Tafel plots for oxygen reduction

Figure 4. Ohmic Corrected Tafel Plots for Oxygen Reduction on Pt and Pt Alloy Electrocatalysts Prepared at Northeastern (note that PtCr/C is a system being considered only for ORR fundamentals it will not be under consideration for down-selection)...

Figure 2.17. Tafel plots for oxygen reduction reaction at a Pt working electrode [8]. (Reprinted from Journal of Electroanalytical Chemistry, 574(2), Wakabayashi Noriaki, Takeichi Masajoiki, Itagaki Masayuki, Uchida Hiroyuki and Watanabe Masahiro, Temperature-dependence of oxygen reduction activity at a platinum electrode in an acidic electrolyte solution investigated with a channel flow double electrode, 339-46, 2005, with permission from Elsevier.)...

Fig. 11 Tafel plots for oxygen reduction on FeTMPP-Cl/BP heat treated at 800 C in 0.1 M NaOH or 0.1 M H2SO4 solution with or without methanol. Temperature 25°C, Scan rate 10 mV s". Rotational speed 1000 rpm.

Figure 4.23 Experimental Tafel plot of cell voltage versus current, corrected for fuel cell ohmic and other losses, so that only cathode polarization losses are remaining. The results are normalized to platinum loading. Results with open circles are with humidified oxygen, and closed circles are with humidified air. The dashed line represents the Tafel slope behavior. Note that for all loadings the Tafel slope for oxygen reduction on platinum is the same but deviates from this behavior under mass-limiting behavior. Also note that the vertical axis is ohmic corrected fuel cell voltage, not electrode overpotential, so the voltage falls with increasing current density. (Reproduced with permission from [9].)...

The use of Tafel plots for the analysis of metal corrosion systems indicates how dissolved O2 in solution and the subsequent O2 reduction (which is under kinetic control) accelerates metal corrosion. Due to the high value of E for O2 reduction (+1.23 V vs. SHE), the intersection of the oxygen reduction and metal dissolution Tafel lines occurs at high values of E and When the reduction of both H+ and O2 drives metal corrosion (with the reduction reactions under kinetic control), one simply adds together the current-voltage Tafel lines for the two reduction reactions. A new line is then drawn for the sum of the cathodic currents on the corroding metal. The intersection of this new line with the metal oxidation Tafel line gives E and... 

Figure 3.24. Tafel plots for the oxygen reduction at various iron-based catalysts, as obtained from RDE measurements. All catalysts were heat treated in Ar at 900°C (according to Figure 2 in ref. [107] reproduced with permission of Elsevier).

Figure 2.18. Tafel plots for ORR in 0.5 M H2SO4 on different catalysts bjcdi Tafel slope at low current density bhcd Tafel slope at high current density [47]. (With kind permission from Springer Science+Business Media Journal of Applied Electrochemistry, Electrocatalytic hehaviour for oxygen reduction reaction of small nanostructured erystaUme himetaUic Pt-M supported catalysts, 36, 2006, 1143-1149, A. Stassi, Figure 9, Springer.)...

Figure 28. Svensson s macrohomogeneous model for the i— 1/characteristics of a porous mixed-conducting electrode, (a) The reduction mechanism assuming that both surface and bulk diffusion are active and that direct exchange of oxygen vacancies between the mixed conductor and the electrolyte may occur, (b) Tafel plot of the predicted steady-state i— V characteristics as a function of the bulk oxygen vacancy diffusion coefficient. (Reprinted with permission from ref 186. Copyright 1998 Electrochemical Society, Inc.)...

In alkaline solutions, electrochemistry of oxygen is not as greatly affected by purification of the solutions as in acidic media [45]. Since the earlier RRDE experiments, it has been shown that H2O2 is the main product of the reduction in the activation domain but is not detected anymore at lower potentials, when the electrode reaction is limited by mass transport [59, 64, 65]. The existence of two potential regions for ORR in alkaline media is also illustrated by the Tafel plots, as those reported in Fig. 6 [66]. The existence of two... 

Figure 3 Plots of the total number of electrons Ut (a), of the Tafel slope b (b), of the limiting current density IjA,-, (c) and of the exchange current density I/A (d), versus the platinum loading for the reduction of oxygen on a platinum-modified polyaniline-glassy carbon rotating disk electrode (O2 saturated 0.5 M H2SO4 2mVs 25 °C A, is the true surface...

From the plots, it is seen that the corrosion current increases as the angular velocity increases from 0 to 30. However, when the velocity is increased further, the reduction of oxygen becomes activation controlled. As a result, the corrosion rate becomes independent of velocity. Table 3.5 summarizes the corrosion current and the corrosion potential as a frmction of electrolyte angular velocity. The data were taken from Fig. 3.18. (b) To estimate the corrosion current and the corrosion potential when sacrificial Zn-Mn alloy is short circuited with iron, the anodic Tafel line for Zn-Mn sacrificial alloy is plotted in Fig. 3.19. The point of intersection of the Zn-Mn dissolution line and cathodic oxygen Tafel line provides the value of the galvanic current (GC) or impressed current (IC) and the corrosion potential. 

E3.6. A lead electrode is immersed in an oxygen-saturated 0.1 M PbS04 solution. Calculate and plot the corrosion current at pH between 3 and 6. The Tafel constants are b = — fcc = 0.10V/decade and the exchange current densities for lead and oxygen reduction are 10 and 10 A/cm, respectively. 

It can be seen that a plot of / vs should be linear, and the intercept can be used to calculate k. Moreover, the slopes of these plots, d / /dco , should be independent of potential, while the intercepts (because of k) vary strongly with potential. Indeed log k vs E is form of Tafel plot and should therefore be linear. Fig. 4.11 shows a set of vs plots constructed from data for the reduction of oxygen on an aluminium brass [5]. 

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