Lightweight energy storage devices are essential for developing compact wearable and distributed electronics, and additive manufacturing offers a scalable, low-cost approach to fabricating such devices with complex geometries. However, additive manufacturing of high-performance, on-demand energy storage devices remains challenging due to the need for stable, multifunctional nanomaterial inks. Herein, the development of 2-dimensional (2D) titanium carbide (Ti3C2Tx MXene) ink that is compatible with aerosol jet printing for energy storage applications is demonstrated. The developed MXene ink demonstrates long-term chemical and physical stability, ensuring consistent printability and achieving high-resolution prints (≈45 µm width lines) with minimal overspray. The high-resolution aerosol-jet printed MXene supercapacitor achieves an areal capacitance of 122 mF cm-2 and a volumetric capacitance of 611 F cm-3, placing them among the highest-performing printed supercapacitors reported to date. These findings highlight the potential of aerosol jet printing with MXene inks for on-demand, scalable, and cost-effective fabrication of printed electronic and electrochemical devices.

Chronic non-healing wounds represent a growing global health challenge that is poorly addressed by current advances in wound care dressings. Hyperosmotic stress linked, for example, to poor glycaemic control, is a known but under-investigated contributor to the chronic wound environment and a known inflammatory stimulus. MXene (Ti3C2Tx) has been considered for smart dressing applications but has not been investigated for use with bioactive agents to directly moderate hyperosmotic stress for improved wound care. In this study, Ti3C2Tx, in combination with osmolyte betaine, was used to investigate hyperosmotic stress-induced effects on wound closure. The effect of these materials was measured using a wound closure scratch assay, and data was used to mathematically model changes in HaCaT human keratocyte migratory rate and velocity. Changes in the upregulation of apoptotic and inflammatory markers were measured, and qualitative changes in phalloidin-labelled actin cytoskeletal structure were observed. A tert-butyl glycine betainate (tBu-GB) polyacrylate microgel loaded Ti3C2Tx dressing was then fabricated and tested for biocompatibility and slow elution of osmolyte over time. Osmotic stress at levels that did not induce cell death reduced the migratory capacity of keratocytes to close the scratch. Migration by osmotically stressed keratocytes was reduced by more than 50% at 24 h and remained at 65% (±5%) at 48 h compared to complete scratch closure at 24 h in the cell only control. This reduction was reversed by a Ti3C2Tx coating, allowing complete scratch closure by 48 h in the osmotically stressed group. Exposure of osmotically stressed cells to betaine increased normalised wound closure in the osmotically stressed keraotycte group at each time point and this was augmented by the presence of a Ti3C2Tx coating. Osmotic stress induced upregulation of inflammatory markers IL-6, IL-1α, IL-1β, CXCL1, and CXCL8 by at least 10-fold. The effect was significantly greater in the presence of bacterial LPS and this was significantly reduced by the presence of Ti3C2Tx alone and in combination with betaine. Sustained and slow release of betaine was demonstrated from a tBu-GB-microgel loaded Ti3C2Tx dressing over 48 h supporting the use of such dressings to improve osmotic stress induced, poor wound closure rates.

Triboelectric nanogenerators (TENGs) have gained recognition for their potential to convert mechanical energy into electrical energy, making them attractive for applications in healthcare, robotics, and human-device interfaces. However, many TENG devices rely on fluorinated polymers for high charge generation and involve complex fabrication processes, which limit their practicality and environmental sustainability. Here, we developed an eco-friendly composite of poly (vinyl butyral-co-vinyl alcohol-co-vinyl acetate) (PVBVA) and Ti3C2Tx MXene for extrusion printing onto aluminum foil substrates, enabling the additive manufacturing of TENGs. Experimental results indicate that integrating 5.5 mg mL-1 of MXene (P-MX 5.5) into PVBVA resulted in a power density of 760 mW & sdot;m-2, with simultaneous improvements in open-circuit voltage (129 %) and short-circuit current (250 %), demonstrating enhanced charge transfer efficiency. Beyond aluminum foil-based devices, we further explored the fully printed P-MX 5.5 TENG by utilizing silver ink electrodes, eliminating the need for aluminum foil. This fully printed, flexible TENG was successfully used for real-time human motion sensing, demonstrating its ability to detect activities such as walking, running, knee bending, and jumping. Collectively, our additively manufactured and sustainable PVBVA-MXene TENG composites, including both aluminum-based and fully printed versions, show promise for future energy harvesters, sensors, wearable electronics, healthcare, and robotic applications.

