Hydrothermal synthesis of metal carbide-derived metal oxide nanoparticles for electrochemical energy storage (electro-MOXen)

该项目的重点是开发用于电化学应用的金属碳化物衍生的金属氧化物纳米颗粒。取决于合成参数，将获得具有残余碳化物或碳组分的金属氧化物颗粒或纳米杂化物。合成开始于三元金属碳化物（MAX相）的产生，其可以分层为二维碳化物（MXene）。后者可以（完全）氧化成金属氧化物纳米颗粒或（部分）氧化形成金属氧化物/碳化物（或碳）混合物。MAX相属于一大组层状三元金属碳化物、碳氮化物和氮化物，化学组成为Mn+1AXn。M是过渡金属，A是第13和14族元素，X是碳或氮。M层由A原子连接，X原子填充M八面体的差距。选择性蚀刻A原子HF处理产生二维金属碳化物（M-X层）。这种材料被称为MXene，并显示出有趣的机械，电气和电化学特性。随后氧化层离的MXene形成金属氧化物纳米颗粒或与碳或碳化物的混合物，这取决于合成条件。我们已经合成了不同类型的MAX相，包括Ti 3AlC 2和Ti 3SiC 2。使用化学处理，实现A原子的蚀刻，从而产生层状金属碳化物（MXene）。在初步工作中，我们已经证明了调整氧化的Ti 3C 2（MXen），形成二氧化钛层（MOXen），使用短期的热退火在合成空气中在高温下。然而，仍然存在几个未解决的问题，以实现用于电池或超级电容器的高纯度和可再生的MOXene。在该项目中，MOXenes及其与碳或碳化物的混合物将使用211-MAX相开发。我们将改变M原子（V2 AlC，Ti 2AlC，Nb 2AlC），并研究具有混合M原子占据的MAX相（（Ti，Nb）2AlC，（Ti，V）2AlC）。MAX到MXene的分层将仅通过HF处理和使用水热反应煅烧成金属氧化物来进行。根据合成条件，可以产生纯金属氧化物纳米颗粒或金属氧化物/碳化物（或碳）纳米杂化物。后者的混合物是特别感兴趣的电化学应用，由于其高的固有电导率，除了电化学活性材料（金属氧化物）。将对所有MOXene材料进行严格的电化学基准测试。所有电化学测量将在使用有机电解质的不对称混合电池中进行。表征的重点是锂和钠的嵌入与国家的最先进的表征技术，以调查比能量，功率和性能稳定性。原位方法将补充我们对能量储存过程的机械理解。

This project focuses on the development of metal carbide-derived metal oxide nanoparticles for electrochemical applications. Depending on the synthesis parameters, metal oxide particles or nanohybrids with residual carbide or carbon component will be obtained. The synthesis starts with the production of a ternary metal carbide (MAX phase), which can be delaminated to two-dimensional carbides (MXenes). The latter can be (fully) oxidized to metal oxide nanoparticles or (partially) oxidized to form a metal oxide / carbide (or carbon) hybrids. MAX-phases belong to a large group of laminated, ternary metal carbides, carbonitrides, and nitrides with the chemical composition Mn+1AXn. M is a transition metal, A an element of group 13 and 14 and X carbon or nitrogen. The M-layers are connected by the A-atoms and the X-atoms fill the gap of the M-octahedra. Selective etching of A-atoms HF treatment yields two-dimensional metal carbides (M-X layers). This material is called MXene and displays interesting mechanical, electrical and electrochemical properties. Subsequent oxidation of the delaminated MXenes forms metal oxide nanoparticles or hybrids with carbon or carbide dependent on the synthesis conditions.Different types of MAX phases were already synthesized by us including Ti3AlC2 und Ti3SiC2. Using chemical treatment, etching of A-atoms is achieved, resulting in layered metal carbides (MXenes). In preliminary work, we have demonstrated adjusted oxidation of Ti3C2 (MXen) to form TiO2-layers (MOXen) using short-term thermal annealing in synthetic air at high temperatures. However, there are still several unresolved issues to achieve high purity and reproducible MOXenes for usage in batteries or supercapacitors. In this project, MOXenes and their hybrids with carbon or carbide will be developed using 211-MAX-phases. We will vary the M-atom (V2AlC, Ti2AlC, Nb2AlC) and also investigate MAX-phases with mixed M-atom occupancy ((Ti,Nb)2AlC, (Ti,V)2AlC). The delamination of MAX to MXene will be exclusively performed by HF treatment and the calcination to metal oxide by using hydrothermal reactions. Dependent on the synthesis conditions, pure metal oxide nanoparticles can be generated or metal oxide / carbide (or carbon) nanohybrids. The latter hybrids are especially interesting for electrochemical applications due to their high intrinsic electrical conductivity in addition to the electrochemically active material (metal oxide). Rigorous electrochemical benchmarking will be carried out for all MOXene materials. All electrochemical measurements will be performed in asymmetric hybrid cells using organic electrolyte. The characterization focuses on lithium and sodium intercalation with state-of-the-art characterization techniques to investigate the specific energy, power, and performance stability. In situ methods will complement our mechanistic understanding of the energy storage processes.