Mass Transfer of Protons during Electrodeposition of Cobalt in Chloride Electrolytes

Abstract

In acid cobalt chloride electrolytes, the electrodeposition of cobalt and the evolution of hydrogen take place simultaneously. On a rotating platinum disk electrode, the current efficiency for cobalt deposition was calculated based on the anodic charge needed for stripping of the cobalt deposits divided by the total cathodic charge. The results showed a decrease in current efficiency with increasing rotation rate. From the partial current density for hydrogen evolution, the diffusion coefficient for protons was calculated. The derived diffusion coefficients varied with overpotential and pH but were always 1 order of magnitude lower compared to what was expected from literature values. This was attributed to water drag when transporting cobalt ions toward the electrode. The variations in the calculated diffusion coefficients were explained by the change in the transfer number when the proton concentration was changed and in the potential gradient when the potential was varied.

Kinetical study about the cobalt electrodeposition onto polycrystalline platinum

“…[1][2][3][4][5][6][7] Most CoL have been prepared employing molecular beam sputtering, 8 evaporation techniques, 9,10 and more recently, electrodeposition. [11][12][13][14][15][16][17][18][19][20][21] Although it is well known that electrodeposition contributes to achieving reliable and inexpensive methods to produce CoL on metallic substrates, [22][23][24][25] to the best of our knowledge, few studies have considered Co electrodeposition on Pt electrodes. [11][12][13][14][15][16][17][18][19][20][21] Most of these studies have been conducted from sulfate and chloride ammoniacal solutions.…”

“…[11][12][13][14][15][16][17][18][19][20][21] Although it is well known that electrodeposition contributes to achieving reliable and inexpensive methods to produce CoL on metallic substrates, [22][23][24][25] to the best of our knowledge, few studies have considered Co electrodeposition on Pt electrodes. [11][12][13][14][15][16][17][18][19][20][21] Most of these studies have been conducted from sulfate and chloride ammoniacal solutions. [11][12][13][14][15][16][17][18][19][20][21] Perhaps the main advantage of using chloride plating baths rather than sulfate electrolytes is its higher electrical conductivity at lower overpotentials during Co electrodeposition.…”

“…[11][12][13][14][15][16][17][18][19][20][21] Most of these studies have been conducted from sulfate and chloride ammoniacal solutions. [11][12][13][14][15][16][17][18][19][20][21] Perhaps the main advantage of using chloride plating baths rather than sulfate electrolytes is its higher electrical conductivity at lower overpotentials during Co electrodeposition. 12 However, the stress added to the Co deposits when using chloride solutions is larger than that when using sulfate solutions.…”

“…12 The current efficiency decreases when the rotating rate of the electrode is augmented. 13 Although such studies are important for the development of new methods to generate CoL, the kinetics of Co electrodeposition has not been analyzed. Increased understanding of the nucleation and growth parameters involved during Co electrodeposition on Pt from chloride plating baths would allow the generation of Co films with reproducible characteristics and specific properties.…”

Proton Transport during Electrodeposition of Cobalt in Chloride Electrolytes

“…Earlier work has described the influence of pH, cobalt concentration, temperature, chloride concentration and sulphate addition by different kinetic parameters on cobalt electrodeposition [1][2][3]. During this work a decrease in current efficiency for cobalt deposition with increasing rotation rate was observed, and this was studied in more detail.…”