Electrode potential curves

Current density versus electrode potential curves (current-potential curves)... 

Value of jg depends on selection of part of the current density vs. electrode potential curve. 

The basic theory of mass transfer to a RHSE is similar to that of a RDE. In laminar flow, the limiting current densities on both electrodes are proportional to the square-root of rotational speed they differ only in the numerical values of a proportional constant in the mass transfer equations. Thus, the methods of application of a RHSE for electrochemical studies are identical to those of the RDE. The basic procedure involves a potential sweep measurement to determine a series of current density vs. electrode potential curves at various rotational speeds. The portion of the curves in the limiting current regime where the current is independent of the potential, may be used to determine the diffusivity or concentration of a diffusing ion in the electrolyte. The current-potential curves below the limiting current potentials are used for evaluating kinetic information of the electrode reaction. 

The type of electrode reaction employed, the cell geometry, and the manner in which the limiting-current measurement is carried out determine the shape of the current versus electrode-potential curve. Often the ideal horizontal inflection in such curves is absent, making the determination of true limiting current problematical if not impossible. Characteristics of satisfactory limiting current plateaus are as follows ... 

Figure 8-24 illustrates schematicaUy the transfer reaction currents of redox electrons and redox holes as functions of electrode potential these reaction cur rent versus electrode potential curves are obtained from the formulation of the reaction currents in Eqns. 8-62 through 8-65. 

Figure 4.9 Electrode current versus electrode potential curves for solutions containing O2 (a) in otherwise pure water (b) in the presence of Fe. In (a) the net current is close to zero over a wide range of potential, so it is difficult to locate the equilibrium potential. In (b) the measured equilibrium potential is a mixed potential, Em, obscuring the true equilibrium potential of the system, Feq (Stumm and Morgan, 1996). Reproduced by permission of Wiley, New York...

Figure 1. Photocurrent/electrode potential curves for n-type TiOg single crystal with ohmic-indium contact on hack side. Potentials measured with respect to saturated KCl calomel electrode with a platinum black counter electrode. Light intensity increasing in order 3,2,1. Wavelength, 415 nm or less. Exposed surface of TiOg crystal ((Mil) (10).

Fig.1 Surface concentration of adsorbed ions versus rational electrode potential curves for the Cd(OOOl) electrode in aqueous solution with constant ionic strength O.lx M KA + 0.1 (1 - x) M KF, where A is the surface-active halide ion (Br curves 1-3) and (1 curves 4-6), and x is its mole fractions, x = 0.1 (curves 1,4) ...

FIGURE 9.2 Current density vs. electrode potential curves for the H2-02 and the CH30H-02 fuel cells showing the reaction overvoltages T a and T c at different catalytic electrodes (Pt, Pt-Ru,...). 

Interfacial tension against electrode potential curves have a parabolic shape with a maximum value which depends on the nature and concentration of the electrolyte (see fig. 10.1). Detailed results for the mercury aqueous solution interface were initially reported by Gouy [7, G5]. Examination of these data for the alkali metal halides shows that the interfacial tension depends markedly on the nature of the electrolyte at positive potentials. On the other hand, the variation with electrolyte at negative potentials is rather small. It follows that the anions in the electrolyte strongly affect the interfacial tension when they predominate in the double layer. 

Figure5.2 Electrode potential curves obtained for (a) Lii NiO2 (b) Lii CoO2 (c) Lii 5Mn2O4 and (d) graphite by using the galvanostatic intermittent titration technique. These include changes in the equilibrium phase as lithium intercalation/ deintercalation proceeds. (Reproduced with permissions from (a) Ref. [11] (b) Ref. [14] (c) Ref. [17] (d) Ref. [18].)...

Figure 5.4 represents the electrode potential versus lithium content curve and the plots of (1 — 5)i and (1 — 8)2 with respect to (1 — 8) calculated for the case of U = —4.12 eV, Ji = 37.5 meV (repulsive interaction), J2 = —4.0meV (attractive interaction), and T = 298 K for Lii 8Mn2O4. The theoretical electrode potential curve shows a steep potential drop at (1 — 8) = 0.5, which is typical for ordering of lithium ions due to their strong interaction [15, 20, 22, 23]. The order-disorder phase transition occurs at the boundaries where (1 — 8)1 and (1 — 8)2 begin to deviate severely from (1 — 8) values of approximately 0.15 and 0.85. 

Figure 5.12 (a) Logarithmic cathodic current transients experimentally obtained from the Liq -hs[Ti5/3LiT/3]O4 electrode at the potential drops from 1.700V (versus Li/Li ) to various lithium injection potentials below the plateau potential (b) Cumulative charge versus time plots reproduced from panel (a), along with electrode potential curve of Liq 5 7ri5y3Liqy3]O4. (Reproduced with permission from (a) Ref. [11] (b) Ref. [96].)... 

