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Fig. 1. Cyclic voltammograms of tungsten rotating disc electrode in 0.08 M KOF solution supported by 0.25 M KSO,. Polarization rate was 50 mV s!.

Figure 1 Cyclic voltammograms of tungsten rotating disc electrode in 0.08 M KOF solution supported by 0.25 M KSO,. Polarization rate was 50 mV s!.

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Fig. 2. Cyclic voltammograms of tungsten rotating disc electrode in unsupported 0.08 M KOH solution. Polarization rate was 50 mV s~'.
Fig. 2. Cyclic voltammograms of tungsten rotating disc electrode in unsupported 0.08 M KOH solution. Polarization rate was 50 mV s~'.
Fig. 3. The Levich plots for anodic dissolution of tungsten in KOH solutions of selected concentrations (M): ™ — 0.02; @ - 0.04; A - 0.06; W - 0.08; < - 0.10, supported by 0.25 M K,SO,. The limiting currents, at the potential of 1.2 V, were used to make the plots. In order to check the quantitative correspondence of Eq. (4) to the assumption that only OH™ ions are responsible for mass trans- fer limitation of anodic dissolution of tungsten, the diffusion coef- ficient of OH ions at infinite dilution, amounting to 5.27 x 10°> cm? s~! [34], and n=1, were used to calculate the depen- dence j, vs. 1? according to the Eq. (4). As one can see in Fig. 5, the slope of the calculated dependence is considerably higher than the one determined experimentally for anodic dissolution of
Fig. 3. The Levich plots for anodic dissolution of tungsten in KOH solutions of selected concentrations (M): ™ — 0.02; @ - 0.04; A - 0.06; W - 0.08; < - 0.10, supported by 0.25 M K,SO,. The limiting currents, at the potential of 1.2 V, were used to make the plots. In order to check the quantitative correspondence of Eq. (4) to the assumption that only OH™ ions are responsible for mass trans- fer limitation of anodic dissolution of tungsten, the diffusion coef- ficient of OH ions at infinite dilution, amounting to 5.27 x 10°> cm? s~! [34], and n=1, were used to calculate the depen- dence j, vs. 1? according to the Eq. (4). As one can see in Fig. 5, the slope of the calculated dependence is considerably higher than the one determined experimentally for anodic dissolution of
Fig. 4. The Levich plots for anodic dissolution of tungsten in unsupported KOH solutions of the following concentrations (M): ml - 0.02; @ - 0.04; @ - 0.06; w - 0.08; < - 0.10. The limiting currents, at the potential of 1.5 V, were used to make the plots.
Fig. 4. The Levich plots for anodic dissolution of tungsten in unsupported KOH solutions of the following concentrations (M): ml - 0.02; @ - 0.04; @ - 0.06; w - 0.08; < - 0.10. The limiting currents, at the potential of 1.5 V, were used to make the plots.
Fig. 5. The Levich plot of rotating tungsten disc electrode in unsupported (@) and supported (0.25 M K2SO,) (gg) 0.1 M KOH solution. Triangles (a) present the points calculated on the basis of Levich equation (4) under assumption that the diffusion of OH™ ions only limits the anodic dissolution of tungsten (n=1); the diffusion coefficient of OH™ ions at infinite dilution, D = 5.26 x 10-° cm? s~!, was used for the calculation. In addition to the Levich analysis, the apparent reaction order with respect to OH” ions was determined from the slope of the
Fig. 5. The Levich plot of rotating tungsten disc electrode in unsupported (@) and supported (0.25 M K2SO,) (gg) 0.1 M KOH solution. Triangles (a) present the points calculated on the basis of Levich equation (4) under assumption that the diffusion of OH™ ions only limits the anodic dissolution of tungsten (n=1); the diffusion coefficient of OH™ ions at infinite dilution, D = 5.26 x 10-° cm? s~!, was used for the calculation. In addition to the Levich analysis, the apparent reaction order with respect to OH” ions was determined from the slope of the
Fig. 7. The dependence log j, vs. log c(OH) for tungsten rotating disc electrode ir unsupported and K2SO,4 supported KOH solutions, at the following concentrations (M) of K2SO, supporting electrolyte: Mi - 0.50; @ - 0.25; & - 0.10; Ww - 0.05; <« - 0.00. Empty circles present the data calculated by means of Levic equation (4) unde! assumption that the diffusion of OH ions only limits the anodic dissolution o! tungsten (n=1); the diffusion coefficient of OH” ions at infinite dilution D=5.26 x 10-° cm? s~', was used for the calculation. A common rotation rate o 1800 rpm holds for all points.
