Thin films of normalNiCo and normalCoFe have been galvanostatically electroplated onto a platinum rotating disk electrode from simple sulfate baths containing 0.5M of the more noble metal sulfate and 0.1M of the less noble metal sulfate. The experimental results are compared to those of previous studies of normalNiFe codeposition in order to study the anomalous codeposition behavior of the binary iron‐group alloys. Comparison of the electrodeposition results indicates that codeposition of these binary alloys is not totally analogous. It was found that codepositions of normalNiCo and normalNiFe show more mass‐transfer effects than does normalCoFe deposition within the range of current densities studied. A model of anomalous codeposition put forth previously for normalNiFe was applied to the electrodeposition of normalNiCo and normalCoFe to determine the extensibility of the model, which assumes metal monohydroxides, MOH+ , are the important charge‐transfer species. This model was unable to characterize fully either normalNiCo or normalCoFe electrodeposition. However, with minor changes to the hydrolysis constants used in the model, the model predictions were found to agree with the data for normalCoFe codeposition and greatly improve the fit for the normalNiCo results.

Thin films of the iron-group elemental metals (Ni, Co, and Fe, group VIIIB) and binary alloys (NiCo, CoFe, and NiFe) were galvanostatically electroplated onto a platinum rotating disk electrode from simple sulfate baths. In all cases, the increasing electrode rotational rate was found to decrease the partial current densities at a given cathodic potential. Experimental results indicate that for electrodeposition: two distinct rate-determining steps exist, partial current densities for metal deposition are not linearly related to bulk metallic concentration, and the partial current densities for hydrogen evolution are found to reach a plateau for each metal sulfate bath and rotational rate studied. For the conditions studied, comparison of the partial current densities for elemental and alloy deposition shows that the more noble metal deposition is unchanged or inhibited in alloy codeposition, while that for the less noble metal is promoted.

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A mechanism of iron-group elemental metal and binary alloy electrodeposition is proposed. The one-dimensional diffusion model of Grande and Talbot is used to determine near-surface concentrations of the ionic species deemed important for electrodeposition; the current model expands upon the surface kinetics by including the effects of competitive adsorption, site blockage by hydrogen atoms, and a variance in the number of adsorption sites. Fitting of the model kinetic parameters to the elemental electrodeposition data was found to simulate the partial current densities extremely well. The proposed model was found to be extensible to the irongroup binary alloys. Use of the elemental electrodeposition parameters in alloy codeposition was found to effectively characterize the experimental results, e.g., partial current densities, weight fractions, and the effect of electrode rotational rate.