โ Scribed by Sergio Trasatti
No coin nor oath required. For personal study only.
The structure of interfacial water at metal electrodes is inferred and discussed on the basis of the experimental evidence resulting from the use of such diverse techniques and approaches as thermodesorption spectra, electroreflection spectroscopy, dielectric studies, quantum-chemical calculations, work function measurements, electrochemical adsorption and kinetic investigations, heat of adsorption, potential of zero charge determination. The behaviour at metal surfaces is shown to parallel that at oxides since in both cases the same factors are basically involved. Qualitative and quantitativedifferences are pointed out forsp,d-and sd-metals. Besides the more usuat aspect of water preferential orientation, also the role played by the surface electrons of the metal is illustrated. Structural effects related to the atomic configuration of the surface are finally taken into consideration.
The role of the interfacial region at the electrode/solution boundary can hardly be overemphasized. Any electrochemical event is affected by its structure[i, 21 and this is important not only from the fundamental but also from the practical point of view. The purpose of this paper is to illustrate some of the experimental facts, ascertained by diverse techniques, indicating that structuring of the solvent (in particular, water) occurs near a solid surface (in particular, metal surfaces). Since covering all relevant aspects is impossible here, the treatment will be restricted to uncharged solid surfaces in contact with solutions of not specifically adsorbed electrolytes.
Particles in the surface region of two immiscible phases in contact experience unbalanced forces. For this reason, the properties of the phase in the interfacial region differ from those in the bulk. In particular, polar [or polarizablc) molecules usually adopt a preferential orientation [3,4].
Many different techniques are used to investigate the structure and the properties of the interfacial region. These are distinguished into traditional and non-traditional ones [5]. The former are the classical electrochemical methods: measurements of potenlial of zero charge, capacitance, interfacial tension. These techniques enable pieces of direct information to be obtained from the interface. Radiometric measurements may be included in this category. Indirect information on the structure of the interfaclal region can be obtained from electrochemical adsorption and kinetic studies [2,4,6].
The latter group of techniques includes those largely borrowed from the field of surface physlcs [7, 81. They are distinguishable[5,9] into rn situ and rx ;ritu techniques.
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The electrochemical behavior of the interface between lithium (Li) alloy electrodes containing a small amount of metal [aluminum (Al) or tin (Sn)] and a propylene carbonate (PC)-based electrolyte has been investigated. The contents of Al and Sn were below 3.0 wt.%. AC impedance analysis revealed tha