Current vs. time

Coulometry. If it can be assumed that kinetic nuances in the solution are unimportant and that destmction of the sample is not a problem, then the simplest action may be to apply a potential to a working electrode having a surface area of several cm and wait until the current decays to zero. The potential should be sufficiently removed from the EP of the analyte, ie, about 200 mV, that the electrolysis of an interferent is avoided. The integral under the current vs time curve is a charge equal to nFCl, where n is the number of electrons needed to electrolyze the molecule, C is the concentration of the analyte, 1 is the volume of the solution, and F is the Faraday constant. 

Fig. 17-1 Protection current vs. time for uncoated steel in a calm sea.

Current vs. time traces show that when UPD potentials from studies on gold are used for a cycle, charges during the first cycle look reasonable, consistent with forming a monolayer of the compound. Subsequent cycles, however, show a steady drop in charges each cycle. After a short time, 10-20 cycles, the currents are insignificant, and no visible deposit is formed. 

FIGURE 1.2. Cyclic voltammetric Nemstian waves for free-moving molecules, a Potential scan for a reduction, b, b Variations of the A ( ) and B (—) concentrations at the electrode surface with time (b) and potential (b ). c, c Current vs. time (c) and potential (c ). d, d Negative charge injected in the solution vs. time (d) and potential (d ). 

The resulting expressions for —jF/F = tijVi + nnvn may be used either to analyze the current vs. time functions at fixed potential [128] or the current vs. potential function, e.g. measured in the normal pulse polaro-gram or the d.c. polarogram [127]. In the latter reference, the mathematics pertaining to the dropping mercury electrode (expanding plane... 

The better accuracy of current vs. potential or current vs. time measurements at controlled potential makes these methods preferable to the chronopotentiometric method. However, at controlled potential, the mathematical evaluation of the requisite relationships is more complex due to the difficult inverse transformation of the terms s 1/2 jF(s) and (s + ki) in jF (s), or the solution of the corresponding convolution... 

The photo-assisted electrolysis current vs. time scans were obtained with the following experimental set-up ... 

Our emphasis in this paper will be to describe and analyze current vs. time scans determined after making stepped-changes in the illumination intensity. These scans were performed after proper photoanode pre-conditioning was indicated. 

Figure 1. Oscilloscope traces of current vs. time response following opening and closing of the lightbox shutter, Type I TiOs photoanode, 7. ON HsSOi ((a) 0.4 V (b) 0.5 V (c) 0.6 V (d) 0.7 V)...

We explore below the hypothesis that the observed overshoot current vs. time behavior arises from this effect. In essence, the time dependent change in IT1" produces an associated change in the barrier height for electron transfer to the semiconductor surface, altering the surface electron/hole recombination rate. 

Bokris and Uosaki (1) have studied transient photo-assisted electrolysis current for systems including a p-type semiconductor photocathode and dark Pt anode. A set of current vs. time scans taken with a ZnTe photocathode system is shown in Figure 6. 

Fig. 11.9. Background current vs. time profiles for (O) anodically oxidized diamond and ( ) glassy carbon electrodes. The applied potential was set at...

Fig. 11.10 Parallel chronoamperometric screening of a 64-element, thin film electrocatalyst library for the oxidation of methanol. The library contained a diverse set of binary, ternary and quaternary electrocatalyst compositions consisting of Pt in combination with W, Ni, Co and Ru. The graph plots current vs. time and channel number. Conditions 1 M methanol, 0.5 M H2S04, room temperature, = + 450 mV/RHE, test time = 5 min. For clarity, channel numbers 2-4,10,12,19, 20, 23, 26-29, 42,45 and 57 are omitted. (Reproduced from [18]).

The exciton migration within aggregates of cyanine dyes and the possibility of oxygen diffusion into the porous dye film result in a bulk generation of photocurrent [80]. Photoholes produced due to the oxidation of excitons by molecular oxygen diffuse to the back contact. The diffusion coefficient of charge carriers in dye layer (Dc) can be evaluated from the potential-step chronoamperometric measurements in the indifferent electrolyte. Considering dye film as a thin-layer cell, the current vs. time dependence can be described as follows [81] ... 