Monolayer V4C3Tz is synthesized and its atomic structure is studied using high-end transmission electron microscopy. X-Ray diffraction reveals key 3D to 2D crystal transformations as a V4AlC3 crystal is transformed into V4C3Tz in synthesis processes. The charge storage properties of V4C3Tz film electrodes are investigated for supercapacitor applications in 3 M H2SO4. V4C3Tz film electrodes shows an excellent capacitance of up to 469.6 F g−1 and 845.7 F cm−3, rate performance up to 30 A g−1 and cycling stability up to 10,000 cycles. A combination of electrochemical kinetics/mass transport models, staircase potentio-electrochemical impedance spectroscopy and in situ X-Ray absorption spectroscopy reveals, for the first time for this MXene, the underlying charge storage mechanisms, consisting of double layer capacitance, pseudocapacitance and a minor contribution from mass transport-controlled processes. The latter two implying a outstanding redox activity superior to Ti-based MXenes. The stability in standard environments, mechanical flexibility and the demonstrated excellent charge storage performance of V4C3Tz makes it one of the best candidates for supercapacitor applications, especially in miniaturized devices.

Neurotransmitters (NTs) are molecules produced by neurons that act as the body's chemical messengers. Their abnormal levels in the human system have been associated with many disorders and neurodegenerative diseases, which makes the monitoring of NTs fundamentally important. Specifically for clinical analysis and understanding of brain behavior, simultaneous detection of NTs at low levels quickly and reliably is imperative for disease prevention and early diagnosis. However, the methods currently employed are usually invasive or inappropriate for multiple NTs detection. Herein, we developed a MXene-based impedimetric electronic tongue (e-tongue) for sensitive NT monitoring, using Nb2C, Nb4C3, Mo2C, and Mo2Ti2C3 MXenes as sensing units of the e-tongue, and Principal Component Analysis (PCA) as the data treatment method. The high specific surface area, distinct electrical properties, and chemical stability of the MXenes gave rise to high sensitivity and good reproducibility of the sensor array toward NT detection. Specifically, the e-tongue detected and differentiated multiple NTs (acetylcholine, dopamine, glycine, glutamate, histamine, and tyrosine) at concentrations as low as 1 nmol L-1 and quantified NTs present in a mixture. Besides, analyses performed with interferents and actual samples confirmed the system's potential to be used in clinical diagnostics. The results demonstrate that the MXene-based e-tongue is a suitable, rapid, and simple method for NT monitoring with high accuracy and sensitivity.

MXenes are a large family of two-dimensional materials that have attracted attention across many fields due to their desirable optoelectronic, biological, mechanical and chemical properties. There currently exist many synthesis procedures that lead to differences in flake size, defects and surface chemistry, which in turn affect their properties. Herein, we describe the steps to synthesize Ti3C2Tx-the most important and widely used MXene, from a Ti3AlC2 MAX phase precursor. The procedure contains three main sections: synthesis of Ti3AlC2 MAX, wet chemical etching of the MAX in hydrofluoric acid/HCl solution to yield multilayer Ti3C2Tx and its delamination into single-layer flakes. Three delamination options are described; these use LiCl, tertiary amines (tetramethyl ammonium hydroxide/ tetrabutyl ammonium hydroxide) and dimethylsulfoxide respectively. These procedures can be adapted for the synthesis of MXenes beyond Ti3C2Tx. The MAX phase synthesis takes about 1 week, with the etching and delamination each requiring 2 d. This protocol requires users to have experience working with hydrofluoric acid, and it is recommended that users have experience with wet chemistry and centrifugation; characterization techniques such as X-ray diffraction and particle size analysis are also essential for the success of the protocol. While alternative synthesis methods, such as minimally intensive layer delamination, are desirable for certain MXenes (such as Ti2CTx) or specific applications, this protocol aims to standardize the more commonly used hydrofluoric acid/HCl etching method, which produces Ti3C2Tx with minimal concentration of defects and the highest conductivity and serves as a guideline for those working with MXenes for the first time.

