Introduction to the fundamental concepts of electrochemistry

This book was initially prepared as lecture notes for an electrochemistry course which has been presented regularly in Southampton and elsewhere during the past fifteen years. The course seeks to develop an understanding of electrochemical experiments and to illustrate the applications of electrochemical methods to, for example, the study of redox couples, homogeneous chemical reactions, and surface science. In many studies, several of the techniques will be equally applicable, but there are situations where one technique has a unique advantage and hence the course also seeks to discuss the selection of method and the design of experiments to aid the solution of both chemical and technological problems. 

Hence the structure of this book quite deliberately follows that of the course. The theoretical background to electrochemistry and the discussion of electrochemical techniques are developed as parallel themes. The general principles of instrumentation and experiment design are introduced in later chapters, while those readers interested in the mathematical and computational techniques used in electrochemistry are directed to the appendix. The purpose of this first chapter is to give an overview of electrochemistry and to summarise those important equations and ideas which will be used repeatedly throughout the book and which will also be more fully justified in later chapters. 

An electrode reaction is a heterogeneous chemical process involving the transfer of electrons to or from a surface, generally a metal or a semiconductor. The electrode reaction may be an anodic process whereby a species is oxidised by the loss of electrons to the electrode, e.g. 

By convention [1], the current density, 7, for an anodic process is a positive quantity. Conversely, the charge transfer may be a cathodic reaction in which a species is reduced by the gain of electrons from the electrode, e.g. 

Electrolysis is only possible in a cell with both an anode and a cathode, and, because of the need to maintain an overall charge balance, the amount of reduction at the cathode and oxidation at the anode must be equal. The total chemical change is found by adding the two individual electrode reactions for example, the chemical change in a chlor-alkali membrane or diaphragm cell is obtained by adding Equations (1.3) and (1.8), i.e. 

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Other more recent, important events could also be mentioned here, although it is really during these two centuries that the fundamental basis of electrochemistry was shaped. It is interesting to note that most concepts relating to the existence of ions and the reactions involving the exchange of charge were put forward before the atomic theory of matter was fully accepted. It was in 1803 that Dalton reintroduced the concept of the atom, which had been previously buried for centuries. Thomson s work on the electron was carried out in 1887, and the introduction of the Bohr model dates back to 1913. 

This chapter mainly deals with the fundamentals of H2/air PEM fuel cells, including fuel cell reaction thermodynamics and kinetics, as well as a brief introduction to the single fuel cell and the fuel cell stack. The electrochemistry and reaction mechanisms of H2/air fuel cell reactions, including the anode HOR and the cathode ORR, are discussed in depth. Several concepts related to PEM fuel cell performance, such as fuel cell polarization curves, OCV, hydrogen crossover, and fuel cell efficiencies, are also introduced. With respect to fuel cell stmctures and components, the material properties and effects on fuel cell performance are also discussed. In addition, several important conditions for fuel cell operation, including temperature, pressure, RH, and gas stoichiometries and flow rates, and their effects on fuel cell operation, are also briefly presented. This chapter provides the requisite baseline knowledge for the remaining chapters. 

The object of this book is to provide an introduction to electrochemistry in its present state of development. An attempt has been made to explain the fundamentals of the subject as it stands today, devoting little or no space to the consideration of theories and arguments that have been discarded or greatly modified. In this way it is hoped that the reader will acquire the modern point of view in electrochemistry without being burdened by much that is obsolete. In the opinion of the writer, there have been four developments in the past two decades that have had an important influence on electrochemistry. They are the activity concept, the interionic attraction theory, the proton-transfer theory of acids and bases, and the consideration of electrode reactions as rate processes. These ideas have been incorporated into the structure of the book, with consequent simplification and clarification in the treatment of many aspects of electrochemistry. 

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