Fig. 8.2. Relative error in computed current vs time, narrow scale...

In normal high pressure liquid chromatography, typical sample volumes are 20-200 p.L this can become as little as 1 nL in capillary HPLC. Pretreatment of the sample may be necessary in order to protect the stationary phase in the column from deactivation. By employing supercritical fluids such as carbon dioxide, pretreatment can be bypassed in many instances so that whole samples from industrial and environmental matrices can be introduced directly into the column. This is due to the fact that the fluid acts as both extraction solvent and mobile phase. Post-column electrochemistry has been demonstrated. For example, fast-scan cyclic voltammo-grams have been recorded as a function of time after injection of microgram samples of ferrocene and other compounds in dichloromethane solvent and which are eluted with carbon dioxide at pressures of the order of 100 atm and temperatures of 50°C the chromatogram is constructed as a plot of peak current vs. time [18]. 

For potentiostatic holds between and EM, the current vs. time signal will typically look like Fig. 25a. After the initial decay from a high current, there will be an incubation time during which the current will remain low (e.g., on the order of 1 pA/cm2 or less for stainless steels in neutral solution). Often, transient bursts of current will be observed. These currents are due to the initiation and... 

Figure 3.53 Electrochemical cell employing flexural-wave device as one electrode. Top Cell with RF source to drive platinum-covered flexural-wave device in bottom of cell. Middle Limiting celt current vs time as both transducers on FPW device are switched on and off, producing standing waves, at the different drive amplitudes shown as parameter. Bottom Square-law dependence of increase of limiting current upon transducer voltage that produces mixing of the liquid in the cell. (Reprinted with permission, see Ref. (76). 1991 IEEE.)...

Figure 3. Chronoamperometric curve recorded for an ErQEr mechanism a) plot of current vs time, b) plot of time-normalized current (i ft) vs the logarithm of time, c) plot of number of electrons (n, see text) vs the logarithm of time, and d) plot of n vs logarithm of the dimensionless rate constant (A = k t).

Fig. 49. Current vs. time curves for two different experiments in which a single pit growing under potentiostatic control [9.8 V (Ag/AgCl)] was subjected to flow. Electrode, 304 stainless steel electrolyte, 0.1 m Na2S04, 0.2 M NaCl (pH = 3.5) [98]. Pe = Peclet number. Reproduced from Corros. Scl. 29, 31 (1989) by permission of the Editor.

Figure 6. Current vs. time, and transmittance-decrease vs. time plots for n-heptyl-viologen reduction obtained on a clean (top) and ion-beam modified (bottom) ITO, MPOTE. Current increases with (tinted in the nucleation region, and then decreases, while the absorbance changes linearly. Rates of nucleation are enhanced on the modified surface. [n-HV ] = 10 3M, 0.1 M KHP. Potential steps are indicated with each plot.

Figure 5. Representative current-voltage waveforms [9], Dashed line current vs. time solid line voltage vs. time. (A)R = IkD (B)R = 6.8kD (C)R = lOkfl (D)R = lOOkfl.

Fig. 2. (left) Graph of electrical current vs. time during a CE-NMR thermometry experiment, (right) Corresponding plot of intracapillary temperature vs. time. The peak in the temperature corresponds to the passage of the lower conductivity NaCl solution through the NMR coil. (Reprinted with permission from ref. 24, Copyright 2000 American Chemical Society.)... 

Figure 62. Single autonomous oscillation during Co dissolution, (a) Total current vs. time, (b) Position of the leading edges of the activation waves vs. time. (Reprinted with permission from R. D. Otterstedt, P. J. Plath, N. 1. Jaeger, and J. L. Hudson, Phys. Rev. E 54, 3744, 1996. Copyright 1996, American Physical Society.)...

Figure 65. (A) Video images of a clockwise rotating wave during Co dissolution. (B) Total current vs. time. (C) Potential between the working electrode and an additional reference electrode with a capillary placed at the rim of the working electrode ca. 1 mm away from the surface. (After Otterstedt et al. Reproduced by permission of the Royal Society of Chemistry.)...

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