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- Title
Detection and characterization of molybdenum oxides formed during the initial stages of cobalt–molybdenum electrodeposition.
- Authors
Gomez, E.; Pellicer, E.; Valles, E.
- Abstract
The initial stages of cobalt-molybdenum electrodeposition on a vitreous carbon electrode were studied to obtain information about the mechanism of cobalt-molybdenum induced codeposition. Solutions containing cobalt sulphate, sodium molybdate and sodium citrate at pH 6.6 were used. A first step in the mechanism of alloy deposition is proposed. This step takes into account the formation of molybdenum(iv) oxides over which Co-Mo alloy may be only deposited if sufficient potential is applied. Co-Mo electrodeposition occurs through an early stage involving low reduction current, related to the formation of molybdenum oxides, followed by a later stage in which the reduction current suddenly increases, corresponding to alloy codeposition. When a low potential is applied, a continuous coloured molybdenum oxide film is formed on the electrode and Co-Mo is not deposited. To induce the alloy deposition on the `oxide film' it is necessary to apply more negative potentials than a threshold value, which depends on the composition of the electrolytic bath. By increasing molybdate concentration in solution, the `threshold potential' shifts to more negative values. intermediate molybdenum oxides were characterized using scanning electron microscopy (SEM), compositional analysis, Raman measurements and Auger and X-ray photoelectron spectroscopies. The initial stages of cobalt-molybdenum electrodeposition on a vitreous carbon electrode were studied to obtain information about the mechanism of cobalt-molybdenum induced codeposition. Solutions containing cobalt sulphate, sodium molybdate and sodium citrate at pH 6.6 were used. A first step in the mechanism of alloy deposition is proposed. This step takes into account the formation of molybdenum(iv) oxides over which Co-Mo alloy may be only deposited if sufficient potential is applied. Co-Mo electrodeposition occurs through an early stage involving low reduction current, related to the formation of molybdenum oxides, followed by a later stage in which the reduction current suddenly increases, corresponding to alloy codeposition. When a low potential is applied, a continuous coloured molybdenum oxide film is formed on the electrode and Co-Mo is not deposited. To induce the alloy deposition on the `oxide film' it is necessary to apply more negative potentials than a threshold value, which depends on the composition of the electrolytic bath. By increasing molybdate concentration in solution, the `threshold potential' shifts to more negative values. intermediate molybdenum oxides were characterized using scanning electron microscopy (SEM), compositional analysis, Raman measurements and Auger and X-ray photoelectron spectroscopies.
- Subjects
MOLYBDENUM oxides; TRANSITION metal oxides; TRANSITION metals; CHROMIUM group; ELECTROFORMING; ALKALI metals
- Publication
Journal of Applied Electrochemistry, 2003, Vol 33, Issue 3/4, p245
- ISSN
0021-891X
- Publication type
Article
- DOI
10.1023/a:1024136909641