Studying the transition from pseudocapacitive to battery-like desalination for ion selectivity (SELECT)

能源转型只有通过与水转型的类比才能成功：绿色能源与蓝色水相遇。为了可持续的未来，必须开发新的节能水处理技术。电容去离子(CDI)等电化学方法尤其令人感兴趣，这种方法是通过使用带电的碳电极进行离子电吸附而实现的。然而，由于依赖于浓度的渗透选择性，CDI被限制在非常低的离子浓度(微咸水)，并取决于电极材料的比表面积。也可以通过装载法拉第材料来淡化水，例如那些能够插入的材料(法拉第去离子：FDI)。典型的外国直接投资材料是能够插入阳离子的金属氧化物。外国直接投资也适用于高盐浓度(海水)，由于更高的电荷存储能力，也可以实现更高的海水淡化能力。然而，金属氧化物中的离子扩散速度较慢，限制了外国直接投资系统的海水淡化速度。CDI和FDI的共同点是待淡化的水介质流经两个电极。除伪电容淡化外，电池淡化技术是两种FDI机制之一。在海水淡化电池中，离子被固定在特定的嵌入电位上。在赝电容器的情况下，在每个施加的电势下都可以连续地掺入离子。类似电池的过程更容易受到扩散限制，可能会对一种离子物种具有很高的选择性。相比之下，较快的假容量过程可能不那么有选择性。作为晶体结构的函数，这两个过程之间的转变尚未被详细讨论。离子选择性在材料老化过程中的变化也不是很明显。因此，了解海水淡化能力、脱盐速率、能量效率和离子选择性的变化是非常有意义的。这是因为离子选择性和高性能的海水淡化技术对于回收原材料、去除污染物和产生饮用水供应的清洁水以及通过电解生产氢气非常重要。我们的项目将专门将金属氧化物(氧化钒和氧化钼)应用于具有外表面的碳材料(碳纳米洋葱和碳纳米管)。为此，我们使用了可以在纳米尺度上控制的原子层沉积(ALD)方法。除了全面的材料表征外，我们还将在半电池和全电池中记录电化学，并在低离子浓度和高离子浓度下进行海水淡化实验。详细讨论了电极老化、离子固定机理以及由此产生的脱盐和离子选择性的性能参数。

The energy transition can only succeed through its analog of the water transition: green energy meets blue water. New technologies for energy-efficient water treatment must be developed for a sustainable future. Electrochemical methods such as capacitive deionization (CDI), made possible by ion electrosorption using electrically charged carbon electrodes, are of particular interest. However, due to the concentration-dependent permselectivity, CDI is limited to very low ion concentrations (brackish water) and depends on the specific surface area of the electrode material. It is also possible to desalinate water by loading Faradaic materials, such as those that enable intercalation (Faradaic deionization: FDI). A typical FDI material is metal oxides that are capable of cation intercalation. FDI also works with high salt concentrations (seawater) and, due to the higher charge storage capacity, also enables higher desalination capacities. However, the slower ion diffusion in metal oxides limits the desalination rates of FDI systems. CDI and FDI have in common that the aqueous medium to be desalinated flows past two electrodes.In addition to pseudo-capacitive desalination, the technology of desalination batteries represents one of two FDI mechanisms. In desalination batteries, ions are immobilized at specific intercalation potentials. In the case of pseudocapacitors, incorporating ions is possible continuously at every applied potential. Battery-like processes, which are more subject to diffusion limitations, can potentially allow high selectivity for an ionic species. In contrast, the faster process of pseudocapacity can be less selective. As a function of the crystal structure, the transition between these two processes has not yet been addressed in detail. Neither does how the ion selectivity changes during material aging. Therefore, it is of great interest to know how desalination capacity, rate, energy efficiency, and ion selectivity change. This is because ion-selective and high-performance desalination technologies are of great importance for the recovery of raw materials, the removal of pollutants and the generation of clean water for the drinking water supply, and the production of hydrogen via electrolysis.Our project will specifically apply metal oxides (vanadium oxide and molybdenum oxide) to carbon materials with an outer surface (carbon nano onions and carbon nanotubes). To do this, we use the atomic layer deposition (ALD) method that can be controlled on the nanoscale. In addition to comprehensive material characterization, we will record the electrochemistry in half and full cells and conduct desalination experiments with low and high ion concentrations. The electrode aging, the ion immobilization mechanism, and the resulting performance parameters of desalination and ion selectivity are addressed in detail.