Electrochemical phase diagram

Surface-oxide formation begins after an adsorbate layer of oxygen or an 0-containing species on the electrode smface forms at more positive potentials ( 1.1 V). After time a bnlk-oxide continues growing. While different electrochemical techniques show evidence for oxide formation, the exact stracture and thickness of this oxide is still unclear. The conunon view is that oxide-growth first begins with the formation of a thin 

In order to compare stabilities of different oxygen overlayers and evaluate the electrochemical surface phase diagram of Pt(l 11) in contact with an aqueous electrolyte, we performed periodic DFT calculations on the energetics and stractures of oxygen adsorption at different coverages. Since the electrode is present in the solid phase, we assume the temperature and activity dependence of G to be small, and the contributions from configurational and 

The agreement between om phase diagram and the CV-measurements is surprisingly good, but one must consider the ramifications of our simple interface model and that polyciystalhne Pt had been used experimentally. The agreement might be due to the absence of specific ion adsorption on the 

Only oxygen adsorption has been studied here, and this phase diagram is only valid for electrode potentials where no H is adsorbed or hydride is formed on the surface. After having specified the electrode potential region at which the Pt(lll) surface is not oxidized, we use this surfaee model to study the water formation reaction. 

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Having established the theoretical reference electrode, we are now able to estimate electrochemical phase diagrams. The starting point of the electrochemical phase diagram is the relative stabihty of the different species on the surface. If we consider a metal electrode in an acid electrolyte, we obtain... 

Figure 2.14 Electrochemical phase diagram for chalcopyrite with elemental sulphur as metastable phase. Equilibrium lines (solid lines) correspond to dissolved species at 10 mol/L. Plotted points show the upper and lower limit potential of collectorless flotation of chalcopyrite reported from Sun (1990), Feng (1989) and Trahar (1984)...

Abstract In the beginning, the mixed potential model, which is generally used to explain the adsorption of collectors on the sulphide minerals, is illustrated. And the collector flotation of several kinds of minerals such as copper sulphide minerals, lead sulphide minerals, zinc sulphide minerals and iron sulphide minerals is discussed in the aspect of pulp potential and the nature of hydrophobic entity is concluded from the dependence of flotation on pulp potential. In the following section, the electrochemical phase diagrams for butyl xanthate/water system and chalcocite/oxygen/xanthate system are all demonstrated from which some useful information about the hydrophobic species are obtained. And some instrumental methods including UV analysis, FTIR analysis and XPS analysis can also be used to investigated sulphide mineral-thio-collector sytem. And some examples about that are listed in the last part of this chapter. 

Keywords collector flotation electrochemical phase diagram UV FTIR XPS... 

Electrochemical phase diagrams have been used to investigate the collector water mineral system in which the experimental potential for flotation is compared with thermodynamic equilibriums for reactions in mineral/oxygen/collector system to... 

Figure 4.30 Electrochemical phase diagram for the butyl xanthate/oxygen system and the observed lower and upper ( ) limiting flotation potential of galena and chalcopyrite at which flotation recovery is greater than 50% (EX 2 xlO mol/L)...

The three goals of the thermodynamic section are (1) to relate the thermodynamics of corrosion-related electrochemistry to concepts with which the reader may be familiar, (2) to describe the need for and characteristics of reference electrodes, and (3) to describe the origin, use, and limitations of electrochemical phase diagrams (a.k.a., F-pH or Pourbaix diagrams). 

Here, the first term on the right side denotes the standard chemical potential at temperature T and a water activity = 1- This expression allows us to evaluate the interfacial free energies from DFT calculations since all relevant quantities can be deduced from first principles. From these, we can obtain the electrochemical phase diagram. 

Figure 1.17 Electrochemical phase diagram showing the composition of co-deposited films. Parameter a is the flux ratio of Se(IV) and CU(II) ionic species to the surface. MSE...

Figure 6.14. Ab initio-calculated electrochemical phase diagram for the activation of water over Pd(l 11) to form either the surface hydride phase along with aqueous OH ions or a surface hydroxide phase along with hydronium ionP l.

