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

在本研究项目中，选择了空气和水稳定的离子液体来研究难熔金属钒、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，在1-丁基-1-甲基吡咯烷双(三氟甲基-磺酰基)亚胺([BMP]TFSI)中，钽可以作为晶相在1？m厚的薄层中电沉积。一个尚未被了解的副作用是，在电沉积钽的过程中，可能会伴随着大量的非化学计量比的次卤化物。我们认为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)亚胺([EMIM]TFSI)中，TiCl4和TiF4通过电还原获得了薄的非化学计量比的亚卤化钛，而[BMP]TFSI抑制了沉积，以至于只能在纳米尺度上用原位扫描隧道显微镜(STM)来探测。即使在[BMP]TFSI和[EMIM]TFSI的混合物中也能观察到这种效应。在本项目中，我们用原位扫描隧道显微镜和电化学石英晶体微天平(EQCM)研究了钒、铌和钽在[BMP]TFSI、[EMIM]TFSI及其混合物中的电沉积。通过扫描隧道显微镜，我们想了解离子液体如何影响纳米尺度上电沉积的初始状态。EQCM测量应揭示有关电沉积过程中界面的流变性和摩擦学性质以及所涉及物种的摩尔质量的信息。

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.