Lithium–sulfur (Li–S) batteries are one of the main challenges facing Li-ion technology because the insulating nature of sulfur and the shuttle phenomenon of dissolved lithium polysulfides (LPSs) in liquid electrolytes result in critical problems, including low Coulombic efficiency, loss of active material, and rapid capacity decay. Here, we oxidized delaminated transition metal carbides (MXenes) using CO2 (Oxi-d-MXenes) and used them as both cathode electrode with sulfur and modified separator coated onto the glass fiber without a conductive material and binder to suppress the diffusion of LPSs. Oxi-d-MXenes annealed at 900 °C using CO2 gas formed perfectly converted rutile-TiO2 nanocrystalline particles on their two-dimensional sheets. Li–S batteries fabricated with the Oxi-d-MXenes cathode and the Oxi-d-MXenes-modified separator exhibited high Coulombic efficiency (nearly 99%) and retained a capacity of about 900 mAh g–1 after 300 cycles at a current density of 1C. These results were attributed to the chemical and physical adsorption between the Oxi-d-MXenes and the LPSs. Our results imply that Oxi-d-MXenes prepared by the CO2 treatment exhibit physical and electrochemical properties that enhance the performance of Li–S batteries.

Thin films of well‐stacked two‐dimensional MXene flakes have been used in various applications, especially in sensors and microscale energy storage devices, such as micro‐supercapacitors. Miniaturization and integration of devices, as well as maximization of device performance require nanoscale patterning of MXene, beyond what can be achieved using inkjet or screen printing. However, nanoscale patterning technology for MXene is yet to be developed. In the present work, a simple fabrication method is demonstrated for manufacturing Ti3C2Tx MXene films with vertically aligned nanopatterns via soft lithography. This process involves polydimethylsiloxane (PDMS) stamping with line‐patterned PDMS molds. The feature size of the vertical line patterning of MXene is controlled with the nanometers accuracy by swelling of the PDMS mold by toluene, which also guides vertical alignment of MXene flakes. As a result, vertically aligned MXene nanopatterns are fabricated with a width of ridges less than 200 nm and 2‐µm regular spacing between the ridges. The oleylamine‐functionalized MXene flakes are also developed for better dispersion in toluene, providing a general protocol to fabricate MXene dispersions in nonpolar solvents.

2D transition metal carbides (MXenes) obtained from bulk Mn+1AXn (n = 1, 2, 3, or 4) phases are an intriguing class of crystalline solids with unique physicochemical properties for promising applications such as batteries, capacitive energy storage, and electrocatalysis. One of the obstacles that must be overcome for technical applications is that MXene flakes delaminated in aqueous conditions suffer from phase transition and/or structural decomposition over time. Herein, a simple but powerful strategy to enhance their stability by passivating vulnerable edges on the delaminated MXene (Ti3C2Tx) with heterocyclic aromatic amines is reported. In particular, pyrrole‐functionalized MXenes are found to facilitate anti‐oxidation in aqueous solutions at room temperature over 700 days, at 70 °C over 42 days, and even with a strong oxidizer (H2O2, 9.70 mmol) over 50 days. On the other hand, the as‐prepared MXene solution lost its color within a month at room temperature, a day at 70 °C, and 5 min in the presence of H2O2 (9.70 mmol). Density functional theory calculations indicate that chemical interactions between MXene and pyrrole are extremely strong and involve the formation of TiC bonds. Furthermore, pyrrole‐functionalized MXenes exhibit higher electrochemical performance than pristine MXenes as a supercapacitor.

Ultra‐Stable MXenes In article number 2203296, Yonghee Lee, Chi Won Ahn, Mu‐Hyun Baik, and co‐workers demonstrate a simple and powerful strategy in the preservation of titanium carbide MXene (Ti3C2Tx) phases with long‐lasting stability in aqueous environments. Pyrrole‐functionalized MXenes were found to facilitate anti‐oxidation at room temperature over 700 days, at 70 °C over 42 days, and even with a strong oxidizer (H2O2) over 50 days.