In the era of the internet of things, there exists a pressing need for technologies that meet the stringent demands of wearable, self-powered, and seamlessly integrated devices. Current approaches to developing MXene-based electrochemical sensors involve either rigid or opaque components, limiting their use in niche applications. This study investigates the potential of pristine Ti3C2Tx electrodes for flexible and transparent electrochemical sensing, achieved through an exploration of how material characteristics (flake size, flake orientation, film geometry, and uniformity) impact the electrochemical activity of the outer sphere redox probe ruthenium hexamine using cyclic voltammetry. The optimized electrode made of stacked large Ti3C2Tx flakes demonstrated excellent reproducibility and resistance to bending conditions, suggesting their use for reliable, robust, and flexible sensors. Reducing electrode thickness resulted in an amplified faradaic-to-capacitance signal, which is advantageous for this application. This led to the deposition of transparent thin Ti3C2Tx films, which maintained their best performance up to 73% transparency. These findings underscore its promise for high-performance, tailored sensors, marking a significant stride in advancing MXene utilization in next-generation electrochemical sensing technologies. The results encourage the analytical electrochemistry field to take advantage of the unique properties that pristine Ti3C2Tx electrodes can provide in sensing through more parametric studies.

In this work, we engineer 2D/3D hybrid architectures or heterostructures using cost-effective and scalable layer-by-layer spray deposition methods using 2D MoS2, Ti3C2Tx as building blocks. We assemble heterostructure using a simple-to-complex strategy and systematically optimize the architecture to improve charge storage performance. The architecture and performance of the heterostructures are investigated using imaging and a variety of electrochemical methods. The optimized [(2D MoS2/CNTs)1(Ti3C2Tx/CNTs)2]x3 heterostructure showed remarkable synergystic effects in terms of capacity achieved (up to 800 mAh g-1 at 0.05 A g-1), surpassing the sum of capacities of the constituting building blocks, excellent cycling stability from low to very high rates, e.g. up to 2000 cycles at 5 A g-1 with 100 % Coulombic efficiency and capacity retention. This performance and determined predominant pseudocapacitive charge storage processes suggest applications for Li-ion capacitors. We demonstrated that by adequate tailoring of heterostructures, the drawbacks of individual nanomaterials such as the low cycling stability of 2D MoS2 can be overcome while maintaining the benefits of its high capacity. The manufacturing methods and architecture design principles here established constitute a proof of concept of the powerful potential of heterostructures in surmounting the limitations of capacity, rate performance and cycling stability of current commercial energy storage devices.

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 Mo2Ti2C3 MXene (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.

Ammonia, which is one of the most important chemicals for the synthesis of dyes, pharmaceuticals, and fertilizers, is produced by the reaction of molecular hydrogen with nitrogen, over an iron-based catalyst at 400-500 degrees C under pressure of over 100 bar. Decreasing the operating temperature and pressure of this highly energy-intensive process, developed by Haber and Bosch over 100 years ago, would decrease energy consumption in the world. In this work, we used two-dimensional Mo2CTx MXene as a support for a cobalt-based catalyst. The MXene functionalized by Co showed catalytic activity for ammonia synthesis from H-2 and N-2 at temperatures as low as 250 degrees C, without any pretreatment. The developed catalyst was highly active for ammonia synthesis, demonstrating a high rate of up to 9500 mu mol g(active phase)(-1) h(-1) at 400 degrees C under ambient pressure in steady-state conditions, and did not suffer from any deactivation after 15 days of reaction. The apparent activation energy (E-a) was found to be in the range of 68-74 kJ mol(-1), which is in line with values reported for highly active catalysts. This improved catalyst may decrease the energy consumption in the synthesis of ammonia and its derivatives, as well as facilitate the use of ammonia as a hydrogen carrier for renewable energy storage.

The MXene family has rapidly expanded since its discovery in 2011 to include nearly 50 unique MXenes, not accounting for solid solutions and diverse surface terminations. However, a question raised since their discovery has been: What is the effect of n? In other words, how does the number of layers affect the MXene properties? To date, no direct study of the impact of n has been conducted due to the lack of isoelemental MXene compositions spanning more than two n values. Herein, we report on a system of three MXenes with identical M-site chemistries, (Mo2/3V1/3)n+1CnTx (n = 1, 2, and 3), allowing for the study of MXene structure-property relationships across n, for the first time. Chemical analysis of the samples shows complete and partial ordering of the M-elements in the n = 2 and 3 samples, respectively. We show that sample stability gradually evolves as n is increased from 1 to 3, while electronic and electrochemical properties exhibit more significant changes in going from n = 1 to 2 than from n = 2 to 3.