Fig. 7. The dependence log j, vs. log c(OH) for tungsten rotating disc electrode ir unsupported and K2SO,4 supported KOH solutions, at the following concentrations (M) of K2SO, supporting electrolyte: Mi - 0.50; @ - 0.25; & - 0.10; Ww - 0.05; <« - 0.00. Empty circles present the data calculated by means of Levic equation (4) unde! assumption that the diffusion of OH ions only limits the anodic dissolution o! tungsten (n=1); the diffusion coefficient of OH” ions at infinite dilution D=5.26 x 10-° cm? s~', was used for the calculation. A common rotation rate o 1800 rpm holds for all points.
Fig. 6. The limiting diffusion current density in function of concentration of OH™ ions for tungsten rotating disc electrode in KOH solutions, for the following concentrations (M) of supporting electrolyte K2SO,: Ml - 0.50; @ - 0.25; 4 - 0.10; W - 0.05; <q - 0.00. Opened circles (O) present the data calculated by means of Levich equation (4) under assumption that the diffusion of OH” ions only limits the anodic dissolution of tungsten (n=1); the diffusion coefficient of OH™ ions at infinite dilution, D = 5.26 x 10~> cm? s~', was used for the calculation. A common rotation rate of 1800 rpm holds for all points.
Fig. 6. The limiting diffusion current density in function of concentration of OH™ ions for tungsten rotating disc electrode in KOH solutions, for the following concentrations (M) of supporting electrolyte K2SO,: Ml - 0.50; @ - 0.25; 4 - 0.10; W - 0.05; <q - 0.00. Opened circles (O) present the data calculated by means of Levich equation (4) under assumption that the diffusion of OH” ions only limits the anodic dissolution of tungsten (n=1); the diffusion coefficient of OH™ ions at infinite dilution, D = 5.26 x 10~> cm? s~', was used for the calculation. A common rotation rate of 1800 rpm holds for all points.
Fig. 8. Hydrodynamic chronoamperometric curves of tungsten rotating disc electrode in both supported (0.5 M K2SO,) (C1) and unsupported (O) KOH solution at a common rotation rate of 1800 rpm. The working potential was fixed within the region of anodic current plateau (1.5 V). The current jumps correspond to the moments when KOH portions were injected.
Fig. 8. Hydrodynamic chronoamperometric curves of tungsten rotating disc electrode in both supported (0.5 M K2SO,) (C1) and unsupported (O) KOH solution at a common rotation rate of 1800 rpm. The working potential was fixed within the region of anodic current plateau (1.5 V). The current jumps correspond to the moments when KOH portions were injected.
Fig. 9. The dependence of limiting current of tungsten electrodissolution on OH concentration, in both supported (0.5 M K2SO,) (squares) and unsupported (circles) KOH solution, recorded at a rotation rate of 1800 rpm. Empty symbols present the voltammetric data, and filled symbols present the chronoamperometric data.
Fig. 9. The dependence of limiting current of tungsten electrodissolution on OH concentration, in both supported (0.5 M K2SO,) (squares) and unsupported (circles) KOH solution, recorded at a rotation rate of 1800 rpm. Empty symbols present the voltammetric data, and filled symbols present the chronoamperometric data.
Related topics:
Analytical ChemistryElectroanalytical ChemistryRotating Disc Electrode
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