Study of rhodium deposition reaction from chlorine and sulphate solutions
Study of rhodium deposition reaction from chlorine and sulphate solutions
The electrodeposition of rhodium metal onto vitreous carbon and copper from solutions of Rh(III) in aqueous chloride at pH 1.5 - 4.0 and aqueous sulphate, pH ≈ 3.3 has been investigated. Cyclic voltammetry, rotating disc electrodes and potential step experiments have been used to probe the mechanism and kinetics of these reactions. The current efficiency for electrodeposition has been determined and the quality of the electroplates has been examined by scanning electron microscopy and other techniques.
Rh(III) complexes are known to be substitution inert and UV-visible spectroscopy as well as 103Rh NMR confirmed that, in both chloride and sulphate media, the Rh(III) exist as a mixture of several complexes which do not interchange even on a timescale of days. The voltammetry of such a solution would be expected to show several waves/peaks; in fact, the voltammetry was very simple and all the Rh(III) species reduced directly in a single process which became mass transport controlled beyond the peak/wave. The electrochemistry is difficult to interpret in a way which is compatible with the beliefs of inorganic chemists but some tentative explanations are discussed.
The early stages of Rh nucleation and growth have been studied. The overpotentials associated with nucleation and electron transfer have been established and it was shown that in all solutions, the deposit was formed by progressive nucleation and three dimensional growth of the nuclei under electron transfer control. After overlap of these centres, further growth occurs under planar diffusion control. Both H+ and H2O reduction are catalysed by the freshly plated Rh but the importance of both processes depends strongly on the pH 3. In addition, the adsorption/desorption of hydrogen atoms processes were observed by voltammetry.
Good quality electroplates are formed on vitreous carbon from either chloride or sulphate media. On copper (and steel) substrates, the deposits were good only from sulphate solutions. In chloride media, the metal substrates corroded and a Rh film was formed by a cementation process. Moreover, even low concentrations of Cl- in the sulphate bath led to a loss of reflectivity and this probably results from roughening of the substrate by slow corrosion.
University of Southampton
Urbina Zárate, Rosa Isabel
1996
Urbina Zárate, Rosa Isabel
Urbina Zárate, Rosa Isabel
(1996)
Study of rhodium deposition reaction from chlorine and sulphate solutions.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
The electrodeposition of rhodium metal onto vitreous carbon and copper from solutions of Rh(III) in aqueous chloride at pH 1.5 - 4.0 and aqueous sulphate, pH ≈ 3.3 has been investigated. Cyclic voltammetry, rotating disc electrodes and potential step experiments have been used to probe the mechanism and kinetics of these reactions. The current efficiency for electrodeposition has been determined and the quality of the electroplates has been examined by scanning electron microscopy and other techniques.
Rh(III) complexes are known to be substitution inert and UV-visible spectroscopy as well as 103Rh NMR confirmed that, in both chloride and sulphate media, the Rh(III) exist as a mixture of several complexes which do not interchange even on a timescale of days. The voltammetry of such a solution would be expected to show several waves/peaks; in fact, the voltammetry was very simple and all the Rh(III) species reduced directly in a single process which became mass transport controlled beyond the peak/wave. The electrochemistry is difficult to interpret in a way which is compatible with the beliefs of inorganic chemists but some tentative explanations are discussed.
The early stages of Rh nucleation and growth have been studied. The overpotentials associated with nucleation and electron transfer have been established and it was shown that in all solutions, the deposit was formed by progressive nucleation and three dimensional growth of the nuclei under electron transfer control. After overlap of these centres, further growth occurs under planar diffusion control. Both H+ and H2O reduction are catalysed by the freshly plated Rh but the importance of both processes depends strongly on the pH 3. In addition, the adsorption/desorption of hydrogen atoms processes were observed by voltammetry.
Good quality electroplates are formed on vitreous carbon from either chloride or sulphate media. On copper (and steel) substrates, the deposits were good only from sulphate solutions. In chloride media, the metal substrates corroded and a Rh film was formed by a cementation process. Moreover, even low concentrations of Cl- in the sulphate bath led to a loss of reflectivity and this probably results from roughening of the substrate by slow corrosion.
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Published date: 1996
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Local EPrints ID: 459367
URI: http://eprints.soton.ac.uk/id/eprint/459367
PURE UUID: 3078b863-06c7-4f2b-a4b2-8f7603ad5d6c
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Date deposited: 04 Jul 2022 17:09
Last modified: 04 Jul 2022 17:09
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Author:
Rosa Isabel Urbina Zárate
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