Chronoamperometric current

Figure 6.11 Stripping chronoamperometric current transients on stepped Rh single-crystal surfaces, (a) Full transients obtained on the four different surfaces at F = 0.65 V (with respect to an RHE), in 0.5 M H2SO4. (b) Initial parts of the transients in (a).

For a quantitative description of the way that a chronoamperometric current trails off with time, we employ the Cottrell equation, as follows ... 

Figure 2.22 Chronoamperometric current transients (dotted lines) and probe-beam deflection transients (solid lines) during the oxidation-reduction cycles of (PAH-Os)t5(PSS)- 4 PEM film in 10 mM HCI solution. Panels A-D show consecutive oxidation-reduction steps with a wait time of 180 s at the end of each train in the reduced state. Taken from Ref. [28].

Figure 17.4 Current-potential curves constructed from chronoamperometric current-time data recorded at a platinum electrode in a 3.34 x 10 2 M solution of Ti(II) in the 65-35 mol% AlCl3-NaCl melt at 185°C. [From K. W. Fung and G. Mamantov, J. Electroanal. Chem. 35 21 (1972), with permission.]...

Figure 32. Amperometric response of rotating Cat/NiO modified GC electrode to H202, conditions -0.3 V constant potential, pH 7.0 and rotation speed is 2000 rpm, (A) successive addition of lOOpM and (B ) 1 liM insets plot of chronoamperometric current vs, H202 concentration and linear calibration curve for determination of KM. Reprinted from Biophysical Chemistry, 125, A.Salimi, E. Sharifi, A. NoorBakhash, S. Soltanian, Direct electrochemistry and electrocatalytic activity of catalase immobilized onto electrodeposited nano-scale islands of nickel-oxide, 546, Copyright( 2007), with permission from Elsevier.

It is well known that when mass transport is purely controlled by the reaction diffusion in the electrode or electrolyte, the electrochemical responses at the rough interface obey the generalized form of the Cottrell equation. For certain cases, however, classical fractal behavior under diffusion-controlled constraint is replaced by mixed kinetic/diffusive control (de Levie and Vogt, 1990 Kant and Rangarajan, 1995 Jung and Pyun, 2006a,b). Taking oc = (dp - l)/2, the chronoamperometric current becomes (Dassas and Duby, 1995 Stromme et al., 1995 Andrieux and Audebert, 2001) ... 

In several cases, when the electrocatalytic pathway involves adduct formation between immobilized units of the catalyst and the mobile substrate permeating the porous solid, the mechanism can be described in terms of a charge transfer process preceded by a relatively slow chemical reaction. Here, the chronoamperometric current can be approached by (Koutecky and Brdicka, 1947 Bard and Faulkner, 2001) ... 

The case of charge transfer process preceded by a first-order bulk-surface reaction has been described by Guidelli (1971). Here, the parent electroinactive species is transformed into an electroactive species both through a homogeneous chemical reaction taking place within a thin solution layer adjacent to the electrode (with rate constant, Ay) and through a heterogeneous chemical reaction catalyzed by the electrode surface (with rate constant The chronoamperometric current becomes ... 

Figure 3-4. (A) Surface reconstitution of apo-glucose oxidase on a PQQ-FAD monolayer associated with an Au-electrode. (B) Cyclic voltammograms corresponding to (a) the reconstituted glucose oxidase monolayer in the absence of glucose, and (b) in the presence of glucose, 80 mM. Data recorded in 10 mM phosphate buffer, pH 7.0, at 35°C, scan rate 5 mV s . Inset Calibration curve corresponding to the chronoamperometric currents atE = 0.2 V at different glucose concentrations. Reproduced with permission from ref. 31. Copyright 1996 American Chemical Society.

