The electrochemical reduction of 0.1 M TaF5 in two hydrophobic ionic liquids (1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate ([Py-1,Py-4] FAP) and 1-butyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl) amide ([Py-1,Py-4] TFSA) is probed using three in situ techniques: scanning tunneling microscopy (STM), atomic force microscopy (AFM), and electrochemical quartz crystal microbalance (EQCM). These techniques reveal that under similar conditions TaF5 is more easily reduced in the liquids with [TFSA] than [FAP] anions. Increasing the temperature reduced the viscosity and density of the ionic liquids which facilitates TaF5 electroreduction, in particular, in [Py-1,Py-4] TFSA. A herringbone reconstruction of the Au electrode was observed by STM for both ionic liquids with and without TaF5. Ta deposition was proved by STM and EQCM in [Py-1,Py-4] TFSA. Cracked layers, with ionic liquid trapped inside, were obtained by direct plating from the [TFSA] ionic liquid. No Ta containing deposits could be obtained in the liquid with the [FAP] anion. (C) 2015 Elsevier Ltd. All rights reserved.