Electrochemical potential range

In considering RTILs as an electrolyte for these applications, it is important to know the electrochemical stability of the RTILs toward a particular electrode. For this purpose the electrochemical potential range, starting from the point where no electrochemical reaction is observed, has been estimated using the electrochemical method. The electrochemical window (denoted EW) of RTILs is a term commonly used to indicate both the potential range and the potential difference it is... 

Some mixed-valence systems are sufficiently stable to be isolated, such as Prussian Blue (Fe )4[Fe"(CN)6]3 or the much studied Creutz-Taube ion (p-pz)[Ru(NH3)5]2 (1), pz=pyrazine Flowever, in many (but not al ) cases they are less robust than their homovalent congeners, often being formed at inconveniently high or low redox potentials, or existing only in a very limited electrochemical potential range as quantified by a small comproportionation constant K. ... 

The cyclic voltammograms (CV) of the bipyridine nitrosyl ruthenium complexes may reveal multiple couples resulting from redox processes centered at the metal, the nitrosyl ligand, and the bpy ligands. Two couples are evident in the CV electrochemical potential range of +1.0 to —1.0 V vs. Ag/AgCl of a 5/ira s-[Ru(bpy)2L(NO)] complexes in organic solvent or aqueous solution. The reduction peak at the more positive value is chemically reversible, whereas the second reduction peak is practically irreversible in the CV time scale such peaks correspond to the NO "° and pro-... 

Figure 14 demonstrates why both doped and undoped polythiophene are remarkably stable in air and moisture. The electrochemical potential ranges (versus SCE) for neutral through completely p-doped polypyrrole, polyacetylene, poly-3-... 

Kg. 8. Electrochemical potential range for polymerization of 1-substituted pyrroles, 3-substitut-ed thiophenes, S-substituted indoles and thia-naphthene (V vs SCCE)... 

If we assume that the indicator s color in solution changes from that of Inox to that of In ed when the ratio [Inred]/[Inox] changes from 0.1 to 10, then the end point occurs when the solution s electrochemical potential is within the range... 

The principle of electrochemical corrosion protection processes is illustrated in Figs. 2-2 and 2-5. The necessary requirement for the protection process is the existence of a potential range in which corrosion reactions either do not occur or occur only at negligibly low rates. Unfortunately, it cannot be assumed that such a range always exists in electrochemical corrosion, since potential ranges for different types of corrosion overlap and because in addition theoretical protection ranges cannot be attained due to simultaneous disrupting reactions. 

To discover the effective potential ranges for electrochemical protection, the dependence of the relevant corrosion quantities on the potential is ascertained in the laboratory. These include not only weight loss, but also the number and depth of pits, the penetration rate in selective corrosion, and service life as well as crack growth rate in mechanically stressed specimens, etc. Section 2.4 contains a summarized survey of the potential ranges for different systems and types of corrosion. Four groups can be distinguished ... 

In this section a survey is given of the critical protection potentials as well as the critical potential ranges for a possible application of electrochemical protection. The compilation is divided into four groups for both cathodic and anodic protection with and without a limitation of the protection range to more negative or more positive potentials respectively. 

The adjustment of a protection station or of a complete protection system where there is stray current interference is made much easier by potential control. Potential control can be indispensable for electrochemical protection if the protection potential range is very small (see Sections 2.4 and 21.4). This saves anode material and reduces running costs. 

In Eq. (24-67) it is assumed that is constant in the potential range Uy resistance polarization at defects in the coating. In this case, however, a change in the /f -free potential is only possible if electrochemical polarization is also occurring. Linear polarization is, however, very unlikely in the given potential range. 

Ionic liquids possess a variety of properties that make them desirable as solvents for investigation of electrochemical processes. They often have wide electrochemical potential windows, they have reasonably good electrical conductivity and solvent transport properties, they have wide liquid ranges, and they are able to solvate a wide variety of inorganic, organic, and organometallic species. The liquid ranges of ionic liquids have been discussed in Section 3.1 and their solubility and solvation in... 

A key criterion for selection of a solvent for electrochemical studies is the electrochemical stability of the solvent [12]. This is most clearly manifested by the range of voltages over which the solvent is electrochemically inert. This useful electrochemical potential window depends on the oxidative and reductive stability of the solvent. In the case of ionic liquids, the potential window depends primarily on the resistance of the cation to reduction and the resistance of the anion to oxidation. (A notable exception to this is in the acidic chloroaluminate ionic liquids, where the reduction of the heptachloroaluminate species [Al2Cl7] is the limiting cathodic process). In addition, the presence of impurities can play an important role in limiting the potential windows of ionic liquids. 

Electrochemical measurements are commonly carried out in a medium that consists of solvent containing a supporting electrolyte. The choice of the solvent is dictated primarily by the solubility of the analyte and its redox activity, and by solvent properties such as the electrical conductivity, electrochemical activity, and chemical reactivity. The solvent should not react with the analyte (or products) and should not undergo electrochemical reactions over a wide potential range. 

Figure 5.20. Left Schematic of an O2 conducting solid electrolyte cell with fixed P02 and PO2 values at the porous working (W) and reference (R ) electrodes without (top) and with (bottom) ion backspillover on the gas exposed electrodes surfaces, showing also the range of spatial constancy of the electrochemical potential, PQ2-, of O2. Right Corresponding spatial variation in the electrochemical potential of electrons, ]Ie(= Ef) UWR is fixed in both cases to the value (RT/4F)ln( P02 /pc>2 ) also shown in the relative position of the valence band, Ev, and of the bottom of the conduction band, Ec, in the solid electrolyte (SE) numerical values correspond to 8 mol% Y203-stabilized-Zr02, pc>2=10 6 bar, po2=l bar and T=673 K.32 Reproduced by permission of The Electrochemical Society.

The equilibrium (1) at the electrode surface will lie to the right, i.e. the reduction of O will occur if the electrode potential is set at a value more cathodic than E. Conversely, the oxidation of R would require the potential to be more anodic than F/ . Since the potential range in certain solvents can extend from — 3-0 V to + 3-5 V, the driving force for an oxidation or a reduction is of the order of 3 eV or 260 kJ moR and experience shows that this is sufficient for the oxidation and reduction of most organic compounds, including many which are resistant to chemical redox reagents. For example, the electrochemical oxidation of alkanes and alkenes to carbonium ions is possible in several systems... 

Electrochemical measurements on polyaniline (PANI) produce a picture of the charge storage mechanism of conducting polymers which differs fundamentally from that obtained using PTh or PPy. In the cyclic voltammetric experiment one observes at least two reversible waves in the potential range between —0.2 and -)-1.23 V vs SCE. Above -1-1.0 V the charging current tends to zero. Capacitive currents and overoxidation effects, as with PPy and PTh, do not occur The striking... 

Efficient photoelectrochemical decomposition of ZnSe electrodes has been observed in aqueous (indifferent) electrolytes of various pHs, despite the wide band gap of the semiconductor [119, 120]. On the other hand, ZnSe has been found to exhibit better dark electrochemical stability compared to the GdX compounds. Large dark potential ranges of stability (at least 3 V) were determined for I-doped ZnSe electrodes in aqueous media of pH 0, 6.3, and 14, by Gautron et al. [121], who presented also a detailed discussion of the flat band potential behavior on the basis of the Gartner model. Interestingly, a Nernstian pH dependence was found for... 

---