Platinum Tafel plots

Figure 4. Log intensity vs. potential plots (Tafel plots) obtained from the voltammograms of a platinum electrode submitted to a 2 mV s l potential sweep polarized in a 0.1 M LiC104 acetonitrile solution having different thiophene concentrations. (Reprinted from T. F. Otero and J. Rodriguez, Parallel kinetic studies of the electrogeneration of conducting polymers mixed materials, composition, and kinetic control. Electrochim, Acta 39, 245, 1994, Figs. 2, 7. Copyright 1997. Reprinted with permission from Elsevier Science.)...

Worked Example 7.5. The one-electron reduction of the heptyl viologen dication (HV +) (to form the radical cation HV+ ) occurs at a platinum electrode with an area of 1.50 cm. Calculate the value of kd, given that the intercept on a Tafel plot of log / (as y ) against tj (as x ) is —2.2. 

This leads to a Tafel slope of b = 2.3RT/PF = - 0.12 V for P = 0.5, and a reaction order (at constant potential) of unity. The transfer coefficient is equal to the symmetry factor P as in the case of mercury, but we recall that the Tafel slope is calculated here assuming essenti illy full coverage, whereas that on mercury was obtained assuming a very low value of the coverage. The Tafel plot observed on platinum in acid solutions is shown in Fig. 5F. 

Fig. 5F Tafel plots obsen ed for the h.e.r. on platinum in acid solutions at low overpotentials, where the slope is close to - 30 inVIdecade. Data based on Adzic, Spasojevic and Despic Electrochim. Acta, 24, 569, 1979).

Fig-1 Some of the first published comparative current-potential (Tafel) plots obtained by Bowden and Rideal [2, 4]. I. Mercury. II. Platinized mercury, 1/100 covered. III. Platinized mercury, thin film of Pt. IV. Etched silver, new. V. Etched silver, old. VI. Polished silver. VII. Bright platinum. 

FIGURE 1.2 Tafel plots as electrode potential, E, versus the logarithm of the current density, logy, for mercury ( - ), platinized mercury to 1% (o-o), platinized mercury as thin film (a-a), fresh etched silver ( - ), aged etched silver (O-O), polished silver ( - ), bright platinum (H—h), and spongy platinum electrodes (c-c). 

A rotating platinum disk electrode was used for gathering data for the calculation of the kinetic constants. Tafel plots (5) were developed (Figure 2), from which the heterogeneous rate constants, k , and the electron-transfer coefficients, a, were determined. In all determinations of kinetic parameters, a blank voltammogram, run under identical conditions, was subtracted from the data to remove current due to background reactions or charging of the double layer. 

Figure 2. Tafel plots of oxidation and reduction of iron at pH 3 in 0.1 m KCl determined at a rotating platinum disk electrode. Currents are extrapolated values for an infinite rate of rotation. Temperature = 298 1 K.

Table H. Heterogeneous electron-transfer kinetics at the platinum disk electrode at 298 K. All values determined from linear portions of Tafel plots at rates of rotation extrapolated to infinity. Reaction of Se and As too slow for observation...

Figure 10.8 Tafel plots of the electrocatalytic oxidation of 0.1 M formic acid in 0,1 M HCIO4 at different platinum-based alloy electrodes dispersed in a polyaniline film and containing 0,1 mg cm of platinum (—) Pt (---) Pt-Ru (...) Pt-Sn (—) Pt-Ru-Sn. (Reprinted with permission from ref 69)...

If a piece of platinum wire is coupled to zinc which is corroding in an air-free, acidic solution, vigorous hydrogen evolution begins on the platinum surface and the rate of zinc dissolution also increases. In terms of polarization curves (Fig. 14.10), the corrosion rate is /corr(Zn), which is obtained as the point of intersection of the Zn dissolution and hydrogen evolution Tafel plots. The corrosion potential is represented by Fcorr-... 

Tafel plots for a single type of SAM with pendant pyRu(NH3)s redox molecules have been acquired using gold, platinum, and silver electrodes [236]. The reorgani2a-... 

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.)...

To compare the specific activity (is) of the different catalysts for ORR, mass-transfer corrected Tafel plots of kinetic current densities based on the active area of platinum were evaluated. For such an evaluation, the prerequisite factor, namely, the chemically active surface area of Pt (EAA) for all catalysts was determined by using the following equations ... 

Fig. 82. Anodic Tafel plots for the O2 evolution and cathodic plots for the O2 reduction on rhodium (O), iridium ( + ), platinum-40 at. % rhodium (x), and platinum (A) in 1 M...

DC polarisation tests took place in a three-electrode electrochemical cell where the area of the working electrode (modified Al-2024 T3) exposed to the corrosive solution was 1 cm. For these measurements, a platinum foil and a SCE were used as the counter and the reference electrodes, respectively. Potentiodynamic tests were carried out by scanning the potential between -1 V and 0 V vs SCE at a rate of 1 mV s. The resulting graphics were fitted to the Tafel plots allowing the corrosion current and potential, and the polarisation resistance to be extrapolated. Corrware software was used for fitting. 

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].)...

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