Electrolyte interfaces

IHP) (the Helmholtz condenser formula is used in connection with it), located at the surface of the layer of Stem adsorbed ions, and an outer Helmholtz plane (OHP), located on the plane of centers of the next layer of ions marking the beginning of the diffuse layer. These planes, marked IHP and OHP in Fig. V-3 are merely planes of average electrical property the actual local potentials, if they could be measured, must vary wildly between locations where there is an adsorbed ion and places where only water resides on the surface. For liquid surfaces, discussed in Section V-7C, the interface will not be smooth due to thermal waves (Section IV-3). Sweeney and co-workers applied gradient theory (see Chapter III) to model the electric double layer and interfacial tension of a hydrocarbon-aqueous electrolyte interface [27]. 

The equations of electrocapillarity become complicated in the case of the solid metal-electrolyte interface. The problem is that the work spent in a differential stretching of the interface is not equal to that in forming an infinitesimal amount of new surface, if the surface is under elastic strain. Couchman and co-workers [142, 143] and Mobliner and Beck [144] have, among others, discussed the thermodynamics of the situation, including some of the problems of terminology. 

While the v-a plots for ionized monolayers often show no distinguishing features, it is entirely possible for such to be present and, in fact, for actual phase transitions to be observed. This was the case for films of poly(4-vinylpyri-dinium) bromide at the air-aqueous electrolyte interface [118]. In addition, electrostatic interactions play a large role in the stabilization of solid-supported lipid monolayers [119] as well as in the interactions between bilayers [120]. 

Kolb D M 1996 Reconstruction phenomena at metal-electrolyte interfaces Prog. Surf. Sc/. 51 109... 

The Nemst equation above for the dependence of the equilibrium potential of redox electrodes on the activity of solution species is also valid for uncharged species in the gas phase that take part in electron exchange reactions at the electrode-electrolyte interface. For the specific equilibrium process involved in the reduction of chlorine ... 

Fischer P R, Daschbach J L and Richmond G L 1994 Surface second harmonic studies of Si(111 )/electroltye and Si(111 )/Si02/electrolyte interfaces Chem. Phys. Lett. 218 200-5... 

Figure Bl.28.10. Schematic representation of an illuminated (a) n-type and (b) p-type semiconductor in the presence of a depletion layer fonned at the semiconductor-electrolyte interface.

The presented examples clearly demonstrate tliat a combination of several different teclmiques is urgently recommended for a complete characterization of tire chemical composition and tire atomic stmcture of electrode surfaces and a reliable interiDretation of tire related results. Stmcture sensitive metliods should be combined witli spectroscopic and electrochemical teclmiques. Besides in situ techniques such as SXS, XAS and STM or AFM, ex situ vacuum teclmiques have proven tlieir significance for tlie investigation of tlie electrode/electrolyte interface. 

Wang J, Ocko B M, Davenport A J and Isaacs H I 1992 In situ diffraction and reflectivity studies of the Au(111 )/electrolyte interface Reconstruction and anion adsorption Phys. Rev B 34 10 321-38... 

Kolb D M and Franke C 1982 Surface states at the metal-electrolyte interface Appl. Phys A 49 379-87... 

Gordon J G, Melroy O R and Toney M F 1995 Structure of metal-electrolyte interfaces copper on gold(111), water on silver(111) Electrochim. Acta 40 3-8... 

Zegenhagen J, Kazimirov A, Scherb G, Kolb D M, Smilgies D-M and Feidenhans l R 1996 X-ray diffraction study of a semiconductor/electrolyte interface n-GaAs(001)/H2S04( Cu) 1996 Surf. Sc/. 352-354 346-51... 

A signihcant problem in tire combination of solid electrolytes with oxide electrodes arises from the difference in thermal expansion coefficients of the materials, leading to rupture of tire electrode/electrolyte interface when the fuel cell is, inevitably, subject to temperature cycles. Insufficient experimental data are available for most of tire elecuolytes and the perovskites as a function of temperature and oxygen partial pressure, which determines the stoichiometty of the perovskites, to make a quantitative assessment at the present time, and mostly decisions must be made from direct experiment. However, Steele (loc. cit.) observes that tire electrode Lao.eSro.rCoo.aFeo.sOs-j functions well in combination widr a ceria-gadolinia electrolyte since botlr have closely similar thermal expansion coefficients. 

A. Valance. Porous silicon formation Stability analysis of the silicon-electrolyte interface. Phys Rev B 52 8323, 1995. 

Polarization can be divided into activation polarization and concentration polarization , Activation polarization is an electrochemical reaction that is controlled by the reaction occurring on the metal-electrolyte interface. Figure 4-418 illustrates the concept of activation polarization where hydrogen is being reduced over a zinc surface. Hydrogen ions are adsorbed on the metal surface they pick up electrons from the metal and are reduced to atoms. The atoms combine to... 

Current enters through the metal-electrolyte interface of the anode, which is usually made from the same metal as is plated on the cathode. The anode dissolves replacing the metal lost at the cathode ... 

In galvanic cells it is only possible to determine the potential difference as a voltage between two half-cells, but not the absolute potential of the single electrode. To measure the potential difference it has to be ensured that an electrochemical equilibrium exists at the phase boundaries, e.g., at the electrode/electrolyte interface. At the least it is required that there is no flux of current in the external and internal circuits. 

The early literature (until 1982) is summarized in Refs. [1] and [2], Hundreds of papers have been published since then (most of them in since 1994) and it is impossible to summarize all of them here. The Proceedings of the conferences mentioned above are good, sources of recent developments though sometimes incomplete. Since the early 1980s new systems have been introduced. The most important of these are lithium-ion batteries (which have lithiated carbonaceous anodes) and polymer-electrolyte batteries. Until 1991 very little was published on the Li/polymer-electrolyte interface [3, 4], The application of the SEI model to Li-PE batteries is ad-... 

It is now well established that in lithium batteries (including lithium-ion batteries) containing either liquid or polymer electrolytes, the anode is always covered by a passivating layer called the SEI. However, the chemical and electrochemical formation reactions and properties of this layer are as yet not well understood. In this section we discuss the electrode surface and SEI characterizations, film formation reactions (chemical and electrochemical), and other phenomena taking place at the lithium or lithium-alloy anode, and at the Li. C6 anode/electrolyte interface in both liquid and polymer-electrolyte batteries. We focus on the lithium anode but the theoretical considerations are common to all alkali-metal anodes. We address also the initial electrochemical formation steps of the SEI, the role of the solvated-electron rate constant in the selection of SEI-building materials (precursors), and the correlation between SEI properties and battery quality and performance. 

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