Cathodic polarization curves electrodeposition

Yamashita and co-workers studied the effects of ultrasound on the electrodeposition of Zn from ZnBr2 solution [92], They examined the effects of ultrasound on the cathodic polarization curves and the impedance characteristics of the system. From their results, it was shown that ultrasound increased the reaction rates of deposition and dissolution of Zn. However, ultrasound had no effect on the overpotential of the reaction. Electron microscopy studies also showed that uniform and fine crystals of Zn were obtained in the presence of ultrasound, thus increasing hardness of the coating. 

FIGURE 20.5 A typical cathodic polarization curve of zinc electrodeposition in the solution used for this study. 

Mishra et al. [198] discussed in an exemplary way the dark and photocorrosion behavior of their SnS-electrodeposited polycrystalline films on the basis of Pourbaix diagrams, by performing photoelectrochemical studies in aqueous electrolytes with various redox couples. Polarization curves for the SnS samples in a Fe(CN) redox electrolyte revealed partial rectification for cathodic current flow in the dark, establishing the SnS as p-type. The incomplete rectification was... 

The electrodeposition of an alloy requires, by definition, the codeposition of two or more metals. In other words, their ions must be present in an electrolyte that provides a cathode film, where the individual deposition potentials can be made to be close or even the same. Figure ll.l depicts typical polarization curves, that is, deposition... 

These curves were obtained experimentally for Pt electrodeposited onto the monocrystalline, macro- and mesoporous silicon surfaces. There are two peaks corresponding to the oxidation of adsorbed hydrogen, a potential area of a double layer, and an area of the oxygen adsorption. The current increase at the potential of 1.45 V and higher is associated with the release of molecular oxygen. In the cathodic polarization, peaks concerned with the reduction of adsorbed oxygen, a feebly marked potential area of the double layer, and a maximum of the hydrogen adsorption are observed. 

The preconcentration of trace metals by electrodeposition is an integral part of anodic-stripping voltammetry. The method consists of the preelectrolysis of the stirred solution with a small mercury drop or solid electrode as the cathode (112-114). The metals, which are deposited and dissolve in the mercury, are then stripped from the amalgam after a suitable rest period by a reversal of the electrode potential. The resulting current-polarization curve is characteristic of the metal and its concentration. Concentrations as low as 10 M of metal ions require a preelectrolysis of about 60 min or longer. Other electrodes such as mercury films, platinum, gold, silver, and various forms of carbon have been used (77 ). 

Fig. 1.9 (a) The polarization curve for Zn electrodeposition from 0.10 M ZnS04 in 2.0 M NaOH and the typical surface morphologies obtained at overpotentials of (b) = 45 mV (the zone of the fast increase in the current density with increasing overpotential) and (c) = 100 mV (the plateau of the limiting diffusion current density). The cathodic current densities in Fig. 1.9a are taken as positive ones (Reprinted from Ref. [21] with permission from the Serbian Chemical Society)... 

Fig. 1.11 The polarization curves for Cu electrodeposition from (a) 0.075, 0.30, and 0.60 M CUSO4 in 0.50 M H2SO4 (b) 0.15 M CUSO4 in 0.125, 0.25, and 1.0 M H2SO4 and (c) 0.15 M CUSO4 in 0.50 M H2SO4. Temperatures 14.0, 35.0, and 50.0 0.5 °C. The cathodic current densities are taken as positive ones (Reprinted from Ref [25] with permission from MDPI, Ref [26] with permission from Elsevier, Ref [27] with permission from the Serbian Chemical Society and Ref [7] with kind permission from Springer)...

Application of complex salt electrolytes in metal electrodeposition processes was examined by comparison of silver electrodeposition processes from the simple (nitrate) and complex (ammonium) electrolytes [15]. Silver was deposited from 0.10 M AgNOs in 0.20 M HNO3 (the simple electrolyte) and 0.10 M AgNOs in 0.50 M (NH4)2S04 to which was added ammonium hydroxide to dissolve the precipitate of Ag sulfate (the complex electrolyte). The conductivities of both electrolytes were almost the same [3]. Silver was deposited onto a stationary vertical Pt cathode (1x1) cm placed in the middle of a cylindrical cell (diameter 6 cm and height 5 cm). The surface of the cell was covered by anode of a high purity Ag plate. Polarization curves were recorded at the Pt wire electrodes at which Ag from the ammonium complex electrolyte was previously electrodeposited. 

This is the general behavior that may be expected whenever there are two possible reactions in a given potential range. Most of the time in metal electrodeposition, these two reactions are the reduction of metal cations and the discharge of hydrogen ions, but other cathodic processes are also possible, e.g., the discharge of dissolved oxygen. A similar behavior is to be expected in the electrodeposition of binary alloys when the difference between the equilibrium potential of the two metal redox couples is remarkable. The typical shape of the polarization curve as briefly discussed... 

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