Flexible fiber-based microelectrodes allow safe and chronic investigation and modulation of electrically active cells and tissues. Compared to planar electrodes, they enhance targeting precision while minimizing side effects from the device-tissue mechanical mismatch. However, the current manufacturing methods face scalability, reproducibility, and handling challenges, hindering large-scale deployment. Furthermore, only a few designs can record electrical and biochemical signals necessary for understanding and interacting with complex biological systems. In this study, we present a method that utilizes the electrical conductivity and easy processability of MXenes, a diverse family of two-dimensional nanomaterials, to apply a thin layer of MXene coating continuously to commercial nylon filaments (30-300 mu m in diameter) at a rapid speed (up to 15 mm/s), achieving a linear resistance below 10 Omega/cm. The MXene-coated filaments are then batch-processed into free-standing fiber microelectrodes with excellent flexibility, durability, and consistent performance even when knotted. We demonstrate the electrochemical properties of these fiber electrodes and their hydrogen peroxide (H2O2) sensing capability and showcase their applications in vivo (rodent) and ex vivo (bladder tissue). This scalable process fabricates high-performance microfiber electrodes that can be easily customized and deployed in diverse bioelectronic monitoring and stimulation studies, contributing to a deeper understanding of health and disease.

Fourier-transform infrared (FTIR) spectroscopy characterization is a powerful and easy-to-use technique frequently employed for the characterization and fingerprinting of materials. Although MXenes are a large and fastest growing family of inorganic 2D materials, the lack of systematic FTIR spectroscopy studies hinders its application to MXenes and often leads to misinterpretation of the results. In this study, we report experimental and calculated FTIR spectra of 12 most typical carbide and carbonitride MXenes with different compositions (5 transition metals) and all four basic structures, including Ti2CT x , Nb2CT x , Mo2CT x , V2CT x , Ti3C2T x , Ti3CNT x , Mo2TiC2T x , Mo2Ti2C3T x , Nb4C3T x , V4C3T x , Ta4C3T x , and Mo4VC4T x . The measurements were performed on delaminated MXene flakes incorporated in KBr pellets in the 4000-400 cm-1 range. We provide detailed instructions for sample preparation, data collection, and interpretation of FTIR spectra of MXenes. Background correction and spectra smoothing are applied to obtain clear FTIR peaks corresponding to bond vibrations in MXenes. Density functional theory calculations were used for the precise assignment of all characteristic FTIR peaks and an in-depth analysis of the vibration modes. This work aims to provide the 2D material community with the FTIR spectroscopy technique as a reliable method for identifying and analyzing MXenes.

Abstract Deepening our understanding of immune cell behavior is vital for creating safe, effective treatments, particularly as immune cell therapy, also known as cellular immunotherapy or cell-based immunotherapy, represents a groundbreaking approach in the treatment of various diseases, including cancer. Transition metal carbides and nitrides (MXenes), a novel family of 2D nanomaterials, show promise as advanced trackers for immune cells—key for precise diagnostics and therapies. Traditional cell labeling methods have stagnated due to limited chemical options, impeding progress in applied medicine. Moreover, these methods are incompatible with single-cell mass cytometry by time-of-flight (CyTOF), a globally adopted technology that improves classical flow cytometry. We propose an innovative solution utilizing MXenes to overcome these challenges. Our method, Label-free sINgle-cell tracKing of 2D matErials by mass cytometry (LINKED), leverages a novel, biocompatible, multiplexed, label-free detection approach via CyTOF and Mass Ion Beam Imaging by Time-of-Flight (MIBI-TOF). This technique overcomes chemical limitations and integrates seamlessly with CyTOF, allowing for nanomaterial detection and simultaneous measurement of diverse immune cell and tissue features. Our work promises to advance immunological research significantly, offering refined cell labeling and tracking techniques crucial for the advancement of translational medicine.

Electrospray deposition (ESD) uses strong electric fields applied to solutions and dispersions exiting a capillary to produce charged monodisperse droplets driven toward grounded targets. Self-limiting electrospray deposition (SLED) is a phenomenon in which highly directed, uniform, and even 3D coatings can be achieved by trapping charge in the deposited film, redirecting the field lines to uncoated regions of the target. However, when inorganic particles are added to SLED sprays, the buildup of charge required to repel incoming material is disrupted as particle loading increases. Due to its fibril gelling behavior, methylcellulose (MC) SLED can form nanowire morphologies. These wires, when used as a binder, can separate particles and prevent percolation. In this work, a variety of conductive and insulating particles are explored using patterned and un-patterned substrates. This exploration allows us to maximally load particles for high-concentration and highly controlled self-limiting functional sprays. This is demonstrated using Ti3C2Tx MXene to functionalize an interdigitated electrode for use as a supercapacitor.

