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类似的方式才能成功：绿色能源与蓝水相遇。为了可持续的未来，必须开发节能水处理的新技术。电化学方法，如电容去离子（CDI），通过使用带电的碳电极离子电吸附成为可能，是特别感兴趣的。然而，由于浓度依赖的过电选择性，CDI仅限于非常低的离子浓度（微淡水），并且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海水，例如那些能够嵌入的材料（法拉第去离子化：FDI）。典型的FDI材料是具有阳离子插层能力的金属氧化物。FDI也适用于高盐浓度（海水），并且由于更高的电荷存储能力，也使更高的脱盐能力成为可能。然而，金属氧化物中较慢的离子扩散限制了FDI系统的脱盐速率。CDI和FDI的共同之处在于，待脱盐的水介质流经两个电极。除拟电容式海水淡化外，海水淡化电池技术是两种FDI机制之一。在脱盐电池中，离子在特定的插入电位下被固定。在假电容器的情况下，在每个应用电位下都可以连续地结合离子。类似电池的工艺，更容易受到扩散限制，可以潜在地允许离子种类的高选择性。相比之下，更快的伪容量过程可以更少的选择性。作为晶体结构的函数，这两种过程之间的转变尚未得到详细的解决。也不知道在材料老化过程中离子选择性如何变化。因此，了解海水淡化能力、速率、能源效率和离子选择性如何变化是非常有趣的。这是因为离子选择性和高性能海水淡化技术对于原材料的回收，污染物的去除和饮用水供应的清洁水的产生以及通过电解生产氢具有重要意义。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）。为了做到这一点，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，我们还将记录半电池和满电池的电化学反应，并进行低离子浓度和高离子浓度的海水淡化实验。详细介绍了电极老化、离子固定机理、脱盐性能参数和离子选择性。

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.