Active peak current density

N) are shown relative to the individual curves in Fig. 5.14 and as the curves that would be measured in Fig. 5.15. In this case, the lower portion of the anodic polarization curve is not apparent in the net cathodic curve with the consequence that the shape of the anodic curve in this region cannot be determined under these conditions. A slight decrease in the current density of the cathodic curve near -100 mV (SHE) is due to the underlying active current density peak in the anodic metal curve. If conditions (e.g., decreased oxygen concentration) allowed these curves to become closer, the deviation would be greater, and if they touched, the net curve would become zero, and the experimental curve would be... 

It was found that polyaniline nanofibers coated with polycatechol (60-90 nm) have good electrochemical activity over a wide pH range and can catalyze the oxidation of ascorbic acid in a 0.1 M citrate buffer solution of pH 5.6 [91]. An oxidation peak of ascorbic acid appears at 0.05 V (vs. SCE). The catalytic characteristics are that its oxidation peak potential is lower than that at the bare platinum electrode and that polymer nanofibers with the diameters of 60-90 nm have a higher catalytic activity (current density) than those with diameters of 140-210 nm. 

The electrochemical catalytic activity of various Pt-porous nanoparticles for the oxidation of methanol was shown in Figure 13. The peak mass current densities recorded after 100 scan cycles were 80mAmg Pt for those porous Pt nanoparticles. The peak mass current densities were 72, 62, 58 and 51mAmg Pt for those products formed for reaction time of 3, 5, 10, and 20min at the Pt(acac)2 HDD HDA ACA DPE molar ratio of 6 36 118 12 100, respectively. As a reference point, the catalytic activity of a commercial carbon-supported Pt... 

That the number of sites, or film structure or thickness, depends on the current density is also seen if the current is increased or decreased stepwise.112 An additional activation peak of potential is needed at any increase in the current density. Conversely, upon decreasing the current density, an inverted potential peak is obtained, indicating that for some moments the current passes under previous film conditions. 

COD drop. The results do not show this pattern, but show a peak followed by a decrease in COD drop with increasing current density (Figure 4). Accordingly, microbial activity may be the major factor in the difference in COD drop obtained in tests with different current densities. 

An improvement on the SL-EPR test is the double loop, or DL-EPR, test, which is shown schematically in Fig. 39. In this test, the potential is first scanned in the anodic direction from Ecoss to a point in the middle of the passive region before the scan is reversed. The ratio of the two peak current densities, L//a, is used as the degree of sensitization indicator. During the anodic sweep, the entire surface is active and contributes to the peak current. During the reactivation sweep, only the sensitized grain boundaries contribute to the passive-active transition. Thus in unsensitized specimens there is a small / and therefore a small ratio, while in heavily sensitized specimens, /r approaches /a, as shown in... 

It will be shown later that the values of icrit, Epp, and ip, which are the important parameters defining the shape of the active-passive type of polarization curve, are important in understanding the corrosion behavior of the alloy. In particular, low values of icrit enhance the ability to place the alloy in the passive state in many environments. For this reason, the maximum that occurs in the curve at B (Fig. 5.4) is frequently referred to as the active peak current density or, in general discussion, as the active peak. It is the limit of the active dissolution current density occurring along the A region of the polarization curve. 

Polarization curves for iron, chromium, and alloys with 1, 6, 10, and 14 weight percent (wt%) chromium in iron are shown in Fig. 5.24 the environment is 1 N H2SO4 at 25 °C (Ref 21). Iron and chromium are body-centered-cubic metals, and the alloys are solid solutions having this structure. The passivation potential (Epp), the active peak current density (icrit), and the passive state current density (ip) are decreased... 

Polarization curves of Fe-18 wt% Cr alloys showing the shift in the active peak current density by 0-6 wt% Mo. Redrawn from... 

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