Chronopotentiogram: current step

In spite of its implicit character, this expression is useful for kinetic purposes as it enables us to calculate kf(E) for any point on a measured E, t curve (the chronopotentiogram), being the response to a current step perturbation. 

Chronopotentiometry is the electrochemical technique in which a current step is impressed across an electrochemical cell containing unstirred solution [1-5]. The resulting potential response of the working electrode versus a reference electrode is measured as a function of time (thus, chronopotentiometry), giving a chronopotentiogram as shown in Figure 4.3. 

Cyclic chronopotentometry — A controlled current technique where the applied - current step is reversed at every transition time between cathodic and anodic to produce a series of steps in the potential vs. time plot - chronopotentiogram. The progression of transition times is characteristic of the mechanism of the electrode reaction. For example, a simple uncomplicated electron transfer reaction with both products soluble and stable shows relative -> transition times in the series 1 0.333 0.588 0.355 0.546 0.366... independent of the electrochemical reversibility of the electrode reaction. 

Fig. 9 Response to a current step for a reversible system, illustrated as an oxidation (a) chronopotentiogram and (b) plot of vs Ig...

Chronopotentiometry is a controlled-current technique in which the potential variation with time (0 is measiued following a current step. Other ciurent perturbations such as linear, cyclic, or current reversals are also used [1,3,4,12]. For a reversible electrode reaction following a ciurent step, chronopotentiograms shown in Fig. 7 can be obtained. 

In order to further determine where the products of the reduction waves are soluble or insoluble, inverse chronopotentiometric runs were performed for the two waves. It was shown that the first step proceeds reversibly giving a product which is soluble in the temperature range 700-800 °C. Figure 4.7.1 shows a chronopotentiogram with current inversion, typical of the behaviour of the Pt/NaCl-KCl-NaF-K2TiF6 interface in the potential range corresponding to the second reduction step. 

A second step also appears on chronopotentiograms for the anodic process in highly dilute solutions of riboflavin, where one wave is obtained on the polarogram, but this step occurs in an even narrower range of current densities ( rom 32 to 27 mA/cm ). The second step can be observed with i < 27 mA/cm (27-19 mA/cm ) by increasing the life of the suspended drop at the starting potential from 4 sec (in all the chronopotentiometric measurements) to 30-40 sec. 

Pb +, Zn +, and UOI in molten KSCN was studied polarographically and chronopotentiometrically by Yanagi and co-workers.Well-defined and reproducible chronopotentiograms for the reduction of Cd-, Pb +, and Zn + were obtained the product of current density and the square root of the transition time was proportional to concentration for each system. The reduction of Pb + and Zn + was found to be reversible. The diffusion coefficients reported were of the order of 10 cm-/sec. Two reduction steps were observed for UO + polarographically and chronopotentiometrically. The processes are diffusion controlled and were proposed to be UO2+ + U02 + UOg. The diffusion coefficient of UO ... 

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