Polishing electrode

Later, polished and unpolished pc-Pb electrodes were studied600 and the Parsons-Zobel plots at c > 0.005 M NaF were found to be linear, with the value of/re = 1.15 for the polished electrode. At c 0.005 M NaF, nonlinear Parsons-Zobel plots, which are characteristic of solid pc electrodes, were observed. The Ch a curves, calculated for polished pc-Pb taking into account the roughness of the surface (Cf ° = 0.26 F m-2, cr = 0.18 F m 2), were compared with those obtained on the basis of the GCSG theory for liquid Hg. C, E curves were obtained for NaF + H20 solutions with the addition of various amounts of thiourea (TU). The... 

The pzc of a pc-Cd renewed by cutting was determined in dilute fluoride and sulfate solutions by capacitance measurements.645,646 The C, E curves exhibited distinct minima whose depth increased with increasing dilution of the solution (Table 15). This value is ca. 30 mV more negative than that for polished electrodes and reflects the more disturbed surface stmcture of a renewed electrode. Adsorption of aliphatic alcohols and acids has also been studied on these electrodes.645,646... 

Such effects are observed inter alia when a metal is electrochemically deposited on a foreign substrate (e.g. Pb on graphite), a process which requires an additional nucleation overpotential. Thus, in cyclic voltammetry metal is deposited during the reverse scan on an identical metallic surface at thermodynamically favourable potentials, i.e. at positive values relative to the nucleation overpotential. This generates the typical trace-crossing in the current-voltage curve. Hence, Pletcher et al. also view the trace-crossing as proof of the start of the nucleation process of the polymer film, especially as it appears only in experiments with freshly polished electrodes. But this is about as far as we can go with cyclic voltammetry alone. It must be complemented by other techniques the potential step methods and optical spectroscopy have proved suitable. 

After the cell was assembled, the screws on the window holder were adjusted such that the window is parallel to the working electrode. Since the polished electrode surface was inevitably rounded to some extent, it was assumed that they were most parallel when the interference fringes were observed on the center of the electrode. 

A strong argument for this assumption has been that this effect always appears in voltammetric experiments with freshly polished electrodes and only in the reverse sweep of the first cycle [6, 51,... 

Solid electrode performance can be affected by the electrode s previous history. A freshly polished electrode surface is virtually free of functional groups. To what extent its electrochemical behaviour changes in use depends very much on the electrode material and electrochemical pretreatment procedures [98]. 

The electrical conductivity was measured by W. H. Ross, who found that in all cases the conductivity of the salt soln. was increased with time, especially with the more dil. soln. This is due to the decomposition of the salts under the influence of the platinum-black of the electrodes with polished electrodes, the effect is considerably smaller. The base itself is oxidized even more rapidly than the salts. The soln. are in all cases decomposed by the platinum electrodes, and G. M. J. MacKay showed that tin does not decompose the soln. at all, while copper decomposes the soln. completely. The order in which the metals were found to decompose the soln. is tin, platinum, silver, nickel, mercury, and copper. The electrical conductivity of hydroxylamine, using tin electrodes, in terms of mercury at 18°, with v vols. of soln. per mol, is as follows ... 

The area of a polished electrode (taken to be the projected or geometric area in most voltammetric experiments at times > 1 s) usually is measured directly or electrochemically. If the electrode is of regular geometry, such as a disk, sphere, or wire of uniform diameter, its characteristic dimensions can be measured by use of a micrometer, optical comparator, or traveling microscope and the area calculated. 

The application of a typical train of pulses, when using stainless steel electrodes, resulted in small polarization of the electrodes and the appearance of a residual low DC component (<2 V). To avoid polarization, it is recommended to switch electrode polarity after each treatment and to clean and polish electrodes after each experiment. When employing stainless steel electrodes one observes, in some culture media, the formation of precipitates. It is, therefore, recommended to employ platinum electrodes, which do not lead to precipitation. 

Fig. 106. Photopotential decay transients following a ns illumination pulse on n-CdSe in contact with selenide solution. The lower curves show the mechanically polished electrodes with a damaged surface layer and the upper curves the same after etching.

One of the inherent problems associated with any heterogeneous technique such as voltammetry is the reproducibility of the properties and nature of an electrode surface. Traditionally, studies in which this was crucial utilized a hanging mercury drop, or dropping mercury electrode which ensured a continuously renewable surface. Cardwell et al. (1996) have described improved techniques for polishing electrodes which will go some way towards providing more reproducible electrode surfaces. Reproducibility may be assisted by the development of disposable electrodes (for example, Wang and Chen, 1994) that have developed disposable enzyme microelectrode array strips for glucose and lactate detection. 

