Cyclic voltammetry flames

The electrical double-layer structure at Au(l 11), Au(110), Au(100), and Au(210) faces and at a pc-Au electrode has been studied in 5 x 10 3 and 1 x 10-2 M LiC104 solutions in DMSO by cyclic voltammetry and impedance methods.477 The electrodes were cleaned by heating in a flame ... 

Deposition of the mixed monolayer. Deposition solutions were prepared by dissolving octadecylmercaptan [ClsSH] and the respective bipyridinium in a mixture of chloroform and methanol. The electrode was cleaned by heating it in a gas-air flame. After cooling, the electrode was immersed in the deposition solution for 15 - 30 minutes, withdrawn, and rinsed in clean methanol or chloroform. Qualitatively the most reproducible surface redox waves and lowest charging currents during cyclic voltammetry were obtained with a freshly-prepared deposition solution containing 50 mM CiaSH and 10 mM of the bipyridinium in a 1 1 volume ratio of chloroform and methanol. 

In the first study of its kind, second harmonic generation has been used to study potential induced reconstruction on Au(lll) and Au(100) by Kolb and coworkers [156]. These surfaces have been known to reconstruct in UHY when they are clean [153, 157], Surface reconstruction occurs when the surface atoms of a solid rearrange themselves in a structure different from that expected from simple termination of the bulk lattice. Various studies by cyclic voltammetry, electroreflectance spectroscopy and ex situ electron diffraction have suggested that flame-treated crystals form stable reconstructions in solution. Unfortunately, due to the lack of in situ probes, very little direct evidence for this reconstruction has been available. 

It was in 1990 that Kratschmer et al. [217,218] reported the first macroscopic preparation of in gram quantities by contact-arc vaporization of a graphite rod in a 100 Torr atmosphere of helium, followed by extraction of the resultant soot with toluene. Fullerene ions could also be detected by mass spectrometry in low-pressure hydrocarbon flames [219]. The door was opened by, Kratschmer and co-workers preparative success to extensive studies of the electrochemical behavior of the new materials. Cyclic voltammetry of molecular solutions of Ceo in aprotic electrolytes, e.g., methylene chloride/quatemary ammonium salts, revealed the reversible cathodic formation of anionic species, the radical anion, the dianion, etc. (cf. [220,221]). Finally, an uptake of six electrons in the potential range of 1-3.3 V vs. SHE in MeCN/toluene at — 10°C to form the hexavalent anion was reported by Xie et al. [222]. This was in full accordance with MO calculations. A parametric study of the electroreduction of Cgo in aprotic solvents was performed [223]. No reversible oxidation of C o was possible, not even to the radical cation. However, the stability of di- and trications with special counterions, in the Li/PEO/C 3 MoFf cell, was claimed later [224]. 

Before each measurement, single crystals were first elec-trochemically polished35 and then flame annealed for several minutes, cooled down, and either immersed into an external electrochemical cell for cyclic voltammetry (CV) characterization or mounted into an electrochemical cell of an STM. For both CV and in situ STM results, sample potentials were measured and presented vs. Ag/AgCl reference electrode. 

The Auger spectra for the carbon line can be used for checking the surface contamination that can be corroborated with the voltammograms [85]. Nevertheless, with the help of only cyclic voltammetry, we can observe and analyze easily a platinum surface that is free of the various atmospheric contaminants. Contamination is avoided because of the very short time required for the transfer of the sample from the flame treatment to the cell. This rather unusual requirement of quick transfer of the samples shows that voltammetry should be a good tool for the study of metallic surfaces in the presence of a defined and complex environment. 

The surface electrochemistry of Pt single-crystal electrodes has been exhaustively studied using cyclic voltammetry [5, 8-12, 61-67]. Phenomena of a step reconstruction and step coalescence have been observed [61]. For Pt(lll)-H20 interface, prepared by the flame annealing method, a double-layer charging has been observed only in a very narrow potential region (0.1 < E < 0.35 V (SCE) in 0.05 M H2SO4), which depends on the chemical... 

Figure 17.2 Cyclic voltammetry recorded in a flame. Aqueous solutions containing 1 X 10 mol dm (a) (NH ) H2W,20, (b) (NH4) Mo2024 and (c) NH VO were nebulized in the right-hand flame. Forward (black) and backward (red) scans at 1 V s , starting from 1 V. Reproduced with permission from Ref [17], Copyright 2012 WILEY-VCH Verlag CmbH Co. KCaA, Weinheim.

An earlier extensive study by Edmund Bowden had demonstrated the importance of using electrodes with hydrophilic surfaces in electrochemical studies of cytochrome c [46]. At that time the cyclic voltammetry of cytochrome c at gold was found to decay with time, but the response could be restored on cleaning the electrode in a soft hydrogen flame that rendered the snrface hydrophilic. It is now clear that the lack of stability was due to these samples being chromato-graphicaUy purified, lyophilized, and then stored at °C for later nse. This produced oligomeric forms of cytochrome c that fouled metal electrode surfaces. Metal surfaces are more active to adsorption of protein impnrities than tin oxide and indium oxide and more easily fouled by protein adsorption. 

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