Investigations on the electrochemistry and reactivity of tantalum species in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide using X-ray photoelectron spectroscopy (in situ and ex-situ XPS)

Abstract

Tantalum is a metal whose properties enable it to be used in a wide range of technological applications. In the present work, the underlying electrochemical processes of tantalum species in ionic liquids (ILs) are investigated using in situ X-ray photoelectron spectroscopy (XPS) in ultra-high vacuum. For this purpose electrochemical deposition of tantalum on a gold wire from 0.1 mol/L TaF5 in a 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py1,4]TFSI) electrolyte was studied by in situ electrochemical XPS. The cyclic voltammogram shows two reduction peaks and one oxidation peak, indicating a complex electrochemical behaviour. The electrochemical in situ XPS gives evidence of a reduction reaction, although no metallic tantalum could be detected on the gold wire. In order to investigate the reactivity of tantalum in more detail, thin IL films were prepared on tantalum by physical vapor deposition and these were examined by XPS. Decomposition reactions were observed with the formation of subhalides, oxyfluorides, or tantalum sulfides, showing the decomposition of the ionic liquid. The decomposition products indicate the splitting of the C-F bond of the TFSI anion.