Compton et al. [40] proposed the immobilization of MWCNTs on basal plane pyrolitic graphite electrodes by abrasively attaching CNTs on the electrode siuface by gently rubbing a polished electrode on a filter paper containing 2 mg MWCNTs for 1 min. 

Most of the solvents used in electrochemistry, and particularly water, present strong absorption in the mid-IR range. Therefore the use of external reflection IR spectroscopy for the in-situ observation of electrode processes requires a considerable reduction in the solution thickness in the path of the IR beam. Only a very thin layer of electrolyte between electrode and IR window is allowed in order to have enough energy reaching the electrode surface. Typically, the thickness of the solution layer produced by a well-positioned, flat-polished electrode is of the order of 1 - 5 pm. Within this cavity, which has been described by Yeager et al. as diffusionally decoupled, migration is the predominant form of mass transport [26]. 

Often analytical methodology for quality control is limited by the ease with which the method can be applied at the manufacturing site. Reproducibly manufactured, disposable, integrated electrochemical instruments would simplify calibration and eliminate the need for analysts to remove and polish electrodes. 

The literature contains descriptions of trace crossings or nucleation loops that normally appear on the reverse sweeps of the first cycle in all voltammograms, provided that the scan reversal lies close to the peak potential [44a]. This has been interpreted as the start of the nucleation process of the corresponding polymer. A strong argument for this assumption has been that this effect always appears in voltammetric experiments with freshly polished electrodes and only in the reverse sweep of the first cycle [6,44,54]. 

Rinse the polished electrode with nanopure water, and dry with N2 gas. 

The technique developed by Bewick for use with a dispersive IR spectrometer is termed electrically modulated infrared spectroscopy (EMIRS) and is essentially a direct development of the UV-VIS specular reflectance technique [50], modulated specular reflectance spectroscopy (MSRS). As in MSRS, radiation is specularly reflected form a polished electrode surface while the electrode potential is modulated with a square wave between a base potential and the working potential at which the process of interest occurs the wavelength range of interest is then slowly scanned. Only that... 

In most chronoamperometry, with measurement times of 1 ms to 10 s, the diffusion layer is several micrometers to even hundreds of micrometers thick. These distances are much larger than the scale of roughness on a reasonably polished electrode, which will have features no larger than a small fraction of a micrometer. Therefore, on the scale of the diffusion layer, the electrode appears flat the surfaces connecting equal concentrations in the diffusion layer are planes parallel to the electrode surface and the area of the diffusion field is the geometric area of the electrode. When these conditions apply, as in Figure 5.23a, the geometric area should be used in the Cottrell equation. 

In the external method, a light ray strikes the electrode surface from the solution phase. On hitting a well-polished electrode surface, the light is reflected from the interface back to the solution. A quantitative comparison is then made of the properties of the incidental and reflected light. It should be noted that the reflection causes change in the properties of the light, that is, in amplitude and phase, so that the reflected light provides information about the interface. 

A setup suitable for work with highly reflective solid electrodes (e.g. platinum, gold or glassy carbon discs) has been described by Salbeck [145]. As shown in the cross section in Fig. 5.39, the polished electrode surface is mounted close to the NIR-transparent cell bottom, leaving only a thin layer of electrolyte solution in the narrow gap. Connection to the NIR spectrometer is accomplished with a fiber optic... 

The CPE model has been used to study PC Au, Cd, Ag, Bi, Sb and it has been found that for electrochemically polished electrodes the surface roughness is very small compared with mechanically polished surfaces [5,15,16, 22, 35, 36] (see also Chap. 8 in Vol. 3). 

Sonicate the polished electrode sequentially in distilled water, ethanol, and distilled water for 5 min each to ensure complete removal of the alumina particles and other impurities. 

The silicone rubber-coated and fire-polished electrode to be used has to be filled with an ionic solution. It is very important to cleanse the material to obtain good patches. Electrodes have to be kept free from dust, and all solutions to be used have to be filtered (using a Millipore 0.2 pm filter). The compositon of the electrode solution as well as the chamber bath solution will depend on the particular experiment and on the configuration of the patch that is going to be obtained. The level of the bath solution in the recording chamber is adjusted to be as low as possible, in order to obtain small pipette capacity and, consecutively, low pipette noise. 

There are limits to the reduction of the electrode surface area. Small surface area polished electrodes demonstrate significant polarization potentials, which decrease pacing efficiency. In theory, extremely small electrodes may be designed like arrowheads therefore they may be more likely to penetrate or perforate the myocardial wall. This problem can be overcome by placing a protective soft polymer collar around the base of the electrode to prevent penetration (Fig. 1.12). Such a protective collar, however, may prevent the electrode from making contact with the endocardium. Despite these criticisms, there is no evidence after more than a decade of clinical experience, of any unique problems, associated with very small surface area electrodes. 

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