Half-Wave Potentials shifts

In both cases, the half-wave potential shifts by RT/ ziF)vaN per pH unit, and a typical example of such a behavior is given in Fig. 9 for the transfer of two acidic fi-diketones at the water-nitrobenzene interface. These results were unexpected, since a current wave is measured at a pH where the compound of interest is by a very large majority neutral, but they in fact represent the typical behavior of ionizable compounds at the ITIES and prove that the interfacial potential and the transfer of protons plays a key role for the distribution in biphasic systems. 

Notwithstanding all previous precautions taken, some difficulties may still remain. For instance, in the reductive polarography of monovalent metal ions the half-wave potentials should differ preferably by at least 0.30 V (see p. 120) in view of the net wave separation. Simply in order to detect the presence of a second metal a difference of at least 0.1 V is required, but interferences soon arise at low concentration although derivative polarography yields some improvement, these can best be overcome by complexation of one of the metals, so that its half-wave potential shifts to the more negative side. If we take the complexation of a metal Mn+ as an example, e.g. with X6- as the complexing ion, then... 

The variation of the half-wave potentials with Jx = f(k I k2)l for CE (see Eq. (3.221b)) and EC (see Eq. (3.201c)) mechanisms is plotted in Fig. 3.27. From this figure, it can be seen that the half-wave potential shifts toward more anodic (EC) or cathodic (CE) potentials when x increases, respectively, whereas the halfwave potentials of catalytic and E mechanisms are independent of x-... 

From Eqs. (3.287) and (3.290), it can be inferred that, when total equilibrium conditions are considered for the precedent and subsequent chemical reactions to the charge transfer reaction, the shape and height of the voltammetric curve are not affected although the half-wave potential shifts toward more cathodic or anodic... 

Credi, Raymo and coworkers reported in 2002, the preparation of a new type of carbohydrate-coated, dendronized ferrocenes [46], The structures of these den-drimers are illustrated by compounds 14 and 15. Binding interactions with p-CD were investigated by liquid secondary ion mass spectrometry, 11 NMR spectroscopy, voltammetry and circular dichroism. Upon addition of P-CD, cyclic voltammetric experiments showed data similar to those obtained with our dendronized ferrocenes, that is, a CD-induced current level decrease and anodic half-wave potential shift. At 22°C, these authors obtained K values of 2,000 200 and 1,300 200 M-1 for the complexation of 14 and 15, respectively, by p-CD in 0.1MNaClO4. Similar dendrimers in which carbohydrate branches are covalently attached to both cyclopentadienyl rings of the ferrocene residue were not bound at all by P-CD, reflecting the shielding of the core ferrocene center in these more symmetric compounds. 

In the boundary between cases I and V, which corresponds to E1/2 = E°, and the half-wave potential shifts with the substrate concentration... 

Polarograms and cyclic voltammograms for tris(bipy) complexes of Cr and Cr in DMF have been reported. On the basis of the half-wave potential shift caused by methyl substitution on the bipy ligands it was concluded that each excess electron of the reductant species of the redox systems Cr(bipy)3/Cr(bipy)3 Cr(bipy)3 /Cr(bipy)3 and Cr(bipy) /Cr(bipy)3 " occupies a ligand n orHtal. The electrochemical reduction of [CrPh2(bipy)2]I at Pt and Au electrodes in MeCN and Me2SO has been investigated. Two reversible one-electron reductions were observed, as in reaction... 

From the half-wave potential shift with the logarithm of only the sum of the rate constants can be evaluated in the case of EC mechanism. 

As the concentration of the electrolyte decreases, the limiting current is unaltered but, in contrast, the half wave potential shifts to more negative potentials, as shown in figure lb). When the electrolyte concentration is zero this shift is about 200 mV, a much higher value than that predicted by Oldham (6). This is probably an indication of slow kinetics when the electrolyte concentration decreases as a result of double layer effects. 

The stability for ORR of the 16.1% Rh catalyst was investigated under the same conditions as the sulfided Rh catalysts prepared by DP followed by H2S treatment. The 16.1% Rh catalyst showed a smaller half wave potential shift (0.012 V) than the Rh-900 sample (0.019 V) after a stability test for 24 h (Fig. 4) while with a more positive onset potential than the Rh-900. The results indicate that the grafted sample is more stable than the Rh-900 (rtem = 8.7 nm, rxrd = 8.0 nm) even with a much smaller particle size (rtem = 7nm, rxrd 3 mn). Hence, we can conclude that grafting enhances the stability of the Rh catalysts. 

---