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MXenes are a rapidly growing family of 2D transition metal carbides and nitrides that are promising for various applications, including energy storage and conversion, electronics, and healthcare. Hydrofluoric‐acid‐based etchants are typically used for large‐scale and high‐throughput synthesis of MXenes, which also leads to a mixture of surface terminations that impede MXene properties. Herein, a computational thermodynamic model with experimental validation is presented to explore the feasibility of fluorine‐free synthesis of MXenes with uniform surface terminations by dry selective extraction (DSE) from precursor MAX phases using iodine vapors. A range of MXenes and respective precursor compositions are systematically screened using first‐principles calculations to find candidates with high phase stability and low etching energy. A thermodynamic model based on the “CALculation of PHAse Diagrams” (CALPHAD) approach is further demonstrated, using Ti₃C₂I₂as an example, to assess the Gibbs free energy of the DSE reaction and the state of the byproducts as a function of temperature and pressure. Based on the assessment, the optimal synthesis temperature and vapor pressure are predicted and further verified by experiments. This work opens an avenue for scalable, fluorine‐free dry synthesis of MXenes with compositions and surface chemistries that are not accessible using wet chemical etching.

Driving the pseudocapacitive redox intercalation in 2DMXenes with neutral electrolytes is important for safer, more sustainable, and improved electrochemical charge storage. Single transition metal MXenes, such as Ti₃C₂, have shown great promise for energy storage, owing to their high conductivity and redox activity. Mixed metallic MXenes, such as out‐of‐plane ordered Mo₂Ti₂C₃, have remained underexplored in energy storage because of the absence of redox activity in most of the electrolytes. Simultaneous structural modifications and instigating intercalation pseudocapacitance in neutral electrolytes could be a viable strategy for enhancing their electrochemical properties. Herein, a facile synthesis of partially oxidized Mo₂Ti₂C₃MXene (PO‐Mo₂Ti₂C₃) exhibiting improved charge storage capability is demonstrated. Optical, structural, and spectroscopic analyses indicate the formation of oxide nanostructures upon thermal oxidation of Mo₂Ti₂C₃. This leads to an enhanced energy storage capability with remarkably improved cyclability as well as a high Coulombic efficiency in a neutral LiCl electrolyte. This work highlights the importance of structural modifications of MXenes to enhance their charge storage and shows the promise of less explored double transition metal MXenes in energy storage.

MXenes constitute a rapidly growing family of 2D materials that are promising for optoelectronic applications because of numerous attractive properties, including high electrical conductivity. However, the most widely used titanium carbide (Ti₃C₂T_x) MXene transparent conductive electrode exhibits insufficient environmental stability and work function (WF), which impede practical applications Ti₃C₂T_xelectrodes in solution‐processed optoelectronics. Herein, Ti₃C₂T_xMXene film with a compact structure and a perfluorosulfonic acid (PFSA) barrier layer is presented as a promising electrode for organic light‐emitting diodes (OLEDs). The electrode shows excellent environmental stability, highWFof 5.84 eV, and low sheet resistanceR_Sof 97.4 Ω sq⁻¹. The compact Ti₃C₂T_xstructure after thermal annealing resists intercalation of moisture and environmental contaminants. In addition, the PFSA surface modification passivates interflake defects and modulates theWF. Thus, changes in theWFandR_Sare negligible even after 22 days of exposure to ambient air. The Ti₃C₂T_xMXene is applied for large‐area, 10 × 10 passive matrix flexible OLEDs on substrates measuring 6 × 6 cm. This work provides a simple but efficient strategy to overcome both the limited environmental stability and lowWFof MXene electrodes for solution‐processable optoelectronics.

MXenes, two‐dimensional (2D) transition metal carbides and/or nitrides, possess surface termination groups such as hydroxyl, oxygen, and fluorine, which are available for surface functionalization. Their surface chemistry is critical in many applications. This article reports amine functionalization of Ti₃C₂T_xMXene surface with [3‐(2‐aminoethylamino)‐propyl]trimethoxysilane (AEAPTMS). Characterization techniques such as X‐ray photoelectron spectroscopy verify the success of the surface functionalization and confirm that the silane coupling agent bonds to Ti₃C₂T_xsurface both physically and chemically. The functionalization changes the MXene surface charge from −35 to +25 mV at neutral pH, which allows for in situ preparation of self‐assembled films. Further, surface charge measurements of the functionalized MXene at different pH values show that the functionalized MXene has an isoelectric point at a pH around 10.7, and the highest reported positive surface charge of +62 mV at a pH of 2.58. Furthermore, the existence of a mixture of different orientations of AEAPTMS and the simultaneous presence of protonated and free amine groups on the surface of Ti₃C₂T_xare demonstrated. The availability of free amine groups on the surface potentially permits the fabrication of crosslinked electrically conductive MXene/epoxy composites, dye adsorbents, high‐performance membranes, and drug carriers. Surface modifications of this type are applicable to many other MXenes.

The cycle life of rechargeable lithium (Li)‐metal batteries is mainly restrained by dendrites growth on the Li‐metal anode and fast depletion of the electrolyte. Here, we report on a stable Li‐metal anode enabled by interconnected two‐dimensional (2D) arrays of niobium nitride (NbN) nanocrystals as the Li host, which exhibits a high Coulombic efficiency (>99 %) after 500 cycles. Combining theoretical and experimental analysis, it is inferred that this performance is due to the intrinsic properties of interconnected 2D arrays of NbN nanocrystals, such as thermodynamic stability against Li‐metal, high Li affinity, fast Li⁺migration, and Li⁺transport through the porous 2D nanosheets. Coupled with a lithium nickel–manganese–cobalt oxide cathode, full Li‐metal batteries were built, which showed high cycling stability under practical conditions – high areal cathode loading ≥4 mAh cm⁻², low negative/positive (N/P) capacity ratio of 3, and lean electrolyte weight to cathode capacity ratio of 3 g Ah⁻¹. Our results indicate that transition metal nitrides with a rationally designed structure may alleviate the challenges of developing dendrite‐free Li‐metal anodes.