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Fig. 4. Cyclic voltammogram obtained on a rotating disk electrode. Electrode area 0.125cm?. Scan rate 10mVs~'. Rotation rate 600 rpm. Electrodeposition of copper-selenium binaries in a citric acid medium

Figure 4 Cyclic voltammogram obtained on a rotating disk electrode. Electrode area 0.125cm?. Scan rate 10mVs~'. Rotation rate 600 rpm. Electrodeposition of copper-selenium binaries in a citric acid medium

Related Figures (14)

Fig. 1. Cyclic voltammograms obtained on a motionless electrode. [Cu(II] = 10-3 M, 10-* < [Se(IV)] < 1.2x 10°3M. Electrode area 0.125cm?. Scan rate 50mVs_}.
Fig. 1. Cyclic voltammograms obtained on a motionless electrode. [Cu(II] = 10-3 M, 10-* < [Se(IV)] < 1.2x 10°3M. Electrode area 0.125cm?. Scan rate 50mVs_}.
Fig. 2. Cyclic voltammograms obtained on a motionless electrode. [Cu(II] = 10-3 M, 10°* < [Se(IV)] < 1.2.x 1073M. Electrode area 0.125cm?: Scan rate 10mVs—?. The anodic peak Ila and the hump IIIa on the positive side are clearly related to the formation of copper selenides. There is presumably a codeposition of selenium with copper at the beginning of the reduction voltammogram: the anodic oxidation of a
Fig. 2. Cyclic voltammograms obtained on a motionless electrode. [Cu(II] = 10-3 M, 10°* < [Se(IV)] < 1.2.x 1073M. Electrode area 0.125cm?: Scan rate 10mVs—?. The anodic peak Ila and the hump IIIa on the positive side are clearly related to the formation of copper selenides. There is presumably a codeposition of selenium with copper at the beginning of the reduction voltammogram: the anodic oxidation of a
Fig. 3. Voltammograms obtained on a rotating disk elec- trode. [Cu(I1)] = 10-3 M, 1074 < [Se(IV)] < 12x 10°3M. Electrode area 0.125cm?. Scan rate 10mVs—i.
Fig. 3. Voltammograms obtained on a rotating disk elec- trode. [Cu(I1)] = 10-3 M, 1074 < [Se(IV)] < 12x 10°3M. Electrode area 0.125cm?. Scan rate 10mVs—i.
Fig. 5. Variation of J,;,, VS. Jo for various selenium(IV) concentrations. It may be shown that for any deposition mecha- nism, the total limiting current density is given by the relation: In Fig. 5 are plotted the variations of the limiting current densities J,,,, (measured at —0.8V vs. mse) vs. Jo for various values of [Se(IV)].o (10 > r > 1.67). w is the angular velocity of the rotat- ing disk. A linear variation is observed, indicating that the global process is diffusion controlled. Fur- thermore, in Fig. 6 is plotted the variation of J\,,/ Jo vs. [Se(IV)],o:. In this case a linear variation is also observed. It will be shown later that mixed deposits of copper and cuprous selenide or of cuprous selenide and cupric selinide are obtained in these potential and concentration ranges.
Fig. 5. Variation of J,;,, VS. Jo for various selenium(IV) concentrations. It may be shown that for any deposition mecha- nism, the total limiting current density is given by the relation: In Fig. 5 are plotted the variations of the limiting current densities J,,,, (measured at —0.8V vs. mse) vs. Jo for various values of [Se(IV)].o (10 > r > 1.67). w is the angular velocity of the rotat- ing disk. A linear variation is observed, indicating that the global process is diffusion controlled. Fur- thermore, in Fig. 6 is plotted the variation of J\,,/ Jo vs. [Se(IV)],o:. In this case a linear variation is also observed. It will be shown later that mixed deposits of copper and cuprous selenide or of cuprous selenide and cupric selinide are obtained in these potential and concentration ranges.
Fig. 6. Variation of the limiting current density vs. the selenium(IV) concentration [Cu(II] = 10°>M. Potential —0.8 V vs. mse. where m, is the mass transfer coefficient of the species i. In the case of a rotating disk electrode, the value of m, is given by[9]:
Fig. 6. Variation of the limiting current density vs. the selenium(IV) concentration [Cu(II] = 10°>M. Potential —0.8 V vs. mse. where m, is the mass transfer coefficient of the species i. In the case of a rotating disk electrode, the value of m, is given by[9]:
Table 1. Calculated values of no, and ng, at different applied potentials
Table 1. Calculated values of no, and ng, at different applied potentials
Fig. 7. Variation of the limiting current density measured on the reverse curves, vs. the selenium(IV) concentration, at various potentials.
Fig. 7. Variation of the limiting current density measured on the reverse curves, vs. the selenium(IV) concentration, at various potentials.
