Current potential characteristic

The quality and quantity of sites which are capable of reversible lithium accommodation depend in a complex manner on the crystallinity, the texture, the (mi-cro)structure, and the (micro)morphology of the carbonaceous host material [7, 19, 22, 40-57]. The type of carbon determines the current/potential characteristics of the electrochemical intercalation reaction and also potential side-reactions. Carbonaceous materials suitable for lithium intercalation are commercially available in many types and qualities [19, 43, 58-61], Many exotic carbons have been specially synthesized on a laboratory scale by pyrolysis of various precursors, e.g., carbons with a remarkably high lithium storage capacity (see Secs. 

Very little can be concluded form the experimental results with respwt to theoretical current-potential characteristics in the dark and under illumination derived in the previous chapter. Since in none of these cases a complete i-U-curve was pubhshed or... 

Figure 7.7 Current-potential characteristics for a redox reaction via the conduction band or via the valence band. The current was normalized by setting jo = 1- In this example the redox system overlaps more strongly with the conduction than with the valence band.

Figure 7.9 Current-potential characteristics for an n-type semiconductor in the dark and under illumination. The difference between the two curves is the photocurrent.

The current-potential characteristics of a redox reaction can thus be measured in the following way An overpotential rj is applied, and the current is measured for various rotation rates in. From a Koutecky-Levich plot the corresponding kinetic current jk(rj) is extrapolated. This procedure is repeated for a series of overpotentials, and the dependence of jk on rj is determined. 

The data shown in Figure 2.36 were gathered at constant current with a value of the current density that brought the electrode potential at the foot of the current-potential characteristic of the system. The concentration of substrate may thus be considered as constant. As discussed in Section 2.5, we consider only the case where the second electron transfer in the radical-substrate coupling pathway occurs at the electrode (ECE). The following equations and conditions apply. 

The experimental practice for the study of current/potential characteristics requires the formation of an ohmic contact on the back of the electrode. The simplest technique consists in the application of a very thin layer of Ga—In eutectic liquid alloy, which wets the surface easily. But in the most rigorous method used in production lines, a highly doped 750-nm... 

The formalism developed to describe current-potential characteristics for the Cd(II)/Cd(Hg) multistep electrode... 

A solar cell was constructed from a p—fCH- film and a single crystalline n-Si wafer. The current-potential characteristic of the battery is shown in Fig. 20 73). A conversion efficiency of 4.3 % was obtained. The most sincere problem for poly-(acetylene) is its instability against air oxidation. If it could be solved, practical use of light weight and easily moldable solar cell from polymer films might be possible. 

However, it should not be surprising if the anodic and the cathodic Tafel plots do not intersect at E = Ecorr as the two reactions participating in the corrosion process are actually studied at potentials far removed from the corrosion potential. Moreover, it is not quite realistic to rely on the very simple model described here. Therefore, it appears more useful to record a complete current-potential characteristic and to attempt its interpretation in terms of simultaneous processes that can possibly be expected. Several practical examples have been extensively reviewed [93]. 

If the electrode reaction proceeds via a non-linear mechanism, a rate equation of the type of eqn. (123) or (124) serves as a boundary condition in the mathematics of the diffusion problem. Then, a rigorous analytical derivation of the eventual current—potential characteristic is not feasible because the Laplace transfrom method fails if terms like Co and c are present. The most rigorous numerical approach will be... 

Figure 8. Current-potential characteristics of CdSe/h + RbAgJs interface under chopped illumination (voltage scan rate 40 mV/s)...

The presence of dissolved molecular oxygen favors recombination of photogenerated charge carriers in Ti02 particles [40]. In agreement with this, a typical current-potential characteristic of Ti02 thin layers (particle size about 10 nm) is shown in Fig. 5.13. 

Fig. 5.13. Current-potential characteristic of a nanostructured FT0/Ti02 thin layer in 0.5 M...

The existence of bistability in the //under conditions under which chemical variable, on which the current depends, exhibits bistability as a function of DL. Thus, in S-NDR systems we have to require that the dynamic equations contain a chemical autocatalysis. As set forth below, m takes the role of the negative feedback variable. The positive feedback might be due to chemical autocatalytic reaction steps as is the case in Zn deposition [157, 158] or CO bulk oxidation on Pt [159], S-shaped current-potential characteristics may also arise in systems with potential-dependent surface phase transitions between a disordered (dilute) and an ordered (condensed) adsorption state due to attractive interactions among the adsorbed molecules. 

