Potential step methods chronoamperometry

Potential step method Chronoamperometry Chronocoulometry Voltage pulse method Pulse polarography Differential pulse polarography... 

As discussed earlier, the potential is scanned between selected potentials with the measurement of the corresponding electrical current. Another type of electrochemical methods is potential step methods, such as chronoamperometry. In this case, the potential of the working electrode is changed drastically and immediately from a potential Ex to a potential E2, at the... 

The potential step methods are called chronoamperometry and like LSV and CV can deal with only the forward process (single step) or with the reverse process, involving the primary intermediate, as well. The latter is called double potential step chronoamperometry (DPSC) and is by far the most useful in kinetic studies. The applied potential-time wave form as well as the currenttime response for a reversible electrode process are illustrated in Fig. 3. The potential is stepped from a rest value where no current flows, usually 200-300 mV from the potential where the process of interest takes place, to one... 

The Cottrell equation is derived from Pick s second law of diffusion (Section 1.5) and predicts the variation of the current in time, when a potential step is applied under conditions of large overpotential. For this equation to be valid the current must be limited by diffusion of the analyte to the electrode surface, and thus the solution has to be unstirred. The overpotential at which the reaction is driven must be large enough to ensure the rapid depletion of the electroactive species (O) at the electrode surface, such that the process would be controlled by the diffusion to the electrode. This equation is most often applied to potential step methods (e.g., chronoamperometry see Chapter 11) ... 

Potential-step method is an electrochemical technique in which the potential of the working electrode is either held at constant or stepped to a predetermined value, and the resulting current due to Faradaic processes and double-layer charging processes occurring at the electrode (caused by the potential step) is monitored as a function of time. Especially for practical electrochemical sensor in real-world application, chronoamperometry is preferred due to its simplicity and low cost of instrumentation. Besides its wide use in most electrochemical sensor systems, chronoamperometry has been used in the understanding of the kinetics of the electrochemical processes as well. 

FIG. 2 Principal methods for inducing and monitoring interfacial processes with SECM (a) feedback mode, (b) induced transfer, and (c) double potential step chronoamperometry. 

The motivation behind the considerable effort that was exerted in the development of DCV [42, 49, 50, 69] was based on the need to make CV and LSV quantitative tools for the study of electrode kinetics. At that time, there were three major problems that had to be overcome. These were (a) the precision in the measurement of Ep and AEp, (b) the problem with accurately defining the baseline for the reverse sweep and (c) the problem as to how to handle Rn in a practical manner. The development of DCV did indeed provide suitable solutions to all three of these problems, although the methods developed to handle the Ru problem [41, 42] only involve the derivative of the response in terms of precision necessary for the measurements. More recent work [55, 57] is indicative that the precision in Ep/2, Ep) and AEP measurements can be as high as that observed during DCV (see Sect. 3.4). Also, a recent study in which rate constants were evaluated using CV, DCV, and double potential step chronoamperometry for a particular electrode reaction showed that the precision to be expected frcm the three techniques are comparable when the CV baseline, after subtracting out the charging... 

Double-potential-step chronoamperometry does not require precise control of potential. It is only necessary that the potential during each step be at a value for which the desired reaction occurs at the mass-transport-limited rate. Thus, it was not necessary to correct for solution iR drop in these experiments as it would have been if cyclic voltammetry had been selected as the method for quantitative evaluation of the rate constant. 

We describe here that the redox oligomer wires fabricated with the stepwise coordination method show characteristic electron transport behavior distinct from conventional redox polymers. Redox polymers are representative electron-conducting substances in which redox species are connected to form a polymer wire.21-25 The electron transport was treated according to the concept of redox conduction, based on the dilfusional motion of collective electron transfer pathways, composed of electron hopping terms and/or physical diffusion.17,18,26-30 In the characterization of redox conduction, the Cottrell equation can be applied to the initial current—time curve after the potential step in potential step chronoamperometry (PSCA), which causes the redox reaction of the redox polymer film ... 

Kakutani et al. described an ion-transfer voltammetry and potentiometry method for the determination of acetylcholine with the interface between polymer-nitrobenzene gel and water [13]. The PVC-nitrobenzene gel electrode was prepared as described by Osakai et al. [14]. The transfer of acetylcholine ions across the interface between the gel electrode and water was studied by cyclic voltammetry, potential-step chronoamperometry, and potentiometry. The interface between the two immiscible electrolyte solutions acted as the ion-selective electrode surface for the determination of acetylcholine ions. 

For decades the electrochemical techniques, i.e., potential, current, or charge step methods such as - chronoamperometry, - chronocoulometry, - chrono-potentiometry, coulostatic techniques were consid-... 

Chronopotentiometry closely resembles chronoamperometry with the exception that the role of current and potential are reversed. In chronopotentiometry the current is controlled and is the variable and the electrode potential is the observable. A single step of the current or a double step can be employed. The double step method called current reversal chronopotentiometry is more information-rich as in previous comparisons. Both the applied currenttime wave form and the potential-time response for a reversible electrode process are illustrated in Fig. 4. The current step from 0 to a predetermined value depending upon the experimental conditions is maintained until time... 

Double potential-step chronoamperometry offers two attractive features, at least. First, since the method includes potential steps to E values at which the heterogeneous... 

In many preparative applications of EGBs the rate-determining step in product formation is the proton transfer. This is often the case when the deprotonated substrate is removed in a fast product-forming reaction (cf. Sec. II.B). For EGBs formed in situ, electrochemical methods such as cyclic voltammetry (CV), derivative cyclic voltammetry (DCV), linear sweep voltammetry (LSV), double-potential-step chronoamperometry (DPSC), and other electroanalytical methods can often be used to estimate the kinetics of proton transfer from the substrate to the EGB. When the EGBs are formed ex situ (because the acidic... 

This experiment, called double potential step chronoamperometry, is our first example of a reversal technique. Such methods comprise a large class of approaches, all featuring an initial generation of an electrolytic product, then a reversal of electrolysis so that the first product is examined electrolytically in a direct fashion. Reversal methods make up a powerful arsenal for studies of complex electrode reactions, and we will have much to say about them. 

Studies of tethered electroactive species are less sensitive to pinholes than experiments with solution reactants and blocking layers, although heterogeneity and roughness of the substrate and film defects can still play a role. The rate constant, k, in this case has units of a first-order reaction (s ). Rate constants can be determined by a voltammetric method as described earlier for electroactive monolayers (Section 14.3.3). In addition potential-step chronoamperometry can be employed, in which case the current follows a simple exponential decay (88, 90, 91) ... 

Cydodextrins (CyDs) with their largely hydrophobic cavities of variable size and numerous ways of chemical modification are the subject of intensive electrochemical research induding both their behavior in homogeneous solutions and in thin films attached to the electrode surfaces [1-8]. Electroanalytical methods measuring the current response to the potential applied, linear scan, staircase, and pulse voltammetries, and potential-step techniques such as chronoamperometry and... 

If the relation (2.50) is maintained, then a relatively simple equation for calculation of the equilibrium constants can be derived for the method of chronoamperometry, where the current-time response is analysed after the potential step is applied. 

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