Institute for Applied Materials─Energy Storage Systems (IAM-ESS), Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen D-76344, Germany.
Helmholtz Institute Ulm for Electrochemical Energy Storage (HIU), Ulm 89081, Germany.
ACS Appl Mater Interfaces. 2023 Jun 14;15(23):28332-28348. doi: 10.1021/acsami.3c01671. Epub 2023 May 30.
The realization of the broad range of application of MXenes relies on the successful and reproducible synthesis of quality materials of tailored properties. To date, most MXenes have been produced making use of acid-based etching methods, yet an in-depth understanding of etching processes is lacking. Herein, we have engaged in a comprehensive study of the multiple variables involved in the synthesis of VCT with focus on the properties of etched materials. Two main sets of experiments were considered, each using a different VAlC precursor and a range of synthesis variables including reaction time and temperature, mixing rate, and type of acid. Correlations of synthesis conditions-materials properties were investigated using a broad range of characterization techniques including analytical methods, scanning and transmission electron microscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Findings indicated the crucial relevance of properties of the MAX precursor such as elemental composition, particle size, and crystal structure on etching processes and properties of etched materials. Particularly, depending on the MAX precursor, two etching patterns were identified, core-shell and plate-by-plate, the latter describing a more efficient etching. Combined studies of elemental composition, crystal structure, and yield quantification allowed us to evaluate the effectiveness of etching processes. XRD studies revealed key crystal-structure-type of acid correlations showing advantages of using a HF/HCl mix over only HF. Analytical methods XRD and XPS delivered insights into undergoing chemical processes and their influence on bulk and surface chemistry of etched materials. The relevance for reaction kinetics of highly correlated variables such as reaction vessel dimensions, mixing efficiency, and reaction temperature was recognized. For the first time, a MXene synthesis has been investigated comprehensively highlighting its multivariable nature and the high variable intercorrelation, opening up venues for further investigation on MAX and MXene synthesis.
MXenes 的广泛应用依赖于成功且可重复地合成具有定制性能的高质量材料。迄今为止，大多数 MXenes 都是通过基于酸的蚀刻方法来制备的，但对于蚀刻过程的深入理解还很缺乏。在此，我们对 VCT 的合成中涉及的多个变量进行了全面研究，重点研究了蚀刻材料的性能。考虑了两组主要的实验，每组实验都使用了不同的 VAlC 前体和一系列合成变量，包括反应时间和温度、混合速率以及酸的类型。使用多种表征技术，包括分析方法、扫描和透射电子显微镜、X 射线衍射（XRD）和 X 射线光电子能谱（XPS），研究了合成条件-材料性能之间的相关性。研究结果表明，MAX 前体的性质，如元素组成、颗粒大小和晶体结构，对蚀刻过程和蚀刻材料的性质具有至关重要的相关性。特别是，根据 MAX 前体的不同，可以识别出两种蚀刻模式，即核壳和逐板，后者描述了一种更有效的蚀刻。对元素组成、晶体结构和产率定量的综合研究，使我们能够评估蚀刻过程的有效性。XRD 研究揭示了关键的晶体结构-酸相关性，表明使用 HF/HCl 混合物比仅使用 HF 更有优势。分析方法 XRD 和 XPS 提供了对正在进行的化学过程及其对蚀刻材料体相和表面化学的影响的深入了解。还认识到了与反应动力学高度相关的变量（如反应容器尺寸、混合效率和反应温度）的相关性。首次对 MXene 合成进行了全面研究，突出了其多变量性质和高度的变量相关性，为进一步研究 MAX 和 MXene 的合成开辟了途径。
