Depolarizers adsorption

The positive S.P. of up to 3 v. which is obtained for the adsorption of alkali metals on a W surface provides evidence for positive ion formation with electrons transferred from the adsorbate to the metal. For Na and Cs there is reasonable agreement between the values of the experimental dipole moment (M = 10 A( /47r300o-me, as considered in Sec. III,C) measured at low coverage, where the effects of mutual depolarization may be neglected, and the calculated values based on the electronic charge (e = 4.80 X e.s.u.) and the radius of the positive ion do (105) ... 

Eugenol, like other phenolic compounds, is a structurally non-specific drug. The pharmacological action is not directly subordinated to chemical structure, except to the extent that structure affects physicochemical properties, as adsorption, solubility, pKa, and oxidation-reduction potential, factors which influence permeability, depolarization of the membrane and protein coagulation [34],... 

Sometimes the polarographic behavior of heteroaromatic compounds is complicated by adsorption of depolarizer and/or products the adsorbability generally increases with the number of aromatic nuclei in the molecule. In the reduction of benzoyl pyiidines270 it was found that the adsorption of both depolarizer and products was important in acid solution, whereas only the former was adsorbed at high pH. 

In a similar fashion, adsorption of atoms or molecules onto a surface can raise or lower the value of the work function. Figures 16 and 17 illustrate the affect of CO and Na adsorption on the work function of Rh(l 11). For the case of carbon monoxide, the presence of the double layer at the surface leads to the polarization of CO with the negative end of the induced dipole oriented away from the surface. The presence of this dipole reinforces the dipole potential and conseqnently increases the work function. For the case of sodinm, charge transfer occurs upon adsorption leaving an electropositive element at the surface. This in turn decreases the effective magnitude of the dipole potential and lowers the work fhnction. The data of Figure 17 also illustrate the role of adsorbate-adsorbate interactions as depolarization of the sodinm occurs at near-monolayer coverage and reduces the effect. The adsorption of gas molecules on insulator... 

Figure 17 The work function of a Rh(l 11) surface is initially lowered by the adsorption of sodium atoms. The small increase at higher coverages arises from the depolarization of the sodium overlayer...

In conventional additive-based electroplating, competitive adsorption for surface sites occurs coincident with substrate immersion and the onset of metal deposition. Additive adsorbate coverage evolves with metal deposition and is often accompanied, to some extent, by incorporation into the growing solid with associated influence on the microstructure and resulting physical properties. The adsorbates can have an accelerating or inhibitory effect on the metal deposition process. Inhibition manifests as an increase in electrode polarization with additive concentration while accelerating or depolarizing additives exhibit the opposite trend. Recent use of... 

However, the presence of extraneous ions such as Fe or Cl, eitha-in clays or soils, may not be acceptable for environmental reasons, not to mention their probable adsorption by clays. The idea of a depolarization reaction leaves open, however, the possibility of a suitable reaction (other than O2 evolution) at the anode, for example, some organic oxidation such as that of HCOO or CH3COO or CH 3OH or CeHs OH. This may also provide a method of using anodic oxidation to clean soils contaminated by organics. 

The electrochemical oxidation of methanol has been extensively studied on pc platinum [33,34] and platinum single crystal surfaces [35,36] in acid media at room temperature. Methanol electrooxidation occurs either as a direct six-electron pathway to carbon dioxide or by several adsorption steps, some of them leading to poisoning species prior to the formation of carbon dioxide as the final product. The most convincing evidence of carbon monoxide as a catalytic poison arises from in situ IR fast Fourier spectroscopy. An understanding of methanol adsorption and oxidation processes on modified platinum electrodes can lead to a deeper insight into the relation between the surface structure and reactivity in electrocatalysis. It is well known that the main impediment in the operation of a methanol fuel cell is the fast depolarization of the anode in the presence of traces of adsorbed carbon monoxide. 

One of the most attractive applications of bimetallic surfaces is for the analysis of their performance on the adsorption and oxidation reactions of interest in fuel cells. It is well known that one of the main limitations during the operation of a methanol fuel cell is the fast depolarization of the anode in the presence of traces of the adsorbed carbon monoxide. 

Martus and Becker76 utilize the oxygen-adsorptive power of activated carbon to depolarize the cathode of an alkaline primary... 

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