Pulse potentiostatic method

Various types of controlled-potential pulsing are shown in Fig. 5.18. The simplest case is the single-pulse potentiostatic method (Fig. 5.18A). The current-time (I-t) curves obtained by this method have already been described in Section 5.4.1, Eq. (5.4.10) and (5.4.14). 

The double-pulse potentiostatic method (Fig. 5.18C) is suitable for studying the products or intermediates in electrode reactions, formed in the A pulse by means of the B pulse. For example, if an electroactive substance is reduced in pulse A and if pulse B is sufficiently more positive than pulse A, then the product can be reoxidized. The shape of the I-t curve in pulse B can indicate, for example, the degree to which the unstable product of the electrode reaction is changed in a subsequent chemical reaction. 

The simplest case occurs when a number of nuclei is formed at the beginning of the process and does not change with time instantaneous nucleation). This is the case when the electrolysis is carried out by the double-pulse potentiostatic method (Fig. 5.18B), where the crystallization nuclei are formed in the first high, short pulse and the electrode reaction then occurs only at these nuclei during the second, lower pulse. A second situation in which instantaneous nucleation can occur is when the nuclei occupy all the active sites on the electrode at the beginning of the electrolysis. 

The mechanism of anodic dissolution of silver in cyanide solutions has been studied by Bek and coworkers [378-380]. For example, using [379] the rotating disc electrode and pulse potentiostatic method, it has been found that the limiting step involved the formation, at the electrode surface, of the adsorbed complex with two... 

UPD process is significantly enhanced by introducing lead into Se [322]. Pb UPD has also been studied on palladium [323], from the point of view of catalytic applications and on tellurium using electrochemical impedance spectroscopy [324]. The latter process has been found irreversible owing to the Pb-Te bonds formation. Periodic multilayer structures in Pb-Se-Te system have been studied using pulse potentiostatic methods [325]. 

Potentiostatic Methods. A potentiostatic method has been used to synthesize PANI-NFs deposited on stainless steel electrodes [263-265] and in an acidic aqueous solution containing methanol [266]. High-quality nanofibrous PANI film was synthesized on Ti electrodes from an aqueous solution of aniline and HNO3 by a pulse potentiostatic method [267]. PANI-NFs were also prepared by a template-free constant potential method on a stainless steel electrode [268]. Both the hydrophilicity and the lipophilicity of the modified stainless steel smface were enhanced by the nanostructured PANI, and a super-amphiphilic surface was obtained in this way. 

Y. Hu, T. Yang, X. Wang, and K. Jiao, Highly sensitive indicator-free impedance sensing of DNA hybridization based on poly (m-aminobenzenosulfonic acidJ/Ti02 nanosheetmembranes with pulse potentiostatic method preparation, CheriL Eur. J. 16,1992-1999 (2010]. 

Alexey Scheludko started his scientific experimental and theoretical studies in the field of electrochemical phase formation and published six scientific papers on this subject in the period (1950-1956) [48-53]. Four of them [48, 50, 52, 53] were devoted to the nucleation kinetics and, in my opinion, a most significant achievement described in these articles was the development of the pulse potentiostatic method. 

Fig. 5.18 Potentiostatic methods (A) single-pulse method, (B), (C) double-pulse methods (B for an electrocrystallization study and C for the study of products of electrolysis during the first pulse), (D) potential-sweep voltammetry, (E) triangular pulse voltammetry, (F) a series of pulses for electrode preparation, (G) cyclic voltammetry (the last pulse is recorded), (H) d.c. polarography (the electrode potential during the drop-time is considered constant this fact is expressed by the step function of time—actually the potential increases continuously), (I) a.c. polarography and (J) pulse polarography...

Sn(II) and Nb(V) species changed their coordinations with the liquid composition. Nb-Sn alloy samples were prepared by the potentiostatic method and analyzed. The results showed that the Nb content in the alloy could be increased by increasing the bath temperature to 160 °C and increasing the NbCh content in the bath. However, increasing the NbCls mole fraction in the bath also increased the viscosity of the bath. Pulse electrolysis was found to be effective in increasing the Nb content in the alloy. The maximum Nb content in the alloy was 60.8 wt% from constant potential electrolysis and 69.1 wt% from pulse electrolysis. XRD diffraction patterns showed that the electrodeposits contained crystalline Sn and NbsSn which is a superconductor material. 

As explained earlier, in transient electrochemical methods an electrical perturbation (potential, current, charge, and so on) is imposed at the working electrode during a time period 0 (usually less than 10 s) short enough for the diffusion layer 8 (2D0) to be smaller than the convection layer (S onv imposed by natural convection. Thus the electrochemical response of the system investigated depends on the exact perturbation as well as on the elapsed time. This duality is apparent when one considers a double-pulse potentiostatic perturbation applied to the electrode as in the double-step chronoampero-metric method. 

Redox potentials for copper systems have been based on a variety of approaches including (i) redox titrations, (ii) potentiostatic methods involving spectral monitoring, (iii) cyclic voltammetry (CV), and (iv) pulsed methods. Of these, CV measurements are by far the most prevalent. No effort has been made in this treatise to identify the method used for a specific reported potential value unless the method itself appeared to be pertinent. 

For the study of diffusion phenomena in solids it is also possible to work with potential pulses (potentiostatic pulses) or with constant current pulses (galvanostatic pulses). Examples described in the following paragraphs are based on the coulometric titration method described in Chapter 3. Weppner and Huggins reviewed these methods.In a continuous series of pulses the concentration of lithium in a sheet of aluminum is increased. The diffusion in each pulse is followed by either potential or current measurements. 

Each of these two procedures can be varied by proceeding from a low to a high current density (or potential) or from a high to a low current density (or potential) the former is referred to as forward polarisation and the latter as reverse polarisation. Furthermore, there are a number of variations of the potentiostatic technique, and in the potentiokinetic method the pwtential of the electrode is made to vary continuously at a predetermined rate, the current being monitored on a recorder in the pulse method the electrode is given a pulse of potential and the current transient is determined by means of an oscilloscope. 

The electrical double-layer structure of a Pt/DMSO interface has been investigated using the potentiostatic pulse method.805 The value of C at E = const, as well as the potential of the diffuse layer minimum, have been found to depend on time, and this has been explained by the chemisorption of DMSO dipoles on the Pt surface, whose strength depends on time. Eg=Q has been found11 at E = -0.64 V (SCE in H2O). 

In this method, which was proposed in 1957 by Geoffrey C. Barker, a series of potentiostatic pulses of increasing amplitude (Fig. 23.6a) are applied to the electrode. Between pulses the electrode is at a potential where there is no reaction during... 

The method of potentiostatic pulses is sometimes combined with the DME (called pulse polarography). hi this case the pulse frequency should match the drop frequency, where each pulse is used at a definite time in the drop life, hi Barker s method, large pulse amphrndes are used. Other versions of the potentiostatic pulse technique are square-wave and staircase voltammetry here smaU-amphtude pulses are used. 

It is reasonable to ask at this point Are there other approaches to reach stability with grace in true potentiostatic circuits The answer is indeed affirmative, but unfortunately with qualifications. One technique is discontinuous control of cell potential. It is not a new approach it was, in fact, the method used in the very first electronic potentiostat by Hickling in 1942. The principle is quite simple Current pulses are applied to the counterelectrode so that the desired potential is maintained between reference and working electrode. Since the potential can be measured between pulses, there is no iR drop. Cell potential is not steady it depends on the sensitivity of the comparator circuit and the rate at which current demand can be met. 

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