Glassy carbon, characteristics

Cyclic voltammetry, square-wave voltammetry, and controlled potential electrolysis were used to study the electrochemical oxidation behavior of niclosamide at a glassy carbon electrode. The number of electrons transferred, the wave characteristics, the diffusion coefficient and reversibility of the reactions were investigated. Following optimization of voltammetric parameters, pH, and reproducibility, a linear calibration curve over the range 1 x 10 6 to 1 x 10 4 mol/dm3 niclosamide was achieved. The detection limit was found to be 8 x 10 7 mol/dm3. This voltammetric method was applied for the determination of niclosamide in tablets [33]. 

The rotating disc electrode is constructed from a solid material, usually glassy carbon, platinum or gold. It is rotated at constant speed to maintain the hydrodynamic characteristics of the electrode-solution interface. The counter electrode and reference electrode are both stationary. A slow linear potential sweep is applied and the current response registered. Both oxidation and reduction processes can be examined. The curve of current response versus electrode potential is equivalent to a polarographic wave. The plateau current is proportional to substrate concentration and also depends on the rotation speed, which governs the substrate mass transport coefficient. The current-voltage response for a reversible process follows Equation 1.17. For an irreversible process this follows Equation 1.18 where the mass transfer coefficient is proportional to the square root of the disc rotation speed. 

More recently, Engel and Olesik have also concluded that formic acid is a good modifier for carbon dioxide in SFC. The results they obtained on porous glassy carbon stationary phases with 1.5% (w/w) formic acid in CO2 (16) showed that formic acid was effective because of its strong H-bond donor and very weak H-bond acceptor characteristics higher concentrations of formic acid (3%), however, were found to polymerize on the porous glassy carbon surface (17). 

Bismuth-film electrodes (BiFEs), consisting of a thin bismuth-film deposited on a suitable substrate, have been shown to offer comparable performance to MFEs in ASY heavy metals determination [17]. The remarkable stripping performance of BiFE can be due to the binary and multi-component fusing alloys formation of bismuth with metals like lead and cadmium [18]. Besides the attractive characteristics of BiFE, the low toxicity of bismuth makes it an alternative material to mercury in terms of trace-metal determination. Various substrates for bismuth-film formation are reported. Bismuth film was prepared by electrodeposition onto the micro disc by applying an in situ electroplating procedure [19]. Bismuth deposition onto gold [20], carbon paste [21], or glassy carbon [22-24] electrodes have been reported to display an... 

Figure 12.11 shows the XRD patterns of a nanocrystalline Al film obtained at a constant potential of —1.7V for 2h at 100°C in the ionic liquid [Pyip] TFSA containing 1.6 M AICI3 on a glassy carbon substrate. The XRD patterns show the characteristic diffraction patterns of crystalline Al, furthermore the peaks are rather broad, indicating the small crystallite size of the electrodeposited Al. The grain size of Al was determined using Scherrer s equation to be 34 nm. For more information on the electrodeposition of nanocrystalline aluminum in the employed ionic liquid we refer to Refs. [3, 4]. 

In Section 2 we showed that the properties of amorphous carbon vary over a wide range. Graphite-like thin films are similar to thoroughly studied carbonaceous materials (glassy carbon and alike) in their electrode behavior. Redox reactions proceed in a quasi-reversible mode on these films [75], On the contrary, no oxidation or reduction current peaks were observed on diamondlike carbon electrodes in Ce3+/ 41, Fe(CN)63 4. and quinone/hydroquinone redox systems the measured current did not exceed the background current (see below, Section 6.5). We conventionally took the rather wide-gap DLC as a model material of the intercrystallite boundaries in the polycrystalline diamond. Note that the intercrystallite boundaries cannot consist of the conducting graphite-like carbon because undoped polycrystalline diamond films possess excellent dielectric characteristics. 

The characteristics of the electrooxidation of fluorosulfate anions in the electrolysis of a potassium fluorosulfate solution in fluorosulfonic acid have been investigated. The formation of oxide layers on platinum and the modification of glassy carbon with fluorosulfate groups during anodic polarization in fluorosulfonic acid are studied. The reactions of fiuoroolefin fluorosulfation are considered and a mechanism is suggested223. Trifluoromethylation of carbonyl compounds can be achieved using bromo-trifluoromethane and a sacrificial electrode in solvents such as DMF/pyridine, and DMF/TMEDA, as seen in equation 126224. 

Probably the most widely used of these is glassy carbon, which is isotropic. However, due to its hardness and fragility, electrode fabrication is difficult, which essentially limits its use to the dimensions and forms that can be acquired commercially. The manufacture of glassy carbon consists in carbonization by heating phenol/formaldehyde polymers or polyacrylonitrile between 1000°C and 3000°C under pressure. Since glassy carbon has some amorphous characteristics, as can be seen from Fig. 7.1, it is not always homogeneous. 

Methanol oxidation by Pt/C catalysts more closely mimics the operating environment in a real DMFC. The impedance spectra characteristics of methanol oxidation on Pt/C thin films coated on a glassy carbon electrode are dependent on the potential, as shown in Figures 6.63 and 6.64. Below 0.4 V, the diameter of the semicircle decreases with increasing potential. However, the impedance spectra obtained at potentials larger than 0.4 V (0.41 and 0.415 V) show a different trend, where the diameters increase with increasing potential. Further increases in the applied potential lead to the presence of impedance spectra in quadrants II and III. Additionally, an inductance loop is observed at potentials larger than 0.3 V. 

Table 3 Performance Characteristics of the Spray Impact Detector Employing Organic and Mixed OrganicAVater Mobile Phases Glassy Carbon Electrodes...

Fig. 1. Examples of anomalies in electrochemical interface characteristics in the vicinity of Tc-(a) Current vs. temperature dependence for proton discharge on YBa2(Cuo.9Pdo,i)07 (rc = 90 K) in HC104-5.5H20 [134]. (b) Shift of impedance minima under magnetic field for Ag/Ag reaction at the YBCO/RbAg4ls interface [147] magnetic field strength 0 (1), 1 T (2). (c) Cdi vs. temperature dependences for TBCCO rc = 119 K (1) and glassy carbon (2) measured in a butyronitrile-dichloroethane quasi-Uquid solution at potentials —2.5 and —3 V (vs. Ag), respectively. Supporting electrolyte is 0.1 M tributylammonium perchlorate (TBAP) [153].

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