Two-dimensional Transition Metal Carbides Research Articles

(Invited) Tunable Chemistry of 2D Carbide Mxenes for Hydrogen Evolution Reaction

Two-dimensional (2D) transition metal carbides and nitrides (MXenes) are a large family of earth-abundant materials with more than forty compositions synthesized since 2011, such as Ti2CT x , Mo2CT x , Nb2CT x , Ti3C2T x , Mo2TiC2Tx, and Mo2Ti2C3T x . MXenes have emerged as promising candidates for catalytic energy storage and conversion because their 2D surfaces are electrochemically active combined with MXenes’ hydrophilicity, high electrical conductivity, and affinity to bond to molecules and nanomaterials to form hybrid structures. MXenes electrochemical properties can be tuned by the control of multiple variables: in the MXene formula of M n +1X n T x , the transition metals (M) can be any of the groups 4, 5, 6 of the periodic table or their combination, X can be carbon, nitrogen, or a solid solution of both, surface terminations (T x ) can be any of the group 16 and 17, and the ‘n’ (MXene 2D flake thicknesses) can be 1 to 4. In this talk, we will discuss the control of MXene transition metals, their thicknesses, and surfaces to tune their electrocatalytic behavior. Specifically, we present a systematic study of 20 different MXenes, including novel compositions such as W2TiC2T x and Mo2Nb2C3T x and high-entropy MXenes, and discuss how we achieve low overpotential for hydron evolution reaction (as low as ~160 mV).

Elucidating the Interactions between Different Transition Metal Cations and Ti3C2Tx MXene through Intercalation Method for Electrochemical Applications

MXenes, are a family of two-dimensional (2D) transition metal carbides, nitrides and/ or carbonitrides.[1] The intercalation of different metal cations and organic molecules into MXene for tuning MXenes’ electronic and electrochemical properties have been widely reported.[2] [3] [4] However, transition metals (TMs) which have distinct electrochemical behaviors[5] [6] have not been explored in the literature of MXenes’ intercalation. Therefore, we herein compared the intercalation effects of different TM cations on Ti3C2Tx, for offering a general insight on the influences of multi-valent, redox-active TMs on MXenes. In particular, the changes on the physiochemical and electrochemical properties of MXenes were investigated using different in-situ and ex-situ methods, for a better understanding on the interfacial interactions of TM cations and MXenes in the confined environment of MXenes’ multilayer structures. This work serves as a foundation for the fine-tuning of MXenes’ properties by utilizing a variety of TM cations intercalation for different electrochemical systems.[1] B. Anasori, M. R. Lukatskaya, Y. Gogotsi, Nature Reviews Materials 2017, 2, 16098.[2] M. R. Lukatskaya, O. Mashtalir, E. Ren Chang, Y. Dall’Agnese, P. Rozier, L. Taberna Pierre, M. Naguib, P. Simon, M.W. Barsoum, Y. Gogotsi, Science 2013, 341, 1502-1505.[3] J. Li, H. Wang, X. Xiao, Energy & Environmental Materials 2020, 3, 306-322[4] M. Ghidiu, S. Kota, J. Halim, A. W. Sherwood, N. Nedfors, J. Rosen, V. N. Mochalin, M. W. Barsoum, Chemistry of Materials 2017, 29, 1099-1106.[5] D. Göhl, H. Rueß, M. Pander, A. R. Zeradjanin, K. J. J. Mayrhofer, J. M. Schneider, A. Erbe, M. Ledendecker, Journal of The Electrochemical Society 2020, 167, 021501.[6] M. Esmaeilirad, A. Baskin, A. Kondori, A. Sanz-Matias, J. Qian, B. Song, M. Tamadoni Saray, K. Kucuk, A. R. Belmonte, P. N. M. Delgado, J. Park, R. Azari, C. U. Segre, R. Shahbazian-Yassar, D. Prendergast, M. Asadi, Nature Communications 2021, 12, 5067.

Shrinking Lithium-Ion Batteries by Replacing Metal Current Collectors with MXene Films

The demand for high-performance energy storage devices has been rapidly increasing due to the growing need for renewable energy integration and portable electronics. Traditional lithium-ion batteries have become the preferred choice for numerous applications due to their impressive energy density, but they are reaching limitations of capacity. At the cell level, around 25 w% consists of passive components like current collectors, conductive additives, binders, and separators. Especially, copper (Cu) and aluminum (Al) foils have been commonly used as current collectors for the anode and cathode in lithium-ion batteries (LIBs), contributing around 7 wt% and 8 wt%, respectively, to the overall weight. Despite constituting a considerable portion of the battery, these passive components often receive less attention in the development of high-power batteries. In recent years, the focus has been on decreasing the thickness of these metal current collectors and developing lightweight alternative materials to enhance energy efficiency to potentially boost the performance metrics of a Li-ion battery cell to boost the performance metrics of a Li-ion battery cell. MXenes, a family of two-dimensional transition metal carbides, nitrides, and carbonitrides emerge as a promising solution to address this limitation. In particular, Ti3C2T x MXene possesses a 2D morphology with excellent electrical conductivity (up to 20,000 S/cm), high surface area, good mechanical properties, and hydrophilicity. These attributes, coupled with ease of processing, make it very suitable for battery passive components. In this study, we focus on replacing the conventional copper current collector with thinner MXene film current collectors for high-mass loading graphite anode electrodes. Our results show improved capacities and rate performances of electrode materials using Ti3C2T x MXene current collectors while also reducing electrode weight and thickness. The electrode-level gravimetric capacity significantly increased by 98.5 mAh g-1 (from 140 mAh g-1 for Cu@graphite to 238.5 mAh g-1 for MXene@graphite). The areal and volumetric capacities increased as well. This study highlights the potential of MXene current collectors in improving the performance of lithium-ion batteries, paving the way for more efficient and lightweight energy storage solutions.

