Chronopotentiometry, adsorption

Cyclic voltammetry (adsorption, monolayers) Potentiodynamic polarisation (passivation, activation) Cathodic reduction (thickness) Frequency response analysis (electrical properties, heterogeneity) Chronopotentiometry (kinetics)... 

The possibility that adsorption reactions play an important role in the reduction of telluryl ions has been discussed in several works (Chap. 3 CdTe). By using various electrochemical techniques in stationary and non-stationary diffusion regimes, such as voltammetry, chronopotentiometry, and pulsed current electrolysis, Montiel-Santillan et al. [52] have shown that the electrochemical reduction of HTeOj in acid sulfate medium (pH 2) on solid tellurium electrodes, generated in situ at 25 °C, must be considered as a four-electron process preceded by a slow adsorption step of the telluryl ions the reduction mechanism was observed to depend on the applied potential, so that at high overpotentials the adsorption step was not significant for the overall process. 

Chronopotentiometry. Paunovic and Oechslin (8) measured the adsorption of peptone on lead-tin alloy electrodes using chronopotentiometric and double-layer measurements. This case is different from the adsorption of HCOOH because peptone is not an electroactive species in the conditions smdied but only blocks the surface used for the electrodeposition of lead-tin alloys from solutions containing Sn and Pb ions. Chronopotentiometric analysis is based on the following principles (7). In the absence of adsorption, the relationship between the transition time r (for reduction of Sn and Pb in this case), the bulk concentration c° of the substance reacting at the electrode, and the current I is given by the equation... 

Chronopotentiometry, galvanostatic transients, 1411 as analytical technique, 1411 activation overpotential, 1411 Clavilier, and single crystals, 1095 Cluster formation energy of, 1304 and Frumkin isotherm, 1197 Cobalt-nickel plating, 1375 Cold combustion, definition, 1041 Cole-Cole plot, impedance, 1129, 1135 Colloidal particles, 880, 882 and differential capacity, 880 Complex impedance, 1135 Computer simulation, 1160 of adsorption processes, 965 and overall reaction, 1259 and rate determining step, 1260... 

A very important feature of chronopotentiometry is the characteristic variation in ix1/2 that occurs for certain electrode reactions when i is varied over a wide range by varying i. The behavior of ix1/2 can be effectively used to diagnose certain mechanisms of electrode reactions. Diagnostic curves for ix1/2 versus i are shown in Figure 4.4 for several mechanistic situations. A constant value of ix1/2 over a wide range of x (Fig. 4.4A) is characteristic of an uncomplicated, diffusion-controlled electrode reaction with no kinetic or adsorption phenomena at a planar electrode. 

Current-reversal chronopotentiometry is also useful for detecting adsorption of the product generated during the forward electrolysis time. Complete adsorption of the product on the electrode surface causes tr to equal tf since no product is lost by diffusion from the electrode. This approach has been used to determine the amount of adsorbed material formed during the reduction of riboflavin and the oxidation of iodide [10]. 

In general, chronopotentiometry consists of the application of a programmed current function to an electrode, the potential of which is measured as a function of time [13]. Thus the current program may be any function that is electronically feasible. Examples of potentially useful current functions (in addition to those described in preceding sections) are ramp current chronopotentiometry for the elucidation of adsorption mechanisms, and square-root-of-time current chronopotentiometry for which concentration is directly proportional to the transition time ... 

Analyses of insertion electrodes include structural analysis by XRD, neutron diffraction, HRTEM with electron diffraction, chemical analysis by EDAX, XPS and dissolution followed by ICP, morphological analysis by electron microscopy, surface area measurements by gas adsorption, and electrochemical analysis by voltammetry chronopotentiometry (primary techniques) and fine electrochemical tools such as EIS, PITT, GITT, and... 

Transient technique — A technique whose response is time dependent and whose time dependence is of primary interest, e.g., -> chronoamperometry, -> cyclic voltammetry (where current is the transient), -> chronopotentiometry and -> coulostatic techniques (where voltage is the transient). A transient technique contrasts with steady-state techniques where the response is time independent [i]. Some good examples are cyclic voltammetry [i, ii] (fast scan cyclic voltammetry), the indirect-laser-induced-temperature-jump (ILIT) method [iii], coulostatics [i]. The faster the transient technique, the more susceptible it is to distortion by -> adsorption of the redox moiety. 

