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This volume comprises six chapters on aspects of fundamental and
applied electrochemical science that will be of interest both to
researchers in the basic areas of the subject and to those involved
in aspects of electrochemical technologies. Chapter 1 is the first
part of a 2-part, major contribution by Joachim Maier on Solid
State Electrochemistry: Thermodynamics and Kinetics of Charge
Carriers in Solids. Part 2 will follow in volume 39 to be published
in year 2005. This contribution reviews modern concepts of the
equilibria involving charge carriers in solids in terms of
concentrations of defects in solids and at grain-boundaries,
including doping effects. Complementarily, kinetics of charge
transfer and ion transfer are treated in some detail in relation to
conductance, kinetics of surface processes and electrode-kinetics
involving solid-state processes. This chapter will be of major
interest to electrochemists and physicists in the semiconductor
field and that involving ionic solids. In the second chapter,
Appleby presents a detailed discussion and review in modern terms
of a central aspect of electrochemistry: Electron Transfer
Reactions With and Without Ion Transfer. Electron transfer is the
most fundamental aspect of most processes at electrode interfaces
and is also involved intimately with the homogeneous chemistry of
redox reactions in solutions.
The first model for the distribution of ions near the surface of a
metal electrode was devised by Helmholtz in 1874. He envisaged two
parallel sheets of charges of opposite sign located one on the
metal surface and the other on the solution side, a few nanometers
away, exactly as in the case of a parallel plate capacitor. The
rigidity of such a model was allowed for by Gouy and Chapman inde
pendently, by considering that ions in solution are subject to
thermal motion so that their distribution from the metal surface
turns out diffuse. Stern recognized that ions in solution do not
behave as point charges as in the Gouy-Chapman treatment, and let
the center of the ion charges reside at some distance from the
metal surface while the distribution was still governed by the
Gouy-Chapman view. Finally, in 1947, D. C. Grahame transferred the
knowledge of the struc ture of electrolyte solutions into the model
of a metal/solution interface, by en visaging different planes of
closest approach to the electrode surface depending on whether an
ion is solvated or interacts directly with the solid wall. Thus,
the Gouy-Chapman-Stern-Grahame model of the so-called electrical
double layer was born, a model that is still qualitatively
accepted, although theoreti cians have introduced a number of new
parameters of which people were not aware 50 years ago.
The present collection of articles follows the arrangement used in
previous volumes. Solutions are discussed first, surfaces and
double layers second, electrode kinetics third, and then the
applied subjects. The introduction of spectroscopic methods to
electrochemistry is well exemplified by NMR studies of ionic
solutions, as represented here in the detailed article by E. von
Goldammer. Correspondingly, the spectroscopic approach can be
applied to surfaces, and B. G. Baker has written an introduction to
this topic for electrochemists from the point of view of gas phase
measurements. One of the topics which begins to reach a degree of
sophistica tion in electrode process chemistry is the adsorption of
organic species on electrodes, and this topic is described in our
volume by the well-known electrochemist M. W. Breiter. The work has
much rele vance to the corresponding electrode kinetics and
oxidation of organic materials. Much less sophisticated is the
position in the electrochemistry of sulfide minerals, but it has
seemed worthwhile to have the present record described by D. F. A.
Koch; his chapter demonstrates the value of qualitative
electrochemical studies in this field. The Hydrogen Economy is
perhaps an example of straw fire in electrochemistry, for its great
popularity beginning in 1973 reflects an interest which can hardly
grow larger. However, much discussion of the Hydrogen Economy is
concerned with its nonelectrochemical v vi Preface aspects and D.
P. Gregory gives here the latest from the hydrogen front, with
emphasis on the electrochemistry."
In the last decade, the evolution of electrochemistry away from
concern with the physical chemistry of solutions to its more
fruitful goal in the study of the widespread consequences of the
transfer of electric charges across interphases has come to
fruition. The turning of technology away from an onward rush,
regardless, to progress which takes into account repercussions of
techno logical activity on the environment, and the consequent need
for a reduction and then termination of the injection of CO into 2
the atmosphere (greenhouse effect), together with a reckoning with
air and water pollution in general, ensures a long-term need for
advances in a basic knowledge of electrochemical systems, an
increased technological use of which seems to arise from the
environmental necessities. But a mighty change in attitude needs to
spread among electro chemists (indeed, among all surface chemists)
concerning the terms and level in which their field is discussed.
The treatment of charge transfer reactions has often been made too
vaguely, in terms, it seemed, of atom transfer, with the
electron-transfer step, the essence of electrochemistry, an implied
accompaniment to the transfer of ions across electrical double
layers. The treatment has been in terms of classical mechanics,
only tenable while inadequate questions were asked concerning the
behavior of the electron in the interfacial transfer. No process
demands a more exclusively quantal discussion than does electron
transfer.
