Carbon potential dependence

The temperature dependence of K is weU known experimentally. At a given temperature, if the composition of the gas is fixed, then equiUbrium carbon content is fixed. This composition is sometimes referred to as the carbon potential. 

Protection potentials are usually determined experimentally because of the possibilities of error. Figure 2-9 shows experimental results for the potential dependence of weight loss rates for carbon steel [29,30]. Four curves are plotted at 25°C for the following media ... 

Most sulphones are known to react with chemical reducing reagents like dissolved metals or amalgams. However, electron transfers may be produced also directly from metallic or conducting carbon cathodes maintained at a certain potential depending on the desired reducing power. We will discuss the reactivity of sulphones towards electrons issued from cathodes, especially in the light of recent results. 

Figure 37. Potential dependence of (a) amplitudes and (b) lifetimes of laser-induced PMC transients (532 run) of silicon in contact with propylene carbonate containing 0.1 M TBAP and ImM ferrocene (flatband at -0.5 V).

PEMFC)/direct methanol fuel cell (DMFC) cathode limit the available sites for reduction of molecular oxygen. Alternatively, at the anode of a PEMFC or DMFC, the oxidation of water is necessary to produce hydroxyl or oxygen species that participate in oxidation of strongly bound carbon monoxide species. Taylor and co-workers [Taylor et ah, 2007b] have recently reported on a systematic study that examined the potential dependence of water redox reactions over a series of different metal electrode surfaces. For comparison purposes, we will start with a brief discussion of electronic structure studies of water activity with consideration of UHV model systems. 

Potential Dependence of Elementary Chemical Reactions in Electrocatalysis Coupling of Carbon Monoxide and Hydroxyl Species... 

Anderson AB, Neshev NM. 2002. Mechanism for the electro-oxidation of carbon monoxide on platinum, including electrode potential dependence—Theoretical determination. J Electrochem Soc 149 E383-E388. 

Fig. 6 Representative examples of the steps involved in the convolution analysis approach to obtaining the potential dependence of the heterogeneous rate constant. From top to bottom (a) background-subtracted cyclic voltammograms as a function of scan rate (left to right 0.5, 1, 2, 5, lOVs " ) (b) corresponding convolution curves (c) corresponding potential dependence of logkhet obtained using equation (25). Figures shown are for the reduction of (MeS)2 in DMF/0.1 M TBAP at a glassy carbon electrode.

The voltammetric reduction of a series of dialkyl and arylalkyl disulfides has recently been studied in detail, in DMF/0.1 M TBAP at the glassy carbon electrode The ET kinetics was analyzed after addition of 1 equivalent of acetic acid to avoid father-son reactions, such as self-protonation or nucleophilic attack on the starting disulfide by the most reactive RS anion. Father-son reactions have the consequence of lowering the electron consumption from the expected two-electron stoichiometry. Addition of a suitable acid results in the protonation of active nucleophiles or bases. The peak potentials for the irreversible voltammetric reduction of disulfides are strongly dependent on the nature of the groups bonded to the sulfur atoms. Table 11 summarizes some relevant electrochemical data. These results indicate that the initial ET controls the electrode kinetics. In addition, the decrease of the normalized peak current and the corresponding increase of the peak width when v increases, point to a potential dependence of a, as discussed thoroughly in Section 2. 

The potential window of an electrolytic solution is determined by the reduction and oxidation of the supporting electrolyte as well as by those of the solvent. Because all these potentials depend on the indicator electrode used, the following discussion on the relation between the potential window and the supporting electrolyte is dealt with for each of the mercury, platinum, and carbon electrodes. 

The application of surface-enhanced Raman spectroscopy (SERS) for monitoring redox and other processes at metal-solution interfaces is illustrated by means of some recent results obtained in our laboratory. The detection of adsorbed species present at outer- as well as inner-sphere reaction sites is noted. The influence of surface interaction effects on the SER spectra of adsorbed redox couples is discussed with a view towards utilizing the frequency-potential dependence of oxidation-state sensitive vibrational modes as a criterion of reactant-surface electronic coupling effects. Illustrative data are presented for Ru(NH3)63+/2+ adsorbed electrostatically to chloride-coated silver, and Fe(CN)63 /" bound to gold electrodes the latter couple appears to be valence delocalized under some conditions. The use of coupled SERS-rotating disk voltammetry measurements to examine the kinetics and mechanisms of irreversible and multistep electrochemical reactions is also discussed. Examples given are the outer- and inner-sphere one-electron reductions of Co(III) and Cr(III) complexes at silver, and the oxidation of carbon monoxide and iodide at gold electrodes. 

The products and stereochemistry of the electroreduction of 1-bromo-l-phenylethane (24) and ( )-l-deuterio-1-bromo-l-phenylethane (24-d) have been investigated using DMF at mercury and glassy carbon electrodes (equation 23)50. The products, obtained in nearly quantitative yield, were strongly potential dependent as shown in Table 2. 

We believe that three factors contributed to the success these symposia have achieved. The first factor is the growing recognition that the high-carbon bottom-of-the-barrel residues offer enormous potential for higher added-value carbon products. The second factor is the general appreciation that success in the development of carbon products depends on improved understanding of carbonization chemistry. These views are certainly well justified by the development of such products as high-modulus carbon fibers spun from refined petroleum (or coal-tar) pitches. 

Fig. 59. Potential dependence of the band center frequency for adsorbed carbon monoxide on a piatinum electrode. (After [111]). Reprinted by permission of Elsevier Science.

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