FIGURE 3 Steady-state current-potential characteristics of an n-type GaN/Pt electrochemical cell under dark and illuminated etching conditions [26],... 

The dependence of the Gibbs free energy pathway on electrode potential (Figure 3.3.10A) manifests itself directly in the experimental current potential characteristic illustrated in Figure 3.3.10B. At 1.23 V, no ORR current is measureable, while with decreasing electrode potentials the ORR current increases exponentially until at +0.81 V, processes other than surface kinetics (e.g. mass transport) begin to limit the overall reaction rate. Figure 3.3.10B represents a typical performance characteristic of a Pt or Pt-alloy electrocatalyst for the ORR. 

Fig. 23M Current-potential characteristic of a system undergoing passivation. The optimum potential region for anodic protection is shown. E - breakdown potential, E - repassivation poten-...

Figure 29. Calculated current-potential characteristics for direct (dashed lines, 0/cm ) and surface state mediated electron transfer between an -type semiconductor electrode and a simple redox system. The plots show the transition from ideal diode behavior to metallic behavior with increasing density of surface states at around the Fermi-level of the solid (indicated in the figures). This is also clear from the plots below, which show the change of the interfacial potential drop over the Helmholtz-layer (here denoted as A(Pfj) with respect tot the total change of the interfacial potential drop (here denoted as A(p). Results from D. Vanmaekelbergh, Electrochim. Acta 42, 1121 (1997).

In order to discuss the correlation between etching kinetics and etching morphology, let us first reconsider the current-potential characteristics of III-V semiconductors, as depicted in Fig. 1. For the sake of clarity, the behavior in alkaline solutions (Fig. 1 (b)) is treated first. As announced, the discussion is mainly based on experimental results obtained from GaP single crystals. 

Fig. 9. Current potential characteristics obtained with the cell in Fig. 7 at several temperatures in a water-vapor-saturated oxygen atmosphere [9], (Reprinted by permission of the Electrochemical Society).

Fig. 33. Cathodic current-potential characteristics (curves on the left) for pure iron, and iron bombarded with Au and Pb respectively, iq are the corresponding corrosion current densities...

In these situations the current flow is entirely controlled by the kinetics of the heterogeneous electron transfer, which is then said to be slow or irreversible. The current-potential characteristic of the redox couple under study then reflects thermodynamic (E°) and kinetic (k ) properties. Indeed, the driving force E — E° is used to overcome not only thermodynamic but also kinetic limitations. 

Yet because of the chemical reaction, the activity of P at the electrode surface is considerably decreased. From Eq. (122) it is seen that the electrode potential is then positive (for a reduction negative for an oxidation) to that observed for the same current density, but in the absence of the follow-up reaction. As a result the current-potential characteristic is observed in a potential range positive to E° for a reduction and negative to E for an oxidation. The system is then said to be nernstian and chemically irreversible. 

Fig. 39 Current-potential characteristics obtained a water vapor-saturated oxygen atmosphere [59].

Insertion of these relationships into Eqs (2) and (4) yields the complete current-potential characteristic, j, [7] ... 

Meissner D. and Memming R. (1992), Analysis of current potential characteristics at n-type andp-type semiconductor electrodes , Electrochim. Acta 37, 799-809. 

The formalism developed to describe current-potential characteristics for the Cd(II)/Cd(Hg) multistep electrode reaction [47] was used for the investigation of catalytic and inhibiting influence connected with variation of electrolyte composition. 

Fig. 7,10 Current-potential characteristics for n- and p-GaAs electrodes in 0.1 M H2SO4...

The steady states of Eq. (1) [i.e., the solutions of Eq. (1) with d ijdt = 0] can be easily obtained graphically by plotting the characteristics of the external circuit, the load line, and the current-potential characteristics of the electrode/electrolyte interface in one graph [Fig. 2(a)]. Obviously, intersections of both curves are steady states or fixed points of the system, and from Fig. 2(a) it becomes immediately clear that whenever the interfacial characteristic is N-shaped, Eq. (1) possesses three stationary states in a certain range of U and Rg. 

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