Pseudocapacitive deionization with nanolamellar metal carbides (MXene CDI)

电容去离子(CDI)是一种新兴的去除低摩尔浓度(100 mm以下)水介质中离子的高效、低能耗技术。凭借这一优点，CDI特别适用于微咸水或工业水流的去离子。CDI的过程类似于双层电容器(超级电容器)的操作：离子被电吸附到高度多孔的电极表面，并有效地从给水中去除。然后通过放电或电压反转来实现电极的再生。到目前为止，由于纳米多孔碳具有较高的比表面积和较高的化学稳定性，目前在CDI领域的大部分工作都局限于纳米多孔碳的合成、分析和应用。随着对碳的关注，大多数工作已经探索了通过电化学双层离子固定来纯粹的静电去离子。这就是为什么到目前为止，大多数碳作为电容材料被应用于CDI。拟议的项目将首次探索一种用于电容去离子的纯伪电容材料，即MXene。假电容是通过类似电容器的电响应(线性电荷-电压)来区分的，而电荷存储是通过法拉第过程(离子嵌入)来完成的。MXenes是一类新型的二维金属碳化物、碳氮化物和氮化物，于2011年首次被描述。它们是通过对MAX相进行化学处理而得到的，MAX相是三元金属碳化物、碳氮化物和氮化物--一个拥有60多个成员的纳米片层材料的大家族。用HF进行的化学腐蚀选择性地从MAX的A层中去除原子，在结构中只剩下M和X原子。在没有层间A原子的情况下，三维MAX结构被转移到二维纳层MXNE中。申请一个博士生职位的资金将结合材料科学和水电化学应用这两个核心主题。博士生将从最大相V2AlC中优化合成V2C MXene，并对其表面官能团进行化学修饰(氧化/去除表面官能团等)。通过热方法。探讨了结构和表面化学对MXene(修饰前后)在以氯化钠为盐的水介质中电化学行为的影响。除了CDI脱盐能力和脱盐率外，还将研究电化学循环(包括原位方法)过程中的寿命和结构变化，并定性地说明MXene性能与CDI性能之间的关系。

Capacitive deionization (CDI) is an emerging technology, promising high efficiency and low energy consumption for the removal of ions from aqueous media with low molar concentration (below 100 mM). By this virtue, CDI is particularly attractive for deionization of brackish water or industrial water streams. The process of CDI is similar to the operation of double-layer capacitors (supercapacitors): ions are electrosorbed onto the surface of highly porous electrodes and effectively removed from the feed water stream. Regeneration of the electrodes is then accomplished by discharging or voltage reversal. Until now, the majority of works in the field of CDI has been limited to the synthesis, analysis, and application of nanoporous carbon considering the high surface area and relatively high chemical stability. With the focus on carbon, most works have explored purely electrostatic deionization by ion immobilization via electrochemical double layers. This is why mostly carbon as a capacitive material has been applied for CDI so far.The proposed project will, for the first time, explore a purely pseudocapacitive material for capacitive deionization, namely MXene. Pseudocapacitance is distinguished by a capacitor-like electric response (linear charge-vs.-voltage), while charge storage is accomplished by a Faradaic process (ion intercalation). MXenes are a novel class of two-dimensional metal carbides, carbonitrides, and nitrides, first described in 2011. They are derived by chemical treatment of MAX phases, which are ternary metal carbides, carbonitrides, and nitrides - a large family of nanolamellar materials with over 60 members. Chemical etching by HF selectively removes atoms from the A-layer in MAX, leaving only M and X atoms left in the structure. Without the interlayer A-atoms, the three-dimensional MAX structure is transferred to two-dimensional nanolamellar MXene.The requested funding for one PhD student position will combine the two core topics of material science and aqueous electrochemical application. The PhD student will optimize the synthesis of V2C MXene from the MAX phase V2AlC and chemically modify its surface functionalities (oxidation / removal of surface functional groups etc.) by thermal methods. The impact of structure and surface chemistry on the electrochemical behavior of MXene (with / without modification) in aqueous media with NaCl as the salt will be explored. Besides CDI salt removal capacity and desalination rate, the longevity and structural changes during electrochemical cycling (including in situ methods) will be studied and a qualitative statement on the relations between MXene properties and CDI performance will be derived.