This volume continues the development of the Modern Aspects series
in the electrochemical field. The series is now 18 years old, and
it is relevant to note the degree of evolution that electro
chemistry has undergone during this time, for it affects the
character of the articles chosen. The trend is towards development
of inter disciplinary areas of electrochemical science, with full
stress upon the many directions of applications of knowledge of
electrode processes. The degree of import which should be attached
to electro chemical science arises from the changes in technology
which must be made during the next few decades. These clearly
involve a massive electrification and the gradual elimination of
the present fossil fuel economy, for both ecological and economic
reasons. Research on the fundamental aspects of the field-slow in
development to a standard-must be promulgated, but its
justification is the modern provisionofa basis for the needed
future electrochemical technology. One vast area of potential
application of electrochemical concepts is omitted by the present
attitude. It is, of course, the electro biological aspect, perhaps,
finally, the largest area of all for fruitful applications. These
concepts are reflected in the editors' choice of chapters. Quantum
mechanical descriptions of surfaces must be bravely faced.
Oscillatory aspects of electrochemical systems are often met in
nature and demand attention at a fundamental level. Organic
electrochemistry is in an ascending phase. With the electro
biological v Preface vi article, we hope to stimulate a beginning
of electrodic applications in this area.
The first chapter in the present volume takes up a well-known theme
in modern context: the ideas concerning non-Stokesian mechanisms of
ion transport. We are happy that one of the great pioneers of
modern electrochemistry, T. Erdey-Gniz, in collaboration with S.
Lengyel, has consented to write this article for us. Along with it
is a solution-oriented article in spectroscopic vein, namely, that
by A. Covington and K. E. Newman on the analysis of solution
constituents by means of nuclear magnetic resonance studies.
Progress in the electrochemistry of the double layer has perked up,
and the advances have been triggered from critical experiments, one
showing that fluoride ions are specifically adsorbed, and the other
showing that the position of maximum disorder of the water
molecules occurs at a charge opposite to that needed for interpreta
tions of capacitance humps in terms of water molecules. M. A.
Habib, who has contributed to the theory in this area, reviews the
con sequences of these changes in information. The rise in the
price of energy toward a situation in which sources other than the
fossil fuels become economical implies much for the fuel cell and
electrocatalysis. It has long been known that electrocatalysis in
real situations was more than a consideration of exchange current
densities, and a gap remains in the formulation of the theory of
supports for such catalysts, although Boudart has stressed so much
the vital nature of them. P. Stonehart and K. A. Kinoshita describe
progress in this area.
As the subject of electrochemistry moves into the final quarter of
the century, a number of developed areas can be assessed in depth
while some new areas provide quantitatively and qualitatively novel
data and results. The first chapter, by Kebarle, deals with an
example of the latter type of field in which new information of the
energetics and equilibria of reactions between ions and solvent
molecules is studied in the gas phase and provides interesting
basic information for treatments of ions in solution, i.e., ionic
solvation. Chapter 2, by Hamann, discusses the behavior of
electrolyte solutions under high pressures, a matter of intrinsic
interest in relation to ion-solvent interaction and the structural
aspects of the properties of ionic solutions, especially in water.
This topic is also of current interest with regard to the physical
chemistry of the marine environment, especially at great depths. In
the article by Bloom and Snook (Chapter 3), models for treatments
of molten salt systems are examined quantitatively in relation to
the structure of molten ionic liquids and to the statistical
mechanical approaches that can be meaningfully made to interpret
their properties and electrochemical behavior.
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.
This volume comprises six chapters on aspects of fundamental and
applied electrochemical science that will be of interest both to
researchers in the basic areas of the subject and to those involved
in aspects of electrochemical technologies. Chapter 1 is the first
part of a 2-part, major contribution by Joachim Maier on Solid
State Electrochemistry: Thermodynamics and Kinetics of Charge
Carriers in Solids. Part 2 will follow in volume 39 to be published
in year 2005. This contribution reviews modern concepts of the
equilibria involving charge carriers in solids in terms of
concentrations of defects in solids and at grain-boundaries,
including doping effects. Complementarily, kinetics of charge
transfer and ion transfer are treated in some detail in relation to
conductance, kinetics of surface processes and electrode-kinetics
involving solid-state processes. This chapter will be of major
interest to electrochemists and physicists in the semiconductor
field and that involving ionic solids. In the second chapter,
Appleby presents a detailed discussion and review in modern terms
of a central aspect of electrochemistry: Electron Transfer
Reactions With and Without Ion Transfer. Electron transfer is the
most fundamental aspect of most processes at electrode interfaces
and is also involved intimately with the homogeneous chemistry of
redox reactions in solutions.
The first model for the distribution of ions near the surface of a
metal electrode was devised by Helmholtz in 1874. He envisaged two
parallel sheets of charges of opposite sign located one on the
metal surface and the other on the solution side, a few nanometers
away, exactly as in the case of a parallel plate capacitor. The
rigidity of such a model was allowed for by Gouy and Chapman inde
pendently, by considering that ions in solution are subject to
thermal motion so that their distribution from the metal surface
turns out diffuse. Stern recognized that ions in solution do not
behave as point charges as in the Gouy-Chapman treatment, and let
the center of the ion charges reside at some distance from the
metal surface while the distribution was still governed by the
Gouy-Chapman view. Finally, in 1947, D. C. Grahame transferred the
knowledge of the struc ture of electrolyte solutions into the model
of a metal/solution interface, by en visaging different planes of
closest approach to the electrode surface depending on whether an
ion is solvated or interacts directly with the solid wall. Thus,
the Gouy-Chapman-Stern-Grahame model of the so-called electrical
double layer was born, a model that is still qualitatively
accepted, although theoreti cians have introduced a number of new
parameters of which people were not aware 50 years ago."
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