Electrode anion structures

For instance, in situ Fourier transform infrared (FTIR) spectroscopy has been used by Faguy etal. [176] to study the potential-dependent changes in anion structure and composition at the surface of Pt(lll) electrodes in H 804 -containing solutions. From the infrared differential normalized relative reflectance data, the maximum rate of intensity changes for three infrared bands can be obtained. Two modes associated with the adsorbed anion... 

If the electrode potential is now swept sufficiently positive for the COads to disappear completely, and then reversed, a clear (V3 x V3)R30° LEED pattern is observed. By contrast, in HC104, there is little evidence of adsorbed anion structure. For methanol oxidation in sulphuric acid on Pt(lll), no structure is seen until E > 0.3 V, when LEED showed a disordered (V7 x /7)R19.10 pattern, with bands at 1249 and 1343 cm-1 associated with HSO4. At more positive potentials (>0.5 V), the 1250 cm-1 band disappears and the 1343 cm-1 band becomes very sharp, as does the V7 structure. Above 0.9 V, however, the current begins to decrease (v.s.) and the V7 structure also begins to deteriorate. There does appear to be some correlation between this structure and activity to methanol oxidation on Pt(lll) in addition, the ratio 0hso4/0co is always higher for methanol oxidation than CO oxidation. 

It is expected that the high prevalence of large pores in the polymer grown on platinum or gold enables easier passage of electrolyte into the bulk of the polymer, thus improving the rate of diffusion of ions into the sub-micron sized free volume of the polymer and improving the actuation strain rate. An earlier study by Pandey et al. [53] showed that the polymerization electrode also influenced the balance of anion/cation movement in the polymer. In this case PPy doped with naphthalene sulfonic acid (NSA) was prepared on three different electrodes. Anion movement was favoured in those films that had a more open, porous structure. The actuation was performed in aqueous NaCl electrolyte, so that the mobile cation (Na ) was smaller than the mobile anion (NSA). 

M.p. 296 C. Accepts an electron from suitable donors forming a radical anion. Used for colorimetric determination of free radical precursors, replacement of Mn02 in aluminium solid electrolytic capacitors, construction of heat-sensitive resistors and ion-specific electrodes and for inducing radical polymerizations. The charge transfer complexes it forms with certain donors behave electrically like metals with anisotropic conductivity. Like tetracyanoethylene it belongs to a class of compounds called rr-acids. tetracyclines An important group of antibiotics isolated from Streptomyces spp., having structures based on a naphthacene skeleton. Tetracycline, the parent compound, has the structure ... 

Complex ions used for electroplating are anions. The cathode tends to repel them, and their transport is entirely by diffusion. Conversely, the field near the cathode assists cation transport. Complex cyanides deserve some elaboration in view of their commercial importance. It is improbable that those used are covalent co-ordination compounds, and the covalent bond breaks too slowly to accommodate the speed of electrode reactions. The electronic structure of the cyanide ion is ... 

FIGURE 5-14 Structures of some chemical species useful for designing anion-selective electrodes (a) Mn(III) porphyrin (b) vitamin Bi2 derivative (c) tri-n-octyltin chloride (d) lipophilic polyamine macrocyclic compound. 

According to the data obtained with SXRS in salt solutions,519 520 at a < 0 the surface of Au(lll) forms a ( 3 x 22) structure as in a vacuum. At a > 0 the reconstruction disappears and the (1 x 1) structure is observed. On the reconstructed Au(l 11) surface there are 4.4% more atoms than on the (1 x 1) structure and on the reconstructed Au( 100) there are 24% more atoms than on the (1 x 1) structure.506,519 This phase transition shifts in the negative direction with the adsorbability of the anion. The adsorption-induced surface reconstruction of Au(l 11) electrodes has been studied in situ by second harmonic generation by Pettinger et al.521... 

Oxygen anions are thus now attracted to the electrode with the positive charge or the electrode which has been made positive by anodic polarization. Backspillover will continue untill the charge is neutralized. Similarly oxygen anions will be repelled from the negatively charged or cathodically polarized electrode to enter into the YSZ structure. The charges q+ and q. thus disappear and thus TV and TV vanish. 

As a rule, the melts have a strong corrosive effect, not only on the reaction products but also on the various metallic and nonmetallic structural materials used to build the cells and reactors. At high current densities, sometimes the anode effect occurs in melts during electrolysis A gas skin is formed at the electrode surface, and there is intense sparking and a drastic increase in voltage. This effect depends on the anode material and on the melt anions, but its reasons are not fully understood. An important reason is insufficient wetting of the electrode surface by the melt, which causes sticking of gas bubbles to the surface. 

Wang H, Baltruschat H. 2007. DEMS study on methanol oxidation at poly- and monocrystalline platinum electrodes The effect of anion, temperature, surface structure, Ru adatom, and potential. J Phys Chem C 111 7038-7048. 

Especially sensitive and selective potassium and some other ion-selective electrodes employ special complexing agents in their membranes, termed ionophores (discussed in detail on page 445). These substances, which often have cyclic structures, bind alkali metal ions and some other cations in complexes with widely varying stability constants. The membrane of an ion-selective electrode contains the salt of the determined cation with a hydrophobic anion (usually tetraphenylborate) and excess ionophore, so that the cation is mostly bound in the complex in the membrane. It can readily be demonstrated that the membrane potential obeys Eq. (6.3.3). In the presence of interferents, the selectivity coefficient is given approximately by the ratio of the stability constants of the complexes of the two ions with the ionophore. For the determination of potassium ions in the presence of interfering sodium ions, where the ionophore is the cyclic depsipeptide, valinomycin, the selectivity coefficient is Na+ 10"4, so that this electrode can be used to determine potassium ions in the presence of a 104-fold excess of sodium ions. 

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