Electrochemical Deposition of Tantalum from Ionic Liquids

Abstract

Tantalum belongs to a class of metals called refractory metals (Niobium, Molybdenum, Tantalum, Tungsten and Rhenium) which are exceptionally resistant to heat and mechanical wear. Due to their tendency to form stable and dense oxide layers, these metals also possess a high resistance towards chemically agressive media. Therefore these metals can be used as protective coatings to build corrosion resistant parts, such as thermowells and valve bodies or for the production of special vacuum furnace components.[1] The electrochemical deposition of refractory metals is a cost-efficient method to coat materials of complex geometries. The negative reduction potential of Ta makes it impossible to use aqueous solutions. Thus ionic liquids (ILs), with an electrochemical window of 5 to 6 V, are promising alternative solvents and have been intensively used in different research fields of electrochemistry during the last years.[2] We have investigated the electrodeposition of Ta using different Ta halides (TaX5, X=F, Cl or Br) and different pyrrolidinium based ILs (1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [BMP][TFSI] and 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate, [BMP][OTf]). We could show that the combination of the precursor and the IL has a strong influence on the electrodeposition process of Ta. Furthermore using IR spectroscopy we found significant differences in the spectra of the different electrolytes which we correlated with results from computated spectra using Density Functional Theory (DFT). The aim of this combined IR/DFT approach is to identify the formed species in our electrolytes. We will present these data together with experimental results from investigations on the reduction mechanism using different electrochemical in-situ techniques (Differential Pulse Voltammetry, Rotating Ring Disk Electrode, Electrochemical Quartz Micro Balance) to show the influence of precursor-IL interaction on the electrodeposition process of Ta from ILs. Literature 1 F. Endres, A.P. Abbott, D. MacFarlane, Electrodeposition from Ionic Liquids, Wiley-VCH, Weinheim, 2008. 2 A. Ispas, B. Adolphi, A. Bund, F. Endres, Phys. Chem. Chem. Phys., 12 (2010) 1793-1803.