The electrodeposition of transition metals from low-temperature molten salts and nonaqueous solvents
The electrodeposition of transition metals from low-temperature molten salts and nonaqueous solvents
The electrodeposition of a number of first and second-row transition metals has been extensively investigated from both low-temperature molten salts and organic solvents. In fused alkali metal thiocyanates, the coordinated SCN- ligand is activated towards reduction by the presence of the transition metal ion and highlights one of the problems of using compound melts as solvents for metal deposition. In the case of the oxide-fluxing alkali metal pyrosulphates, thermal instability is observed in the molten state and at least one of the decomposition products are electroactive. Thus these melts are unsuitable for electroplating. A range of protic and aprotic amides has been studied as these compounds are representative of polar organic solvents. The protic amides have a limited potentail window and offer no advantages over aqueous electrolytes in electrodeposition. The aprotic amides, DMA and DMF, in the free state, are electrochemically very stable. The species ultimately formed when transition metal halides are dissolved in these solvents are difficult to reduce. Also, it would appear that in the coordinated state amide ligands are subject to similar instabilities as those exhibited by the thiocyanate ligand, and the electron density and LUMO changes induced by coordination render the amide more susceptible to oxygen abstraction reactions. For these reasons it is argued that the amides and similar types of polar solvent are ill-suited for transition metal deposition. The chemical and electrochemical stability of aromatic hydrocarbons are amongst the highest known for organic compounds, and little interaction with transition metal solutes is to be expected. It has been demonstrated that transition metal ions can be dissolved in very high concentrations (>char621M) in aromatic hydrocarbons provided that part of their coordination sphere contains a hydrocarbon chain such as a propyl or butyl group. Simple coordination compounds of the type [Amine_5Cr(III)Cl].Cl_2 are electroactive in mono or polyaromatic hydrocarbons containing TBABF_4 as a supporting electrolyte. Cr(III) can be reduced to the metallic state - the first time this has been achieved from a nonaqueous solvent. It is proposed that the aromatic hydrocarbons are sufficiently stable to be used for the electrodeposition of a wide range of transition metals. (D72865/87)
University of Southampton
1986
Potter, Robert John
(1986)
The electrodeposition of transition metals from low-temperature molten salts and nonaqueous solvents.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
The electrodeposition of a number of first and second-row transition metals has been extensively investigated from both low-temperature molten salts and organic solvents. In fused alkali metal thiocyanates, the coordinated SCN- ligand is activated towards reduction by the presence of the transition metal ion and highlights one of the problems of using compound melts as solvents for metal deposition. In the case of the oxide-fluxing alkali metal pyrosulphates, thermal instability is observed in the molten state and at least one of the decomposition products are electroactive. Thus these melts are unsuitable for electroplating. A range of protic and aprotic amides has been studied as these compounds are representative of polar organic solvents. The protic amides have a limited potentail window and offer no advantages over aqueous electrolytes in electrodeposition. The aprotic amides, DMA and DMF, in the free state, are electrochemically very stable. The species ultimately formed when transition metal halides are dissolved in these solvents are difficult to reduce. Also, it would appear that in the coordinated state amide ligands are subject to similar instabilities as those exhibited by the thiocyanate ligand, and the electron density and LUMO changes induced by coordination render the amide more susceptible to oxygen abstraction reactions. For these reasons it is argued that the amides and similar types of polar solvent are ill-suited for transition metal deposition. The chemical and electrochemical stability of aromatic hydrocarbons are amongst the highest known for organic compounds, and little interaction with transition metal solutes is to be expected. It has been demonstrated that transition metal ions can be dissolved in very high concentrations (>char621M) in aromatic hydrocarbons provided that part of their coordination sphere contains a hydrocarbon chain such as a propyl or butyl group. Simple coordination compounds of the type [Amine_5Cr(III)Cl].Cl_2 are electroactive in mono or polyaromatic hydrocarbons containing TBABF_4 as a supporting electrolyte. Cr(III) can be reduced to the metallic state - the first time this has been achieved from a nonaqueous solvent. It is proposed that the aromatic hydrocarbons are sufficiently stable to be used for the electrodeposition of a wide range of transition metals. (D72865/87)
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Published date: 1986
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Local EPrints ID: 460870
URI: http://eprints.soton.ac.uk/id/eprint/460870
PURE UUID: 2db90bbe-4b7b-4909-9fd1-51e74dc6dee9
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Date deposited: 04 Jul 2022 18:31
Last modified: 04 Jul 2022 18:31
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Author:
Robert John Potter
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