 Ion-Induced-Dipole Interactions in the Primary Solvation Sheath .. 102
2.3.11 How Good Is the Ion-Quadrupole Theory of Solvation? .......... . 103
2.3.12 The Special Case of Interactions of the Transition-Metal Ions with Water 108
2.3.13 Some Summarizing Remarks on the Energetics of Ion-Solvent Inter-
actions ....................................................... 113
Further Reading .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
2.4 The Solvation Number .................................. . 117
2.4.1 How Many Water Molecules Are Involved in the Solvation of an Ion? 117