Similar situation arose in the system of HfCl4-NaCl-KCl. Two steps were recorded at higher concentrations of HfCl4. The plot of /r( ) had a positive slope for the first step, and negative for the second step. Only at high current densities (chronopotentiometry) and at high scan rates (LSV) did the plot indicate an uncomplicated diffusion process. It was concluded that the adsorption of either Hf(II) or Hf(I) species caused the inactivation of the intermediates. 

Riso, R. D. Waeles, M. Pemet-Coudrier, B. Corre, P. Determination of dissolved iron (m) in estuarine and coastal waters by adsorptive stripping chronopotentiometry (SCP). Anal. Bioanal. Chem. 2006, 385, 76-82. 

Table 8. Chronopotentiometry for adsorption studies at stationary electrodes...

A Bads (I ) B Bads- The sequence of these processes is indicated by arrows in the second column GS galvanostatic technique, CR current reversal method and x[j. transition times before resp. after the current reversal surface excess of reactant A at t = 0 reversal time tr < Tjr is considered. Further (a) reaction (I) starts after the total depletion of Aads> (t>) the rates of parallel reactions (I) and (II) depend on the ratio F /cJ (c) valid for F /cJ- O (d) for Fa/cJ- oo. Information about adsorption effects in chronopotentiometry is summarized in [224], principles of the method are discussed in chapter 3, section 3. 

Chronoamperometry, Chronocoulometry, and Chronopotentiometry, Fig. 4 Chronocoulometric charge versus (time) plot in the absence (1) and in the presence (2) of adsorption. The dashed, horiztmtal line represents the charge response in the absence of reactant. This representation is sometimes referred to as Anson plot in the literature... 

Chronoamperometry, Chronocoulometry, and Chronopotentiometry, Fig. 6 dnonocoulometiic plots for double-step experiments. Lines 1 and 2 eoiie-spond to the case when no adsorption of the reactant or product occins. Lines 3 and 4 depict the linear responses when the reactant is adsorbed... 

Before attempting to measure diffusion coefficients, some basic information regarding the electrochemical behavior of the redox species must be known. This is particularly important for newly prepared compounds. First, one should evaluate the reversibility of the electron transfer reaction. Certain techniques, such as LSV, can only be applied to measure diffusion coefficients for nemstian systems. Second, the presence of any coupled homogeneous reactions should be established. The current for each technique is often dependent on such reactions, thus making measurements of the diffusion coefficient unreliable. Finally, the adsorption of reactants or products can produce faiadaic current that can greatly affect the measurement of the diffusion coefficient. For example, measuronent of the critical time in chronopotentiometry is less reliable when adsorption is present For these reasons, the electrochemical behavior of the compound must be factored into the selection of a technique. 

Chen L, Lv C, Chen J, Bi S (2013) Numerical simulation study on cyclic redpiocal derivative chronopotentiometry of reversible electrode reaction coupled with Langmuir adsorption. Electrochim Acta 93 222-229... 

Fekner Z (2008) Eligital simulation of cyclic chronopotentiometry turd reciprocal derivative chronopotentiometry for linear adsorption systems. Collect Czechoslov Chem Commun 73 201-228... 

Fig. 9.1 Dr. Alexander Borisovich Ershler (1935-1989) with his group. From right Dr. chem. A.B. Ershler, Ph.D. phys. Eduard M. Podgaetskii, Engr. Tatyana S. Orekhova, Ph.D. chem. Ida M. Levinson another member of the group, postgraduate student Vladimir Kurmaz, was drafted at this time into the Soviet army. Areas of research adsorption theory of neutral organic compounds and its influence on kinetics of electrode reactions, electrode reactions of organomercury compounds, development of new electrochemical methods (high-speed pulse chronopotentiometry, electroreflection, and optical transitions at the metal-electrolyte interface, etc.). ELAN, 1975...

The electrochemical reduction of Bi - in AlClg-NaCl melts (52-63 mole % AICI3) has been studied by voltammetry, linear sweep voltammetry, and chronopotentiometry at solid electrodes. Torsi and Mamantov found that Bi + is reduced reversibly to Bi" further reduction of Bi+ to Bi is complex and involves intermediate oxidation states which were not characterized electrochemically. Strong adsorption of Bi " at gold and platinum electrodes was observed. As in other systems,the lower oxidation states were found to be more stable at lower temperatures and in more acidic melts. 

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