Electroreduction of tantalum fluoride in a room temperature ionic liquid at variable temperatures

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Abstract
The present paper deals with the electroreduction of TaF5 in the room temperature ionic liquid 1-butyl-1-methyl-pyrrolidinium bis(tri-fluoromethylsulfonyl)imide ([BMP]Tf2N) at different temperatures for the sake of electrodeposition of tantalum. The study was carried out using cyclic voltammetry and chronoamperometry measurements complemented by SEM-EDAX and XRD investigations. In situ scanning tunneling microscopy and I–U tunneling spectroscopy were also utilized for characterization of the electrodeposits. The results show that, in addition to the formation of insoluble compounds, Ta can be electrodeposited in the ionic liquid ([BMP]Tf2N) containing 0.5 M TaF5 at 200 °C on polycrystalline Pt and Au(111) electrodes. By addition of LiF to the electrolyte, the quality and the adherence of the electrodeposit were found to be improved. An in situI–U tunneling spectrum with about 300 nm thickness of the electrodeposit shows metallic behaviour indicating the formation of elemental tantalum. Moreover, the XRD patterns of the electrodeposit, obtained potentiostatically at −1.8 V (vs. Pt) in ([BMP]Tf2N) containing 0.25 M TaF5 and 0.25 M LiF on Pt electrode at 200 °C, show the characteristic patterns of crystalline tantalum.