On the Electrodeposition of Niobium from 1-Butyl-1-Methylpyrrolidinium Bis(trifluoromethylsulfonyl)imide at Conductive Diamond Substrates

Abstract

This work relates to the electrochemical deposition of Nb from a liquid solution in which the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMP][TFSA]) is used as solvent. Conductive diamond was employed as substrate, while the experiments were carried out with NbF5 in the presence of either NaF or LiF. Cyclic voltammetries were used to characterise the electrochemical behaviour of the system. Deposition experiments were carried out at fixed potentials, corresponding to the voltammetric peaks of the cathodic scans. The surfaces were characterised by scanning electron microscope-energy dispersive X-ray (SEM-EDX) analysis and the results used in combination with the voltammetries to establish a possible mechanism for the Nb electrodeposition process. The electroreduction of Nb(V) to Nb(0) was found to proceed through different steps, involving the formation of the Nb(II) carbide and other nonstoichiometric carbide phases. The effect of Na and Li ions on the electrochemical process was studied: although three voltammetric peaks were detected in both cases, an appreciable depolarisation of the cathodic reactions was observed in the presence of Li ions. XRD analysis confirmed that a coating of metallic Nb was obtained at −1.5 V and 125 °C in the presence of LiF.