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

本研究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，发现超纯离子液体中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-甲基吡咯烷双（三氟甲基磺酰基）酰亚胺，[BMP]TFSI，在薄至1 μ m厚的层作为结晶相。一个副反应，这是尚未理解的，是钽的电沉积可以伴随着显着数量的非化学计量的钽次卤化物。我们假设离子液体的阳离子在难熔金属的电沉积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）酰亚胺，[EMIm]TFSI，薄的非化学计量的钛次卤化物通过电还原的TiCl 4和TiF 4，[BMP]TFSI抑制沉积到这样的程度，它只能通过原位扫描隧道显微镜（STM）在纳米尺度上探测。甚至在[BMP]TFSI和[EMIm]TFSI的混合物中也观察到这种效果。在这个项目中，我们的目的是研究与在原位STM和电化学石英晶体微天平（EQCM）的电沉积钒，铌和钽在[BMP]TFSI，[EMIm]TFSI和它们的混合物。利用STM，我们希望了解离子液体如何影响纳米尺度上电沉积的初始状态。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的信息。

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.