Ti_n+1C_n MXenes with fully saturated and thermally stable Cl terminations

Abstract

MXenes are a rapidly growing family of 2D materials that exhibit a highly versatile structure and composition, allowing for significant tuning of the material properties. These properties are, however, ultimately limited by the surface terminations, which are typically a mixture of species, including F and O that are inherent to the MXene processing. Other and robust terminations are lacking. Here, we apply high-resolution scanning transmission electron microscopy (STEM), corresponding image simulations and first-principles calculations to investigate the surface terminations on MXenes synthesized from MAX phases through Lewis acidic melts. The results show that atomic Cl terminates the synthesized MXenes, with mere residual presence of other termination species. Furthermore, in situ STEM-electron energy loss spectroscopy (EELS) heating experiments show that the Cl terminations are stable up to 750 °C. Thus, we present an attractive new termination that widely expands the MXenes' functionalization space and enable new applications.

Element Replacement Approach by Reaction with Lewis Acidic Molten Salts to Synthesize Nanolaminated MAX Phases and MXenes

“…1d to O-containing terminals. 40 Thus, a small part of Cl terminations might be replaced by O-containing terminals during the producing process like water washing, which could also contribute to the oxygen element detected on the surface. In addition, large Zn spheres can also be observed in the product, which can be easily distinguished from the MXenes (Fig.…”

“…Note that the Ti3C2Cl2 MXenes show good ordering along the basal planes, which is in agreement with the intense (000l) peaks in the XRD patterns. For a more detailed investigation on the Cl terminations, please see ref40 40.…”

Are MXenes suitable as cathode materials for rechargeable Mg batteries?

“…69 Nevertheless, the viable energy densities of V2CO2 depends on uniformly terminated V2CO2, which pose a crucial challenge. Recent work on fluorine-free synthesis of Ti3C2Tx gives some promise, [70][71][72][73][74] but a similar synthesis approach may not be feasible for V2CO2 given the much harsher etching conditions required for V2CTx, indicative of substantially stronger metal-aluminium bonds. 75 Furthermore, the prerequisite of having Mg 2+ successfully desolvating from the electrolyte and entering the interlayers still remains.…”

How Much Oxygen Can a MXene Surface Take Before It Breaks?

“…[24] Recently, Cl was added to the list of terminations and was demonstrated as an exclusive termination. [25] Previous efforts have shown that it is possible to vary the amount of F and O through the etchant, [16] while keeping the overall number of terminations constant. Exclusive termination by O (M n+1 X n O 2 ) was predicted by theoretical means to improve the volumetric capacity of supercapacitors, [26,27] and the catalytic efficiency in HER applications.…”