The solid circles in Figure 5.13a-e denote the initial current levels Jin, at various potential steps A , calculated from the corresponding CTs. Invariably, all of the li i versus A plots show a linear relationship. It should be mentioned that even diffusion-controlled CTs can exhibit this type of linear relationship, in the case that the electrode potential curves vary linearly with lithium stoichiometry, A oc ( -c ). However, the linear relationship between and A is still valid for the electrodes (e.g., Lii + 5[Ti5/3Lii/3[O4, Lii 5CoO2, LisV2O5 and graphite) where the electrode potential versus lithium stoichiometry curves deviate strongly from the linear relationship. 

The model parameters are determined in the following manner the functional relations =/( — 8) and Rincorporated into B.C. of Equation (5.21), are obtained by the polynomial regression analysis of the electrode potential curves and the Kceii versus E curves determined from the Jin, versus AE plots, respectively. It should be borne in mind that (1 — 8) does not represent the average lithium content in the electrode, but the lithium content at the surface of the electrode. In other words, the electrode potential (t) in Equation (5.21) is the potential at the electrode surface. As the relationship —/(I — 8) includes information about the phase transition, we can consider the effect of phase transition on the theoretical CT with the functional relationship =fil — 8), without taking any of the intercalation isotherm. 

C, respectively. None of the electrode potential curves show any potential... 

Figure S.17 The galvanostatic intermittent discharge (electrode potential) curve measured on the PVDF-bonded MCMB800 (0), MCMBIOOO ( ) and MCMB1200 (A) composite electrodes in 1 M LiPFfi-EC/DEC solution. Regions I, II, lll-l, and II1-2 represent the potential ranges necessary for lithium deintercalation from the sites for Type I, II, lll-l, and III-2, respectively. (Reproduced with permission from Ref. [82].)...

At about 813 °C, the equilibrium constants Af, and K2 given by Equations (25-22) and (25-23) are equal. The electrode potential curves for pure water vapor and carbon dioxide (at the same pressure) as well as the curves for the same ratios of H2.H20 and CO,C02, intersect at this temperature (see Figure 25-1). H2 and CO with H2O and COj lead to the same pO and have the same effectiveness in redox reactions in this region of temperature. For this reason 813 °C is recommended as the fixed temperature for the sensor in devices that are to be used to measure combustible gas mixtures [11, 79]. 

The electrode potential curves lie between those for pure H2.H20 and C0.C02 mixtures (Figure 25-1). They are steeper if the proportion of C0.C02 is larger than Hj,H20. 

The electrode potential curve for the equilibrum of pure carbon and a pure C0,C02 mixture (Boudouard-Equilibrium) at a total pressure p is shown in Figure 25-1. This is the border line of all electrode potential curves of pure COfZO mixtures. The plot is linear at low and high temperatures, because the concentration of either CO in comparison to COj or vice-versa can be ignored. In the limiting cases there are the equilibria... 

The electrode potential curves for equilibria with the three pure iron oxides FeO, FcjO and Fe203 are shown in Figure 25-1. Electrochemical measurements yield for the three plots at high temperatures [20] ... 

The regions of stability of the various iron oxides are found between the electrode potential curves. The electrode potential resulting with a gas mixture must lie between these curves, if one wishes to convert iron oxides into this particular state by influence of the gas mixture. 

Figure 1. Electrode potential curves obtained from the (intermittent) galvanostatic charge-discharge curves of the carbon-dispersed composite electrodes of (a) Lii. sNiOa, (b) Lii Co02, (c) Li6V20s, (d) Lii+6[Ti5/3Li /3]04, and (e) graphite. Reprinted from (1999), (2001), and (2001), with permission from Elsevier Science.

On the other hand, it is very interesting that the CTs in Figures 4 and 5 seem to reflect the concavity of the electrode potential curves within the single a phase region the electrode potential curves (Figures lb and c) first fall rapidly and finally slowly in the cathodic direction. In other words, the electrode potential first rises up slowly and finally rapidly in the anodic direction. The rate of change in electrode potential with lithium content in the cathodic and anodic directions equals qualitatively the rate of change of current with time in the cathodic and anodic directions, respectively. 

Figure 15. Inhibition in both oxidizing and nonoxidizing inhibitors. Weight-loss data in aerated solutions. Electrode potential curves in absence of oxygen (13).

Fig. 5.137. Cyclic voltammogram and selected mass intensity vs. electrode potential curves measured during electrooxidation of uric acid at pyrolytic graphite mje 157 = allantoine, m/c 167 = (uric acid - H) , 183 = imine alcohol, based on data in [856]...

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