Rotating disk electrode experimental measurements

Figure 8.12 Relationships between the catalytic properties and electronic structure of Pt3M alloys correlation between the specific activity for the oxygen reduction reaction measured experimentally by a rotating disk electrode on Pt3M surfaces in 0.1 M HCIO4 at 333 K and 1600 lev/min versus the li-band center position for (a) Pt-skin and (b) Pt-skeleton surfaces. (Reprinted with permission from Stamenkovic et al. [2007b]. Copyright 2007. Nature Pubhshing Group.)...

The first voltammetric methods met are stationary voltammetries performed on a dropping mercury electrode (polarography) or on a solid rotating disk electrode. The limiting current measured is directly proportional to the concentration of the electroactive species in the solution. Experimental potential scan rate is lower than lOrnVs-1. 

The principle of the experimental arrangement devised for the transfer-fimction measurements involving a nonelectrical input quantity was given previously in Figures 14.2 and 14.3. In this section, a few examples are presented. The transfer function corresponding to the response of the electrochemical system to a perturbation of the rotation speed of a rotating disk electrode is given in Chapter 15. 

From the experimental point of view, for reductions, DC-polarography at the dropping mercury electrode (DME) or cyclic voltammetry (CV) at the hanging mercury drop electrode (HMDE) were used and for controlled-potential electrolyses at negative potentials, a mercury pool electrode was employed. For both oxidative and reductive experiments, voltammetry at the platinum rotating disk electrode (RDE) and CV at the stationary platinum electrode were applied. All experiments were performed in a three-electrode system with a platinum counter electrode. For measurements in analytical scale (a standard aminocarbene concentration was 3x 10-" mol/1), an undivided cell for 5-10 ml was used and for preparative electrolyses a two-compartment cell of the H-type was employed [14]. The potentials were referred to the saturated calomel electrode (SCE), which was separated from the investigated solution by a double-frit bridge. 

Figure 1. Schematic of experimental setup for measurements of the rotating ring-disk electrode (1) dual potentiogal-vanostat (2) ZnO disk electrode (3) Pt ring electrode (4) Teflon electrode holder (5) electrolytic cell (6) N2 gas inlet (7) Pt counter electrode (8) SCE (9) mirror ...

These relative surface excess parameters can be determined experimentally using different methods /)(w) can be determined by radiotracer studies, o-measurements, electroanalytical techniques (twin-electrode thin-layer, flow-through thin layer, rotating ring-disk experiments) etc., whereas q can be determined by charging curves, capacitance measurements etc. Isotherm conversion q-Fiiyf) is obtained by the corresponding Maxwell relations ... 

Two additional experimental factors are important when the RDE is used to determine diffusion coefficients. First, the Levich equation assumes that the disk is centered on ihe axis of rotation. Any non-idealities in the construction of the RDE will result in an increase in the measured current, and thus lead to an overestimation of D. Second, edge effects can be present, particularly at very low rotation rates and/or with very small electrodes. These effects will be apparent as non-linearities in the vs. ry plot, and therefore rotation rates at which these non-linearities occur should not be used for the determination of the diffusion coefficient. 

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