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1. Overcoming the Limitations of MXene Electrodes for Solution‐Processed Optoelectronic Devices

   https://doi.org/10.1002/adma.202206377  

   Zhou, Huanyu ; Han, Shin Jung ; Lee, Hyeon‐Dong ; Zhang, Danzhen ; Anayee, Mark ; Jo, Seung Hyeon ; Gogotsi, Yury ; Lee, Tae‐Woo ( September 2022 , Advanced Materials)

   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.

    

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2. Biocompatible 3D Printed MXene Microlattices for Tissue‐Integrated Antibiotic Sensing

   https://doi.org/10.1002/admt.202301517  

   Tiwari, Anand P. ; Panicker, Sreejith S. ; Huddy, Julia E. ; Rahman, Md Saifur ; Hixon, Katherine R. ; Scheideler, William J. ( December 2023 , Advanced Materials Technologies)

   3D continuous mesoscale architectures of nanomaterials possess the potential to revolutionize real‐time electrochemical biosensing through higher active site density and improved accessibility for cell proliferation. Herein, 3D microporous Ti₃C₂T_XMXene biosensors are fabricated to monitor antibiotic release in tissue engineering scaffolds. The Ti₃C₂T_X‐coated 3D electrodes are prepared by conformal MXene deposition on 3D‐printed polymer microlattices. The Ti₃C₂T_XMXene coating facilitates direct electron transfer, leading to the efficient detection of common antibiotics such as gentamicin and vancomycin. The 3D microporous architecture exposes greater electrochemically active MXene surface area, resulting in remarkable sensitivity for detecting gentamicin (10–1 mM) and vancomycin (100–1 mM), 1000 times more sensitive than control electrodes composed of 2D planar films of Ti₃C₂T_XMXene. To characterize the suitability of 3D microporous Ti₃C₂T_XMXene sensors for monitoring drug elution in bone tissue regeneration applications, osteoblast‐like (MG‐63) cells are seeded on the 3D MXene microlattices for 3, 5, and 7 days. Cell proliferation on the 3D microporous MXene is tracked over 7 days, demonstrating its promising biocompatibility and its clinical translation potential. Thus, 3D microporous Ti₃C₂T_XMXene can provide a platform for mediator‐free biosensing, enabling new applications for in vivo monitoring of drug elution.

    

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3. Assembling 2D MXenes into Highly Stable Pseudocapacitive Electrodes with High Power and Energy Densities

   https://doi.org/10.1002/adma.201806931  

   VahidMohammadi, Armin ; Mojtabavi, Mehrnaz ; Caffrey, Nuala Mai ; Wanunu, Meni ; Beidaghi, Majid ( December 2018 , Advanced Materials)

   Electrochemical capacitors (ECs) that store charge based on the pseudocapacitive mechanism combine high energy densities with high power densities and rate capabilities. 2D transition metal carbides (MXenes) have been recently introduced as high‐rate pseudocapacitive materials with ultrahigh areal and volumetric capacitances. So far, 20 different MXene compositions have been synthesized and many more are theoretically predicted. However, since most MXenes are chemically unstable in their 2D forms, to date only one MXene composition, Ti₃C₂T_x, has shown stable pseudocapacitive charge storage. Here, a cation‐driven assembly process is demonstrated to fabricate highly stable and flexible multilayered films of V₂CT_xand Ti₂CT_xMXenes from their chemically unstable delaminated single‐layer flakes. The electrochemical performance of electrodes fabricated using assembled V₂CT_xflakes surpasses Ti₃C₂T_xin various aqueous electrolytes. These electrodes show specific capacitances as high as 1315 F cm⁻³and retain ≈77% of their initial capacitance after one million charge/discharge cycles, an unprecedented performance for pseudocapacitive materials. This work opens a new venue for future development of high‐performance supercapacitor electrodes using a variety of 2D materials as building blocks.

    

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4. Heating of Ti3C2Tx MXene/polymer composites in response to Radio Frequency fields

   https://doi.org/10.1038/s41598-019-52972-2  

   Habib, Touseef ; Patil, Nutan ; Zhao, Xiaofei ; Prehn, Evan ; Anas, Muhammad ; Lutkenhaus, Jodie L. ; Radovic, Miladin ; Green, Micah J. ( December 2019 , Scientific Reports)

   null (Ed.)

   Abstract Here we report for the first time that Ti 3 C 2 T x /polymer composite films rapidly heat when exposed to low-power radio frequency fields. Ti 3 C 2 T x MXenes possess a high dielectric loss tangent, which is correlated with this rapid heating under electromagnetic fields. Thermal imaging confirms that these structures are capable of extraordinary heating rates (as high as 303 K/s) that are frequency- and concentration-dependent. At high loading (and high conductivity), Ti 3 C 2 T x MXene composites do not heat under RF fields due to reflection of electromagnetic waves, whereas composites with low conductivity do not heat due to the lack of an electrical percolating network. Composites with an intermediate loading and a conductivity between 10–1000 S m −1 rapidly generate heat under RF fields. This finding unlocks a new property of Ti 3 C 2 T x MXenes and a new material for potential RF-based applications. 

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5. Electrical and Elastic Properties of Individual Single‐Layer Nb 4 C 3 T x MXene Flakes

   https://doi.org/10.1002/aelm.201901382  

   Lipatov, Alexey ; Alhabeb, Mohamed ; Lu, Haidong ; Zhao, Shuangshuang ; Loes, Michael J. ; Vorobeva, Nataliia S. ; Dall'Agnese, Yohan ; Gao, Yu ; Gruverman, Alexei ; Gogotsi, Yury ; et al ( February 2020 , Advanced Electronic Materials)

   2D carbides and nitrides (MXenes) are widely recognized for their exceptional promise for numerous applications. However, physical property measurements of their individual monolayers remain very limited despite their importance for revealing the intrinsic physical properties of MXenes. The first mechanical and electrical measurements of individual single‐layer flakes of Nb₄C₃T_xMXene, which are prepared via an improved synthetic method are reported. Characterization of field‐effect transistor devices based on individual single‐layer Nb₄C₃T_xflakes shows an electrical conductivity of 1024 ± 165 S cm⁻¹, which is two orders of magnitude higher than the previously reported values for bulk Nb₄C₃T_xassemblies, and an electron mobility of 0.41 ± 0.27 cm²V⁻¹s⁻¹. Atomic force microscopy nanoindentation measurements of monolayer Nb₄C₃T_xmembranes yield an effective Young's modulus of 386 ± 13 GPa, assuming a membrane thickness of 1.26 nm. This is the highest value reported for nanoindentation measurements of solution‐processable 2D materials, revealing the potential of Nb₄C₃T_xas a primary component for various mechanical applications. Finally, the agreement between the mechanical properties of 2D Nb₄C₃T_xMXene and cubic NbC suggests that the extensive experimental data on bulk carbides could be useful for identifying new MXenes with improved functional characteristics.

    

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