Selectivity Tafel plot

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 3.5 (a) A typical potentiodynamic polarization plot for a Co electrode, graphically analyzed to determine E on and icon- (b) and (c) display coupled Tafel plots recorded in selected slurry solutions for the Co—A1 and Cu—Ta bimetallic systems, respectively. The juncture point (p) of the two plots in (h) corresponds to the galvanic parameters g and ig for the Co—A1 galvanic system. The plots in (c) represent a reversal of conventional galvanic polarities, where there are two crossover points (pi and P2). In all cases of (a), (b), and (c), the potential was scanned at a speed of 5 mV/s. 

Tafel plots, effect of anions (SO4 and CIO4 ) and reaction order allowed determination that nitrate adsorption (Fig. 2, reaction 1) and nitrate to nitrite reduction (Fig. 2, reaction 2) were the rate determining steps, whereas the conversion of N02 to NO is fast. Subsequent steps will determine the selectivity. For the different metals... 

Surface concentrations of complex species and ligands can be determined by means described in Chapter 3 further, the normalized Tafel plots (NTPs) can be obtained. However, initially, we shall make use of isosurface concentration voltammetry presented in Section 5.3.1. Using experimental data obtained at constant surface concentrations, one can estimate the value of without any tentative assumptions as to the mechanism of the charge transfer step, that is, for unknown composition of the EAC. It follows from Eq. (4.3) that for t/r = const, the surface concentrations of the components do not depend on time. Selected in this way, data (Figure 8.7) are satisfactorily approximated by the lines with similar slopes, which yield = 0.37 0.03 (see Eq. (8.17)). This value canbe checked by the analysis of individual transients of the potential, but then the composition of the EAC must be established. 

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