Table 2. Chemical composition in films formed in various conditions of electro- deposition potential and solution compositions. The chemical composition was determined by polarography (P) or by X-ray fluorescence (X)
Table 2. Chemical composition in films formed in various conditions of electro- deposition potential and solution compositions. The chemical composition was determined by polarography (P) or by X-ray fluorescence (X)
Fig. 8. Chemical compositions present in films formed at ~—0.4 and —0.5 V vs. the ratio r. Electrodeposition of copper-selenium binaries in a citric acid medium
Fig. 8. Chemical compositions present in films formed at ~—0.4 and —0.5 V vs. the ratio r. Electrodeposition of copper-selenium binaries in a citric acid medium
Fig. 9. Chemical compositions and phases present in films formed at —0.6 and —0.8V vs. the ratio r. The nature of the phases was determined by X-ray diffractommetry (XRD) and by anodic oxidation (AO). The presence of sele- nium has not been directly evidenced.
Fig. 9. Chemical compositions and phases present in films formed at —0.6 and —0.8V vs. the ratio r. The nature of the phases was determined by X-ray diffractommetry (XRD) and by anodic oxidation (AO). The presence of sele- nium has not been directly evidenced.
Fig. 10. Scanning anodic oxidation of films prepared at —0.8 V for various values of R. The oxidation was made in an electrolyte containing only 0.4M citric acid. Scan rate ImVs7'.
Fig. 10. Scanning anodic oxidation of films prepared at —0.8 V for various values of R. The oxidation was made in an electrolyte containing only 0.4M citric acid. Scan rate ImVs7'.
Fig. 11. Scanning cathodic reduction of films prepared at —0.6V for various values of R. The reduction was made in an electrolyte containing only 0.4M citric acid. Scan rate IimVs"?.
Fig. 11. Scanning cathodic reduction of films prepared at —0.6V for various values of R. The reduction was made in an electrolyte containing only 0.4M citric acid. Scan rate IimVs"?.
Fig. 12. Scanning anodic oxidation of non-reduced and prereduced films for various values of R. Scan rate ImVs-t. The results presented in the previous section show strong evidence for the control of the deposit com- position by a diffusion process. Between —0.6 and —0.8V vs. mse, the voltammograms obtained on a rotating disk electrode show a well defined plateau, the variations of the currents vs. the square root of the angular velocity of the electrode are linear and the solid phase composition is linearly related to the
Fig. 12. Scanning anodic oxidation of non-reduced and prereduced films for various values of R. Scan rate ImVs-t. The results presented in the previous section show strong evidence for the control of the deposit com- position by a diffusion process. Between —0.6 and —0.8V vs. mse, the voltammograms obtained on a rotating disk electrode show a well defined plateau, the variations of the currents vs. the square root of the angular velocity of the electrode are linear and the solid phase composition is linearly related to the
Table 3. The composition of the formed phases, for various deposition potentials and various solu- tion compositions ratio of the solution composition by the expression (20). Using the diffusion layer approximation, the flux of a species X is then given by the expression: For the potentials more negative than ~—0.8 V vs. mse, the composition of the deposit is no longer determined by the ratio of the arriving fluxes. For any composition of the solution, only cuprous sele- nide is obtained as a solid phase. This is due to the fact that the cupric selenide or the cupric + cuprous selenide mixtures Cu,Se are not stable and are reduced into cuprous selenide by a reaction of the type: Electrodeposition of copper—selenium binaries in a citric acid medium
Table 3. The composition of the formed phases, for various deposition potentials and various solu- tion compositions ratio of the solution composition by the expression (20). Using the diffusion layer approximation, the flux of a species X is then given by the expression: For the potentials more negative than ~—0.8 V vs. mse, the composition of the deposit is no longer determined by the ratio of the arriving fluxes. For any composition of the solution, only cuprous sele- nide is obtained as a solid phase. This is due to the fact that the cupric selenide or the cupric + cuprous selenide mixtures Cu,Se are not stable and are reduced into cuprous selenide by a reaction of the type: Electrodeposition of copper—selenium binaries in a citric acid medium
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