Electrode-potential measurement

Pourbaix, M., Recent Applications of Electrode Potential Measurements in the Thermodynamics and Kinetics of Corrosion of Metals , Corros., 25, 267 (1969) de Nora, O., Gallone, P., Traini, C. and Meneghini, G., On the Mechanism of Anodic Chlorate Oxidation , J. Electrochem. Soc., 116, 147 (1969)... 

Pourbaix, M., Recent Applications of Electrode Potential Measurements in the Thermodynamics and Kinetics of Corrosion of Metals , Corrosion, 25, 267 (1%9)... 

Equation (22) shows that since electrode potentials measure electronic energies, their zero level is the same as that for electronic energy. Equation (22) expresses the possibility of a comparison between electrochemical and UHV quantities. Since the definition of 0 is6 the minimum work to extract an electron from the Fermi level of a metal in a vacuum, the definition of electrode potential in the UHV scale is the minimum work to extract an electron from the Fermi level of a metal covered by a (macroscopic) layer of solvent. ... 

Figure 26. Dependence of function 4K.AU) [relation (19)] and of /

Knowledge of the Volta potential of a metal/solution interface is relevant to the interpretation of the absolute electrode potential. According to the modem view, the relative electrode potential (i.e., the emf of a galvanic cell) measures the value of the energy of the electrons at the Fermi level of the given metal electrode relative to the metal of the reference electrode. On the other hand, considered separately, the absolute value of the electrode potential measures the work done in transferring an electron from a metal surrounded by a macroscopic layer of solution to a point in a vacuum outside the solotion. ... 

However, the electrode potentials measured for different types of electrolytes cannot quantitatively be compared with each other, even when the same reference electrode has been used throughout. This is due to the fact that the potential differences at interfaces between dissimilar electrolytes cannot be determined experimentally. For this reason the electrode potentials are measured separately for each type of electrolyte medium. 

The value of p defined by Eq. (29.6) is sometimes called the absolute electrode potential measured against vacuum. We must remember here that we are concerned with electrochemical potentials stated in electron volts rather than with electrostatic potentials stated in volts. Hence, this absolute potential, which can be determined... 

Fig. 5.15 Basic circuit for the electrode potential measurement during current flow A is working (indicator, test), B, auxiliary and R, reference electrode connected by means of the Luggin capillary (arrow) and P, potentiometer. 

Electrode potential measured in solutions where all reactants and products are at unit activity (p. 231). Theoretical Cell Potential... 

The experiments were performed at a constant inflow concentration of ascorbic acid ([H2A]) in the CSTR. Oscillations were found by changing the flow rate and the inflow concentration of the copper(II) ion systematically. At constant Cu(II) inflow concentration, the electrode potential measured on the Pt electrode showed hysteresis between two stable steady-states when first the flow-rate was increased, and then decreased to its original starting value. The results of the CSTR experiments were summarized in a phase diagram (Fig. 6). 

The electrode potential measured at an electrode relates to the Coulomb potential energy V seen by the electrode due to the ions in solution. V relates to two charges zi and z2 (one being the electrode here) separated by a distance r, according to... 

Figure 4-29 iUustrates the relationship for a gold electrode (a) between the electrode potential E measured in aqueous solution hy a conventional method before the emersion and the electrode potential - measured in wet nitrogen... 

Formal electrode potential, An electrode potential measured at STP, in which all reagents and products are present at unit concentration. 

Data from electrochemical impedance diagrams yield a simplified quantitative analysis for an appropriate interpretation of the linear sweep voltammetry (LSV) experiments. In fact, the Si electrode potential measured with respect to the reference electrode represents the value within the bulk of the material. The direct current flow for the electrochemical reaction has to overcome the resistance of the space charge layer, which can reach extremely high values when a depletion layer is formed. For p-type Si in the potential range for the HER onset, this excess surface resistance is over 10 f2 cm. Thus, even with a bias of —1 V, the DC... 

By international convention, a standard electrode potential measures the tendency for the reduction process of an electrode. 

Section 5.2 provides the thermodynamic basis for predicting whether or not a specific redox transformation can occur spontaneously in a given environment. The necessary redox halfreactions involving contaminants are usually well characterized because contaminants are the primary motivation for many studies of environmental systems. However, difficulties often arise in selecting the appropriate "environmental" half-reaction with which to balance the overall equation. When an environmental half-reaction cannot be identified, it is tempting to use traditional electrode potential measurements (127,128) as a generic measure of in situ redox conditions. These values (Emeas) then might be used as E°red or E°ox in Equation 14, to assess the thermodynamic potential of a particular contaminant transformation in a particular environment. However, a number of fundamental difficulties arise with this approach, so we do not recommend the procedure. 

If the Nernst equation is applied to more concentrated solutions, the terms in the reaction quotient Q must be expressed in effective concentrations or activities of the electroactive ionic species. The activity coefficient y (gamma) relates the concentration of an ion to its activity a in a given solution through the relation a = yc Since electrode potentials measure activities directly, activity coefficients can be determined by carrying out appropriate EMF measurements on cells in which the concentration of the ion of interest is known. The resulting Es can then be used to convert concentrations into activities for use in other calculations involving equilibrium constants. 

During surface reactions the substrate, the intermediates, or both, interact strongly with the electrode and diffusion is restricted. The reactions of intermediates generated under these conditions can be expected to differ substantially from those in homogeneous solution. Electrode potentials measured under such conditions cannot be equated to thermodynamic potentials for the formation of the intermediates. Likewise, it is not possible to make kinetic measurements on the reactions of the intermediates which give information relating to the homogeneous solution chemistry. 

Both derivative CV and SHAC voltammetry require specialized instrumentation. A much more simple experimental procedure has been described for electrode potential measurements which can be done with respectable precision using rudimentary instrumentation. The measurement of peak potentials during LSV is normally carried out to a precision of the order of 5 mV. This is because the peak resembled a parabola with a rather flat maximum. On the other hand, the half-peak potential where the current is half the peak value, has just as much thermodynamic significance and can be measured to about 1 mV using x-y recording with a suitable expansion on the potential axis. When used in conjunction with a digital data retrieval system the method is as precise as derivative cyclic voltammetry (Aalstad and Parker, 1980). 

Metal-Metal BDEs from Redox Equilibrium and Electrode Potential Measurements... 

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