Gold electrodes polarization

According to a Macherey-Nagel application note [35], a mixture of 20 ng each of (i)-cysteine, (L)-glutathione, and (L)-penicillamine was resolved in less than 12 min by HPLC. The method used a Nucleosil 100-5SA column (15 cm x 4.6 mm i.d.) with aqueous 4.5 g/L ammonium citrate-6 g/L phosphoric acid at pH 2.2 as the mobile phase (eluted at 1 mL/min) and electrochemical detection at a gold electrode polarized at +800 mV. 

The PPy was doped with p-toluene sulfonate (tosylate) or chloride and its delamination was tested with two chloride salt solutions injected in the defect (potassium chloride or tetrabutylammonium chloride). The aim of this work was to correlate the delamination rate with reduction of the polymer, corresponding either to the release of the doping anions or to the incorporation of cations. The measurements were carried out in air or in an oxygen-free atmosphere with the gold electrode polarized at a potential whieh simulates iron eorrosion (—0.66 V vs. Ag/AgCl) (Figure 16.9). 

The gold electrode polarization curves registered in all the atmospheres are similar (Fig. 5) at high current densities (/ > 10 mA/cm, E —(0.9- 0.6) V). The slopes of the Tafel sections are equal to 160 mV in the CO2 or CO atmosphere and 240 mV in the He atmosphere. If the current is less than 10 mA/cm (Fig. 5), the influence of the gaseous atmosphere is clearly pronounced. In the CO atmosphere the polarization curves have a maximum-current platform extended along the potential axis (up to 0.8- 1.0 V). A small current jog 0.1 0.15 V long was observed. A smoothly descending polarization curve is obtained in the CO2 atmosphere. The stationary potentials (Fig. 7) are similar in CO2 or He atmosphere but differ sharply in CO. In the CO atmosphere the stationary potentials at... 

Kunimatsu K, Aramata A, Nakajima N, Kita H. 1986. Infrared spectra of carbon monoxide adsorbed on a smooth gold electrode Part II. EMIRS and polarization-modulated IRRAS study of the adsorbed CO layer in acidic and alkaline solutions. J Electroanal Chem 207 293-307. 

Within the promoter there can be subtle structural differences that influence the polar interaction with the protein. For example, Figure 5 illustrates the cyclic voltammograms of cytochrome c obtained at a gold electrode modified with isomers of pyridine-carboxylaldehyde-thiosemi-carbazone (PATS). 

A gold electrode with self-assembled monolayers, in the absence of any redox species, is an almost ideally polarized (i.e., purely capacitive) interface. A Nyquist... 

The birefringence is measured using apparatus of the type shown in Fig. 8.10(a). He-Ne laser light (/. = 0.633 /mi) is passed through the polarizer P, and then through the electroded specimen. The specimen is in the form of a polished plate, of thickness t typically 250 /mi, carrying gold electrodes with a gap of approximately 1mm. 

Voltammetry study made on platinum and gold needle-shaped electrodes have shown, that at low electrode polarization rates (< 0.1 V s"1) voltammograms exhibit two well-defined waves of carbon dioxide electroreduction with limiting currents and half-wave potentials - (A) E 1/2 = - 0,44 V (B) E m = - 0,78 V (Fig. 2). 

Suitable working electrodes for voltammetry are those that can be driven to take up a new potential in response to an applied external voltage, a process known as electrode polarization. Reduction or oxidation of an electrochemically active species at a working electrode results in depolarization of the electrode. The word depolarizer is therefore sometimes used to describe an electrochemically active species. In voltammetry, the working electrode may be fabricated from metals such as gold or platinum, various forms of carbon, or metallic mercury. 

It follows therefrom that our results can be connected with the injection of current carriers by the gold electrode at the organic dye. The degree of this injection depends on the polarity of the potential applied to the gold electrode. 

The electrode polarization could be reduced greatly by improving the electrode contacts with vacuum sputtered gold or silver powder films pressed on the pellets. Also, blocking the electrodes with thin mica sheets prevented the discharge of the cations and enabled us to recognize in our results the effects of the electrode polarization. 

Indirect bipolar (IB) polarization of the catalyst film in a ring-shaped electrochemical cell is realized by using the two gold electrodes as feeder electrodes. For advanced characterization of the cell, a third electric connection may be added. This latter, connected to the catalyst film itself, permits measurements also in the direct (monopolar) polarization mode, which is useful for the determination of the current bypass. 

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