Potentiostatic experiments

V vs. Ag/AgCl were collected as functions of decomposition time. The electrode potential was initially held at 0.75 V to produce a clean Pt(lll) surface, and was next switched to monitor the CO uptake. Starting at Os, where CO adsorption (from HCOOH decomposition) had not yet begun, the potentiostatic experiment lasted until about 500 s of the progress of reaction. The spectral position is typical of the... 

On the other hand, during potentiodynamic formaldehyde oxidation (solid line in the upper panel of Fig. 13.3b), there is only a small faradaic current at 0.6 V in the positive-going scan, in contrast to the much higher steady-state value (about 0.55 mA) attained in the potentiostatic experiment. 

A second, easier method to follow is based on the fact that in the potentiostatic experiment on Ox at long times n + n2 electrons have passed so that the current is purely diffusive. Therefore, by the use of such current values, recalling that i is proportional to t l/2 for diffusive processes, one can determine the values of id at the various times of interest. 

In a potentiostatic experiment, E is held constant so that, according to eqn. (170), the rate of the electrode reaction depends only on the surface concentrations of the species O and R. One of the simplest circumstances that can be imagined would have the reaction occurring bidirectionally with the forward rate proportional to the concentration of O and the backward rate proportional to the concentration of R, so that... 

Potentiostatic experiments are more often carried out than galvanostatic ones, so that most of the time, for i, an expression is desired in function of the potential. Starting from Equation 1.45, one can deduct a comparison for this ... 

As described in section 2.4.2, an impedance experiment involves the application of an electrical signal (E or O) and the measurement of an electrical current or a potential. Consider that a potentiostatic experiment (application of a potential) with three types of input signals can be used for determination of the impedance49. 

Figure 22. Variations in the current trace in a potentiostatic experiment for an EC sequence for different values of the dimensionless chemical rate constant k0 (numbers on the curves).

In 1931, Muller [43] explained the formation of a porous, insoluble, and poor conducting film by means of a simplified model based on potentiostatic experiments. In this way, it was considered that film formation occurs through the following simple, fast reaction ... 

If the radiolytic species of interest has a fairly long lifetime, then a potentiostatic experiment will yield a Cottrell-like response after the pulse, because the faradaic current is controlled by diffusion, or possibly in part by the electrode kinetics. Data for this case are shown in Figure 18.3.4. The radiolytically generated radical of ascorbic acid decays on a millisecond time scale. Current transients following separate radiolytic pulses were recorded for different potentials, and samples were taken at a fixed delay time to produce the sampled-current voltammogram displayed in Figure 18.3.4. 

In the early potentiostatic experiments by Devanathan and Stachurski [98], the time required for the subsurface concentration to become constant, as assumed, was treated simply as a shift in the timescale at the beginning of a permeation curve. However, the permeation behavior for the constant concentration case and that in which the... 

Whether the total corrosion process is determined by the kinetics of anodic metal dissolution or the cathodic process depends on the size of the cathode and the kinetics of the partial electrode processes. The slowest reaction is the rate-determining step, as is usual in kinetics. In the case of a well-passivated valve metal, this is most probably the cathodic reaction, whereas for metals with semiconducting oxides, the rate-determining step win he anodic metal dissolution. In order to study the partial reactions of pitting corrosion separately, potentiostatic experiments are preferred. The cathodic process is replaced hy the electronic circuit of the potentiostat to investigate the anodic metal... 

Potentiostatic pitting experiments have a characteristic current-time curve. During the early stage of pit growth, the nominal current density increases with the second or third order of time [8, 14, 15], whereas in later stages a square root time law may be observed. These time laws are a direct consequence of a local pit current density ipit that is constant or decreases with time and a constant number of corrosion pits or a constant nucleation rate. A constant /pit corresponds to a linear growth of the pit radius dr/dr. The surface of a hemispherical pit increases with r. If all pits start at the beginning of a potentiostatic experiment, one obtains a second-order law, / = a t. ... 

M. Ilieva and V. Tsakova, Copper modified poly(3,4-ethylenedioxythiophene) Part I. Potentiostatic experiments, Synth. Met., 141, 287 292 (2004). 

Critical initiation potentials can be defined by means of potentiostatic experiments with crevice specimens, e.g. as shown in Figure 7.24 [7.19, 7.20]. Possible initiation of crevice corrosion (at a given set potential) is indicated by a marked increase in the... 

Estimated current efficiencies obtained from potentiostatic experiments (+600 mV for 3h) after current-time integration coupled with the determination of total copper dissolved (by AAS) were 100 3 % for reaction (11) and 99 3 % for reaction (12). ... 

The current decreases to the point of reaching zero. Here in such a system it is impossible to attain a steady state with a current that is anything other than zero. In a potentiostatic experiment, the only steady state that can be observed is therefore the equilibrium state with zero-current. This equilibrium state eventually settles once the transient current flow has homogenized the electrolyte composition. This composition correlates with the potential imposed at the working electrode, according to the Nernst law. 

In order to allow the current flow through the film of the CP, a metallic counter-electrode (CE) immersed in the electrolyte (Figure 16.10) is required. The use of a reference electrode (RE) allows perfect control of the CP potential (potentiostatic experiment), providing the potentiostat with the flow of the... 

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