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J. Appl. Cryst. (1994). 27, 131-132

Structure of electrified interfaces

Edited by J. Lipkowski and P. N. Ross

Pp. x + 406. Weinheim: VCH Verlagsgesellschaft GmbH, 1993
Price DM 196, £80.00. ISBN 3-527-28787-6

This book aims to describe, to a broad audience, the current understanding of the metal-solution interface of electrochemistry. The clear objective in this field of interfacial electrochemistry is to replace or augment the thermodynamic continuum models of the classic electrochemical double layer with microscopic models that explicitly incorporate the roles and structures of individual atoms and molecules. The evolution of perspective from macroscopic to microscopic is clearly work in progress and the book provides an excellent overview of current theory and recent experimental advances.

The use of single-crystal electrodes, a host of new surface probes and the ability to analyze a working electrochemical interface in situ and then ex situ using ultra-high-vacuum (UHV) techniques have led to rapid experimental advances. The first three chapters of the book provide an introduction to structural characterization and behavior of single-crystal metal-electrode surfaces. The tools of surface crystallography as applied in UHV are expertly reviewed by Michel Van Hove. Phillip Ross and Dieter Kolb go on to describe in situ methods of characterizing working `wet' electrodes by such techniques as surface extended X-ray absorption fine structure (SEXAFS), grazing-incidence X-ray scattering (GIXS), scanning tunneling microscopy (STM), atomic-force microscopy (AFM) and surface second-harmonic generation (SHG). Coupled wet electrochemistry and ex situ UHV-analysis studies are described, in which low-energy electron diffraction (LEED) and other electron spectroscopies are employed for structural analysis in UHV. These tools, coupled with cyclic voltammetry, are used to understand and discuss the structure of underpotentially deposited metal overlayers and potential-induced reconstruction of electrode surfaces.

The precise structure of directly adsorbed ions and diffusely ordered solvated ions that make up the electrochemical double layer at the electrochemical interface is difficult to characterize using any of the techniques above. In order to begin to understand the issues involved, Manuel Soriaga reviews molecular adsorption at single-crystal electrodes. Vibrational spectroscopy, via high-resolution electron energy-loss spectroscopy (HREELS) and infrared absorption spectroscopy (IRAS), is used to provide structural information on adsorbate bonding geometries through surface selection rules and analogies to inorganic cluster compounds. (It should be noted that recent dynamical LEED and SEXAFS studies have repudiated several nitric oxide site assignments based on vibrational spectroscopy, and this has diminished the enthusiasm for extrapolating the structures of cluster compounds to surfaces.) A metal electrode tempered by co-adsorbed ions and water defines an inner electrochemical layer, and Gerhard Pirug and Hans Bonzel discuss the simulation of such layers in UHV by co-adsorption of alkali metals and water. Wolfgang Schmickler and Karl Heinzinger provide analytical and molecular-dynamics-based theoreti-cal chapters on the electrochemical interface. The final experimental chapters of the book, by Zofia Borkowska and Ulrich Stimming and by Fred Wagner, examine the relationship between UHV simulations of electrochemical layers at cryogenic temperatures and `wet' electrochemistry. Water typically de-sorbs from metal electrodes at temperatures below 200 K. Nevertheless, the consensus of the authors is that diffusion and conductivity in favorable acid/water systems can be sufficient for purposes of electrochemical simulations at temperatures as low as 150 K. The chapter by Wagner is truly delightful as he thoughtfully catalogs the difficulties of connecting cryogenic UHV surface science with wet electrochemistry from experimental and theoretical points of view. Impressive results from UHV simulations of the electrochemical interface include the ability to count water molecules of ion hydration by thermal desorption and the spectroscopic identification of the hydronium ion (H3O+) by HREELS when HF or HCl is co-adsorbed with H2O on Pt(111).

The text provides a fine introduction to the field of interfacial electrochemistry. Its emphasis on current research and the many references to the primary literature suggest it will be much appreciated by the electrochemical community. Crystallographers will be particu-larly interested in the important role that diffraction techniques (LEED, GIXS and SEXAFS) have played in structural determinations of the inner electrochemical layer. At the same time, they may pause to reflect on how difficult it is to characterize the structure of the outer Helmholtz, or diffuse Gouy-Chapman, layer of solvated ions. Despite the difficulties of microscopically characterizing the electrochemical double layer, the text clearly indicates that rapid progress is being made in the emerging field of interfacial electrochemistry. Excellent accounts of the recent advances in and future prospects of the field are provided.

Ian Harrison

Department of Chemistry
University of Virginia
Charlottesville
VA 22901
USA


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