STM and QCM investigation of refractory metal electrodeposition in ionic liquids: influence of the ionic liquid on the electroreduction processes of the respective refractory metal halides

本课题选用空气和水稳定的离子液体，研究难熔金属钒、铌和钽的电沉积。最近我们以铝为例发现，超纯离子液体的阳离子对金属电沉积有很强的影响。我们还可以证明钽可以电沉积在1-丁基-1-甲基吡啶二（三氟甲基磺酰基）亚胺[BMP]TFSI中，厚度可达1¿m。一个尚未了解的副反应是，钽的电沉积可能伴随着大量的非化学计量的钽亚卤化物。我们假设离子液体的阳离子在电沉积难熔金属中起着至关重要的作用，就像铝沉积的情况一样。而在1-乙基-3-甲基咪唑双（三氟甲基磺酰基）亚胺[EMIm]TFSI中，通过电还原TiCl4和TiF4获得了薄的非化学计量的钛亚卤化物，[BMP]TFSI抑制沉积的程度如此之大，以至于只能通过原位扫描隧道显微镜（STM）在纳米尺度上进行探测。即使在[BMP]TFSI和[EMIm]TFSI的混合物中也观察到这种效应。在本项目中，我们旨在利用原位STM和电化学石英晶体微天平（EQCM）研究钒、铌和钽在[BMP]TFSI、[EMIm]TFSI及其混合物中的电沉积。通过STM，我们想了解离子液体如何影响纳米级电沉积的初始状态。EQCM测量应揭示电沉积过程中界面的流变学和摩擦学特性以及相关物质的摩尔质量。

In this research project selected air and water stable ionic liquids shall be employed to investigate the electrodeposition of the refractory metals vanadium, niobium and tantalum. Recently we found at the example of aluminium that the cation of ultra pure ionic liquids has a strong effect on metal electrodeposition. We could also show that tantalum can be electrodeposited in 1-Butyl-1-methylpyrrolidinium bis(trifluoromethyl-sulfonyl)imide, [BMP]TFSI, in thin up to 1 ¿m thick layers as a crystalline phase. A side reaction, which is not yet understood, is that the electrodeposition of tantalum can be accompanied by remarkable amounts of nonstoichiometric tantalum subhalides. We assume that the cation of the ionic liquid plays ¿ as in the case of aluminium deposition ¿ a crucial role in the electrodeposition of refractory metals. Whereas in 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, [EMIm]TFSI, thin non-stoichiometric titanium subhalides are obtained by electroreduction of TiCl4 and TiF4, [BMP]TFSI suppresses deposition to such an extent that it can only be probed by in situ Scanning Tunneling Microscopy (STM) on the nanoscale. Even in mixtures of [BMP]TFSI and [EMIm]TFSI this effect is observed. In this project we aim to investigate with the in situ STM and with the electrochemical quartz crystal microbalance (EQCM) the electrodeposition of vanadium, niobium and tantalum in [BMP]TFSI, [EMIm]TFSI and mixtures of them. With the STM we would like to understand how the ionic liquid influences the initial states of electrodeposition on the nanoscale. EQCM measurements shall reveal information about the rheological and tribological properties of the interface during the electrodeposition processes and the molar masses of the involved species.