Modern Aspects Of Electrochemistry No 7

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.

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.

The present volume contains five chapters covering areas of contemporary interest in the fields of electrolyte solutions, the state of solvent molecules at electrode surfaces, charged colloid interfaces, surface chemistry of oxide electrodes and electro chemistry, and bioelectrochemistry of charge transfer complexes. The first chapter, by Barthel, Wachter, and Gores, covers the topic of conductance of nonaqueous pro tic and aprotic electro lyte solutions. This field is not only of intrinsic interest in itself, illustrating the important departures of ion-transport behavior in organic solvents from that, more well known, in water, but the information and extensive new data presented in this chapter will be of interest to those working with nonaqueous alkali-metal batteries where the conductivity and ion-association behavior of electrolytes in various solvents other than water is of great importance. The second chapter is devoted to a very fundamental and ubiquitous aspect of electrochemistry of electrodes: the state of solvent molecules, adsorbed and oriented, at their surfaces. The role of solvent adsorption and orientation in double-layer proper ties, it will be recalled, remained poorly understood until the early 1960s. This chapter, by Trasatti, gives a thorough account of the present state of knowledge of solvent orientation at electrode interfaces and of the unsuspected (until recent years) role it plays in properties of the double layer and in determining the potential profile at charged metal surfaces in solution.

Recognized experts present incisive analysis of both fundamental and applied problems in this continuation of a highly acclaimed series. Topics discussed include: A thorough and mathematical treatment of periodic phenomena, with consideration of new theories about the transition between order' and chaos'; Impedance spectroscopy as applied to the study of kinetics and mechanisms of electrode processes; The use of stoichiometric numbers in mechanism analysis; The electro-osmotic dewatering of clays with important implications for the processing of industrial waste and geotechnical; stabilization; Magnetic effects in electrolytic processes and the electrolytic Hall effect; and The computer analysis and modeling of mass transfer and fluid flow. These authoritative studies will be invaluable for researchers in engineering, electrochemistry, analytical chemistry, materials science, physical chemistry, and corrosion science.

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.

The fourth volume of Modern Aspects of Electrochemistry is being prepared at a time of great growth of interest in electro chemistry. The situation can be summarized by saying that the realization is spreading among scientists that electrochemistry represents a broad interdisciplinary field, which has applications to many areas in physics, chemistry, metallurgy, and biology. Among the reasons for this awakening is the reorientation of what is understood under electrochemistry toward electrodics "the study of charged interfaces"-with the ionic-solution aspects of electrochemistry being regarded increasingly as aspects of physical chemistry which are helpful auxiliaries to the broad subject of charged interfaces. The pervasiveness of electrochemistry be comes clearer when one recalls that most interfaces carry a charge, or undergo local charge transfers, even though they are not con nected with a source of power. A further reason for the rapid increase in electrochemical studies arises from the technological aspects, in particular in energy conversion and storage, syntheses, extractions, devices, the stability and finishing of surfaces, the treatment of water, etc. The fact that electrodics allows the conversion of chemical to electric energy and the storage of the latter, at the same time producing fresh water as a by-product, presents an aspect of the subject which appears to have far-reaching significance.