MXenes constitute a rather recent addition to two-dimensional materials, which exhibit a large range of tunable properties . These materials can be synthesized in both bulk form as well as thin film structures. Although many of their properties remain unexplored they exhibit outstanding properties for applications in electrochemical energy storage devices, EESDs .
MXenes originate from a large family of naturally nanolaminated materials known as MAX phases, where M is a transition metal, A a group A element and X is either C or N, following the general formula Mn+1AXn., see e.g. the schematic in fig. 1a. Upon chemical etching, the A element leaves the MAX phase and results in single sheets, with surfaces functionalized, Tx, by O, OH and F to give the MXene formula Mn+1XnTx . Bulk made MXene hence exhibit an extremely large surface area per volume, and are consequently attractive for energy storage. The material is easily intercalated and delaminated using standard methods.
To date, shy of 20 different 2D structures in this family has been synthesized and the wide range of choice of e.g. M elements enable a formidable playground for materials engineering. Among the more interesting structures synthesized to date, are those which are achieved while alloying different M elements to achieve (M1,M2)n+1Xn, see e.g. . Through theoretical predictions and subsequent materials synthesis, we have been able to tune the material to exhibit out of-plane ordering as well as in-plane ordering, by means of repetitively alternating M elements. Additionally, by choosing the M elements carefully, we can incorporate those which are loosely bound and prone to chemical etching. This further enable a reduced MXene structure exhibiting in-plane vacancy ordering. The process is shown in fig. 1, where a MAX phase of 2M elements is schematically etched to produce the reduced, in-plane vacancy ordered structure as seen in cross-section (fig 1b) and plan-view (fig 1c). The corresponding synthesized structure is shown by HRSTEM methods in fig 2. These new MXenes additionally enable further tuning by vacancy ripening. Upon irradiating and heating the sample, the vacancies ripen to produce 2D sheets with a mesoporous structure, which exhibits a significant application in filtering and for enhancing ion mobilities in EESD applications.
This presentation will highlight the research front in this new family of materials, and present the opportunities given through its vast tailoring ability. Electron microscopy, and in particular aberration corrected STEM in combination with EELS and EDS has proven critical in the exploration of these new materials.
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To cite this abstract:Per Persson; Exploring and Tailoring Structural Properties of the Two-Dimensional Family ofMXenes. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/exploring-and-tailoring-structural-properties-of-the-two-dimensional-family-ofmxenes/. Accessed: December 12, 2018
EMC Abstracts - https://emc-proceedings.com/abstract/exploring-and-tailoring-structural-properties-of-the-two-dimensional-family-ofmxenes/