Oxygen polarization potential

A unique application of the solid oxygen electrolytes is in dre preparation of mixed oxides from metal vapour deposits. For example, the ceramic superconductors described below, have been prepared from mixtures of the metal vapours in the appropriate proporhons which are deposited on the surface of a solid electrolyte. Oxygen is pumped tluough the electrolyte by the application of a polarizing potential across the electrolyte to provide the oxidant for the metallic layer which is formed. 

In alkaline solution, silver is a second option, but silver must be protected against anodic oxidation and partial dissolution by safely polarizing it to at least -200 mV vs reversible oxygen electrode potential. 

In addition, the concentration of potential micelle-formers will decrease with depth of burial of the source rock (as the generation of nitrogen, sulfur and oxygen polar compounds, which are more likely to form micellar solution, decreases with increasing depth). 

The rate of diffusion of oxygen to the cathode is proportional to the partial pressure of the oxygen in the sample to which the electrode is exposed, and the amperometric current is proportional to this. Measurements are read at atmospheric pressure. Halogens and other gases (e.g., SO2) that are also reduced at the fixed polarization potential interfere. Hydrogen sulfide poisons the electrode. 

While the previous examples were limited in the anodic polarization potential either by transpassive dissolution or by oxygen evolution valve metals can be polarized to potentials of up to 100 V and above. Examples are aluminum, titanium, tantalum, hafnium, and zirconium. Formation characterization and properties of these oxides were treated in Chapter 9. 

The oxygen reversible potential of 1.23 V was confirmed indirectly by extrapolation of anodic and cathodic polarization curves on various noble metal electrodes. The interception of the polarization curves at the potential close to 1.23 V was observed with highly oxidized Pt electrode [1,8]. These results were unusual as the extrapolations were made from high cathodic and high anodic overpotentials where the surface ccmditions were different and it was expected that the mechanisms for reduction and oxidation of oxygen might be different. 

The notations from the table Hpeak - p ak current density for anodic polarization e- peak -peak potential for anodic polarization i peak - peak current density for cathodic polarization E peak - peak potential for cathodic polarization 02 - oxygen generation potential e pas -passivation potential ipas-passivation current. 

In this section, the variables related to oxygen and methanol are equipped with the subscripts ox and mt, respectively. Here, iox, imt are the ORR and MOR volumetric exchange current densities, Cox, cj are the local and reference (inlet) oxygen concentrations, Cmt, c t are the local and reference methanol concentrations, r]mt are the ORR and MOR polarization potentials (overpotentials), box, bmi are the ORR and MOR Tafel slopes, and Dox, Dmt are the oxygen and methanol diffusion coefficients, respectively. 

Figure 11. C 1j XPS spectrum from a PAN-based carbon fiber after potcn-tiostatic polarization at different potentials (vs. SCE) for 20 min in 2.7 M nitric acid solution. The spectra have been fitted with five peaks. Four peaks (G/L mix = 0.5) are separated from the principal fiber carbon peak (at 284.6 eV with G/L mix = 0.8) by 2.0 eV (carbon attached to bridged" oxygen), 3.2 eV (-C=0 carbon), 4.2 eV (-CO2H/R) and 6.1 eV (carbonate/tt- it shakeup processes). The FWHM of the peaks arising from oxidation were at about 2 eV (for polarization potentials 0.5 to 2.0 V) and 1.4 eV (for polarization potentials 2.5 and 3.0 V) (e) and (0- A nonlinear background has been included in the fit. Results of the curve fitting are shown in Table 2. (From Ref. 43.)...

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