The increased current tailing at longer times along with a shift of the current peak to longer times found in kMC simulations with low CO surface mobility, cf. Figure 2.4a, is characteristic for experimental transients on small nanoparticles ( 1.8 nm). Overall, the simulated transients capture all the essential features of experimental current transients. Analogous as for large nanoparticles, the model fits chronoamperometric current transients for various potentials and, thereby, explore effects of particle size and surface structure on rate constants, Tafel parameters (transfer coefficients), and equilibrium potentials. Due to the stochastic nature of the MC approach, systematic optimization of the fits is a much more delicate task. 

D. Shoup and A. Szabo. Chronoamperometric current at finite disk electrodes, J. Electroanal. Chem. 140, 237-245 (1982). 

At long times, when (Df) > L = F/c, where L is the film thickness, the concentration within the surface film impacts on the film-solution boundary, the chronoamperometric current will be less than that predicted by the Cottrell equation. 

That means that the chronoamperometric current on the microdisk electrode quickly acquires a limiting value ... 

Fig. 8. Oxidation current from a microvoltammetric electrode placed in the caudate nucleus of an anesthetized rat during an electrical stimulation of the medial forebrain bundle. Top chronoampero-metric current ya. time at 0.5 V ys. SCE. Bottom difference of voltammogram obtained at the peak (circles), compared to voltammograms obtained for dopamine (DA) and ascorbic acid (AA) in vitro. Current scales for voltammograms i = 16 pA, 25 yM dopamine i = 28 pA, 200 jjM ascorbic acid i 32 pA, stimulation. Insert chronoamperometric current ys. time for an Identical experiment with 2-s intervals between measured points. Reprinted with permission from reference 34 (copyright 1983 by the AAAS).

FIGURE 1.30. Typical chronoamperometric current transients for redox switching obtained for a poIy(aniIine)-coated ultramicro Pt electrode (10-/M. diameter) in 1M HCl. In each case the film was initially reduced at -300 mV for 10 minutes before applying the potential pulse. The step amplitude is indicated in the diagram. 

The shape of the chronoamperometric current response depends to a large extent on the value of the uncompensated solution resistance R . We note from Fig. 1.54 that is in series with the finite transmission line element. The presence of uncompensated solution resistance effects can be clearly identified by examining the current/time data when the latter is plotted in i(t) versus format. In many cases (see Fig. 1.56) such plots are nonlinear, so we observe deviation from the expected linear response at both short and long time periods. At short time... 

Figure 6.1.1.2 shows the chronoamperometric (current-lime) response for a 10 pm radius platinum microelectrode where the supporting electrolyte is aqueous 0.1 M LiC104. This figure shows that current flows for approximately 10 psec due to double-layer... 

Rajendran L, Sangtiiantirayanan MV (1995) A two-point Pade approximation for the nonsteady state chronoamperometric current at ultiamiciodisc electrodes. J Electroanal Chem 392 75-78... 

Senthamarai R, Rajendran L (2008) Analytical expression for trtmsient chronoamperometric current at ultramicroband electrode. Russ J Electrochem 44 1156-1161... 

Szabo A, Cope DK, TaUman DE, Kovach PM, Wightman RM (1987) Chronoamperometric current at hemicylinder and band microelectrodes theory and experiment. J Electroanal Chem 217 417 23... 

Bieniasz LK (2016) Highly accurate, inexpensive procedures for computing theoretical chronoamperometric currents at single straight electrode edges and at single microband electrodes. J Electroanal Chem 760 71-79... 

The active site model was solved for COad monolayer oxidation, and results agree with chronoamperometric current transients that had been measured at various... 

At long times, the concentration profile within the polymer film impinges on the film/solution boundary, i.e., D rld- > 1. The chronoamperometric current will be less than that given by the Cottrell equation analog (Eq. (2a)]. We now have a finite (i.e., bounded) diffusion regime. 

Szabo, A. Cope, D. Tallman, D. Kovach, D. Wightman, P. Chronoamperometric current at hemicylin-der and band microelectrodes—Theory and experiment. J. Electroanal. Chem. 1987, 217,417-423. 

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