Vanadium and niobium oxides have been identified as promising electrodes for electrochemical energy storage applications as their constituent transition metals can undergo multiple reduction steps leading to high specific capacities during cycling. MXenes are attractive precursors for these compounds due to their tunable compositions and 2D nanoscale morphology. Herein, we demonstrate the synthesis of a wide range of solid -solution (NbyV2-y)AlC MAX phases, their chemical etching to produce (NbyV2-y)CTx MXenes, and the subsequent oxidation of MXenes to form respective oxides. We show that the formation of solid solutions facilitated the etching kinetics of MAX phase powder and accelerated MXene formation compared to pure vanadium and niobium carbides. Oxidation of V2CTx and Nb2CTx produced bilayered vanadium oxide (BVO) with a crumpled nanosheet morphology and nanostructured amorphous Nb2O5 (nANO) nanospheres, respectively. For oxides derived from solid-solution MXenes, scanning electron microscopy imaging revealed the growth of nANO on the surface of BVO nanosheets. Electrochemical cycling of (NbyV2-y)CTx-derived oxides in Li-ion cells revealed varying intercalation-like behavior with electrodes derived from V2CTx showing redox processes and nANO exhibiting pseudocapacitive response. The CV curves of solid-solution MXene-derived oxides demonstrated primarily BVO/nANO composite-like behavior, with key exceptions. The cells containing Nb0.25V1.75CTx-derived oxide showed a large capacity of 296.8 mA h g(-1) driven by significant electrochemical activity at all potentials along the sweep possibly stemming from niobium doping into BVO structure. The Nb1.00V1.00CTx-derived oxide electrode delivered a specific capacity of 298 mA h g(-1) with contributions from both, BVO and nANO phases. The improved electrochemical stability of (Nb1.00V1.00)CTx-derived oxide electrodes compared to an electrode prepared by physically mixing Nb2CTx -derived oxide with V2CTx -derived oxide with the same Nb/V molar ratio was attributed to the stabilizing effect of the BVO/nANO heterointerface. Our work indicates that the use of solid-solution MXenes as precursors is an attractive strategy to synthesize oxides with compositions, morphologies, and properties that cannot be produced otherwise.

Selective and ultrathin films and coatings capable of controlling infrared (IR) emission are crucial for highly integrated thermal management systems, but are challenging produce using conventional materials. Here, we report that the MXene family of two-dimensional carbides and carbonitrides offers a broad range of IR emissivity values (-0.06-0.59) with diverse colors, varying with MXene composition and structure. Specifically, 200 nm thick purple Ti3C2TX coating has an average IR emissivity of 0.06, while gold Nb2CTX coating is 0.59 at wavelengths from 3-25 lm. We demonstrate that the IR emissivity can be finely tuned by combining different metals in solid-solution MXenes. Furthermore, the IR identification capability at varying temperatures was validated using different MXene coatings and patterned MXene fabrics. The versatility of MXenes at optical and infrared wavelengths provides a platform for developing MXene-based smart, flexible devices and wearables capable of selective and localized thermal management, aiming at radiative heating/cooling, IR identification, photothermal conversion, and thermal imaging.

High electrical conductivity is desired in MXene films for applications such as electromagnetic interference shielding, antennas, and electrodes for electrochemical energy storage and conversion applications. Due to the acid etching-based synthesis method, it is challenging to deconvolute the relative importance that factors such as chemical composition and flake size contribute to resistivity. To understand the intrinsic and extrinsic contributions to the macroscopic electronic transport properties, a systematic study controlling compositional and structural parameters was conducted with eight solid solutions in the Ti y Nb 2− y CT x system. In particular, we investigated the different roles played by metal (M)-site composition, flake size, and d -spacing on macroscopic transport. Hard x-ray photoemission spectroscopy and spectroscopic ellipsometry revealed changes to electronic structure induced by the M-site alloying. Consistent with the spectroscopic results, the low- and room-temperature conductivities and effective carrier mobility are correlated with the Ti content, while the impact of flake size and d -spacing is most prominent in low-temperature transport. The results provide guidance for designing and engineering MXenes with a wide range of conductivities.