Narrow gap flow electrolysis cells and the challenge of hydrogen bubbles – a combined approach via modelling and experiment

为了以后在技术规模上应用电解转化，电解的施加电压必须低以确保高能量效率。解决这个问题的一个概念是在阳极和阴极表面之间采用小距离。已经发现这种窄间隙允许使用导电性较低的介质。通常，较少的离子也引起较小的电压降。这是特别重要的，因为电解质的下游处理由于较低的盐负载而被简化。在计划的项目中，建模将用于研究低盐浓度或无盐条件下薄膜的导电机制。我们将重点讨论电场的作用-即使施加的电压很小，薄膜中的电场也可能很大-对于介质的分子结构，无论是在体还是靠近电极表面。此外，我们将研究电场对介质的动力学和粘度的影响，以阐明在粘度问题和传质对电解产生不利影响之前，这种细胞可以变得多么薄。 研究网络中的第二个挑战是使用流动电解池时分子氢的形成。这种阴极反应在该框架内是期望的，但是具有未分隔的池几何形状的流动池可能由于其增加的体积而被大气泡阻塞。因此，这种电池的效率受到很大限制。在这方面，正在采取两种办法来控制这一普遍问题。一方面，要使用支持表面活性剂，其限制气泡的尺寸并产生至少一种泡沫，该泡沫仍然是导电的并继续支持电解。或者，也将测试发散电极布置。这一部分也将得到建模研究的支持。另一种方法是在载体结构上使用非常薄的钯箔来去除阴极后面的氢，而不影响所需电解的窄间隙。

For a later application of electrolytic conversions on a technical scale, the applied voltage for the electrolysis has to be low to ensure a high energy efficiency. One concept to tackle this is to employ a small distance between anode and cathode surface. Such narrow gaps have been found to allow the use of less conductive media. Usually, fewer ions also induce a smaller voltage drop. This is particularly important, because the downstream processing of the electrolytes is simplified due to a lower salt load. Within the planned project, modeling will be used to investigate the mechanisms of conductivity in thin films at low salt concentration or in the absence of salt. We will focus on the role of the electric field – which can be large in thin films even if the applied voltage is small - for the molecular structure of the medium, both in the bulk and close to the electrode surfaces. Furthermore, we will investigate the effect of electric fields on the dynamics and the viscosity of the medium, in order to elucidate how thin such cells can become before viscosity problems and mass transport adversely affect electrolysis. A second challenge within the research network is the formation of molecular hydrogen when using flow electrolysis cells. This cathodic reaction is desired within this framework, but flow cells with undivided cell geometry, can be blocked by large gas bubbles due to their increased volume. Thus, the efficiency of such cells is greatly limited. Here, two approaches are being pursued in order to get this general problem under control. On the one hand, supporting surfactants are to be used which limit the size of the gas bubbles and produce at least a foam which is still conductive and continues to support electrolysis. Alternatively, divergent electrode arrangements will be tested as well. This part will also be supported by modeling studies. An alternative way will be to use very thin palladium foils on carrier structures to remove the hydrogen behind the cathode, without affecting narrow gap for the desired electrolysis.