The potential dependence of the velocity of an electrochemical phase boundary reaction is represented by a current-potential curve I(U). It is convenient to relate such curves to the geometric electrode surface area S, i.e., to present them as current-density-potential curves J(U). The determination of such curves is represented schematically in Fig. 2-3. A current is conducted to the counterelectrode Ej in the electrolyte by means of an external circuit (voltage source Uq, ammeter, resistances R and R") and via the electrode E, to be measured, back to the external circuit. In the diagram, the current indicated (0) is positive. The potential of E, is measured with a high-resistance voltmeter as the voltage difference of electrodes El and E2. To accomplish this, the reference electrode, E2, must be equipped with a Haber-Luggin capillary whose probe end must be brought as close as possible to... 

The general thermodynamic treatment of binary systems which involve the incorporation of an electroactive species into a solid alloy electrode under the assumption of complete equilibrium was presented by Weppner and Huggins [19-21], Under these conditions the Gibbs Phase Rule specifies that the electrochemical potential varies with composition in the single-phase regions of a binary phase diagram, and is composition-independent in two-phase regions if the temperature and total pressure are kept constant. 

In practice, for a ternary system, the decomposition voltage of the solid electrolyte may be readily measured with the help of a galvanic cell which makes use of the solid electrolyte under investigation and the adjacent equilibrium phase in the phase diagram as an electrode. A convenient technique is the formation of these phases electrochemically by decomposition of the electrolyte. The sample is polarized between a reversible electrode and an inert electrode such as Pt or Mo in the case of a lithium ion conductor, in the same direction as in polarization experiments. The... 

Chapters 7 to 9 apply the thermodynamic relationships to mixtures, to phase equilibria, and to chemical equilibrium. In Chapter 7, both nonelectrolyte and electrolyte solutions are described, including the properties of ideal mixtures. The Debye-Hiickel theory is developed and applied to the electrolyte solutions. Thermal properties and osmotic pressure are also described. In Chapter 8, the principles of phase equilibria of pure substances and of mixtures are presented. The phase rule, Clapeyron equation, and phase diagrams are used extensively in the description of representative systems. Chapter 9 uses thermodynamics to describe chemical equilibrium. The equilibrium constant and its relationship to pressure, temperature, and activity is developed, as are the basic equations that apply to electrochemical cells. Examples are given that demonstrate the use of thermodynamics in predicting equilibrium conditions and cell voltages. 

As with the phase diagrams and Pourbaix diagrams, the theoretical standard hydrogen electrode also allows us to calculate the relative energies of intermediates in electrochemical reactions. As an example, we investigate the oxygen reduction reaction (ORR). We look at the four proton and electron transfer elementary steps ... 

Rossmeisl J, Norskov JK, Taylor CD, Janik MJ, Neurock M. 2006. Calculated phase diagrams for the electrochemical oxidation and reduction of water over Pt(l 11). J Phys Chem B 110 21833-21839. 

Wang JH and Liu M. Computational study of sulfur-nickel interactions A new S-Ni phase diagram. Electrochem Commun 2007 9 2212-2217. 

Figure 4. Liquid—solid phase diagrams of EC/DMC, EC/ EMC, and PC/EC. (Reproduced with permission from ref 159 (Figure 9). Copyright 2000 The Electrochemical Society.)...

The importance of solvents and their effects play roles in electrochemistry as well. The properties of a family of novel quaternary ammonium salts based on the bis(triflu-oromethylsulfonyl)imide and triflate anions are reported in a paper by Sun (Sun et al., 1998). Binary phase diagrams for some of their mixtures and their electrochemical windows of stability were reported. The highest conductivity observed in the pure salt systems at 25°C was 7 x 10 S cm-1. An electrochemical window of stability of up to 5V was measured on graphite electrodes. The effect of salt structure and solvent on conductivity of the salts is also discussed. 

Fig. 8.3 The lithium—silicon phase diagram. (By permission of the Journal of the Electrochemical Society R.A. Sharma and R.N. Seefurth, 1976, 123, 1763.)...

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