Theoretical Investigation of a Novel Two-Dimensional Non-MXene Mo3C2 as a Prospective Anode Material for Li- and Na-Ion Batteries.

A new two-dimensional (2D) non-MXene transition metal carbide, Mo3C2, was found using the USPEX code. Comprehensive first-principles calculations show that the Mo3C2 monolayer exhibits thermal, dynamic, and mechanical stability, which can ensure excellent durability in practical applications. The optimized structures of Lix@(3×3)-Mo3C2 (x = 1-36) and Nax@(3×3)-Mo3C2 (x = 1-32) were identified as prospective anode materials. The metallic Mo3C2 sheet exhibits low diffusion barriers of 0.190 eV for Li and 0.118 eV for Na and low average open circuit voltages of 0.31-0.55 V for Li and 0.18-0.48 V for Na. When adsorbing two layers of adatoms, the theoretical energy capacities are 344 and 306 mA h g-1 for Li and Na, respectively, which are comparable to that of commercial graphite. Moreover, the Mo3C2 substrate can maintain structural integrity during the lithiation or sodiation process at high temperature. Considering these features, our proposed Mo3C2 slab is a potential candidate as an anode material for future Li- and Na-ion batteries.

Hierarchical porous microrod In2O3@C@Ti3C2TX composite anode for high-performance lithium-ion batteries

In2O3, employed as an anode, demonstrates exceptional capacity in lithium-ion batteries (LIBs). Nonetheless, its propensity for significant volume expansion results in internal fracturing and reorganization. Two-dimensional double transition metal carbides and nitrides (MXenes), characterized by unique out-of-plane metal atom ordering, exhibit promising electrical properties due to their chemical versatility and intricate structure. However, MXenes' tendency to aggregate or stack into lamellar structures impedes their practical energy storage application. To address these issues, a hierarchical porous microrods In2O3@C@Ti3C2TX (HPMR-In2O3@C@Ti3C2TX) composite anode material was synthesized through electrostatic self-assembly of MIL-68 (In) and Ti3C2TX, followed by carbonization. This synthesis produced continuous one-dimensional microrods with hierarchical porous channels in HPMR-In2O3@C, offering a substantial specific surface area, numerous Li+ storage sites, and enhanced charge transfer rates. Moreover, the interlayer space within Ti3C2TX acts as an electrolyte reservoir, facilitating comprehensive electrochemical reactions and accommodating volume changes during charge-discharge cycles. Consequently, the HPMR-In2O3@C@Ti3C2TX anode exhibited remarkable properties, including a high initial discharge specific capacity of 1406 mAh g-1 at 0.1 C, outstanding cycling performance, and superior rate performance. This research presents a promising direction for the advancement of high-performance anode materials for lithium-ion batteries.

Mechanism of the Terahertz Wave-MXene Interaction and Surface/Interface Chemistry of MXene for Terahertz Absorption and Shielding.

ConspectusOver the past two decades, terahertz (THz) technology has undergone rapid development, driven by advancements and the growing demand for THz applications across various scientific and technological domains. As the cornerstone of THz technology, strong THz-matter interactions, especially realized as high THz intrinsic absorption in nanometer-thick materials, play a highly important role in various applications including but not limited to THz absorption/shielding, detection, etc. The rigorous electromagnetic theory has posited a maximum intrinsic absorption of 50% for electromagnetic waves by thin films, and the succinct impedance matching condition has also been formulated to guide the design of highly intrinsically absorbing materials. However, these theories face challenges when applied to the THz spectrum with an ultrabroad bandwidth. Existing thin films typically achieve a maximum intrinsic absorption within a narrow frequency range, significantly limiting the performance of THz absorbers and detectors. To date, both theoretical frameworks and experimental solutions are lacking in overcoming the challenge of achieving broadband maximum intrinsic absorption in the THz regime.In this Account, we describe how two-dimensional (2D) transition-metal carbide and/or nitride (MXene) films with nanometer thickness can realize the maximum intrinsic absorption in the ultrabroad THz band, which successfully addresses the forementioned longstanding issue. Surprisingly, traditional DC impedance matching theory fails to explain this phenomenon, while we instead propose a novel theory of AC impedance matching to provide a satisfactory explanation. By delving into the microscopic transport behavior of free electrons in MXene, we discover that intraflake transport dominates terahertz conductivity under THz wave excitation, while interflake transport primarily dictates DC conductivity. This not only elucidates the significant disparities between DC and AC impedance in MXenes but also underscores the suitability of AC impedance matching for achieving broadband THz absorption limits. Furthermore, we identify a high electron concentration and short relaxation time as crucial factors for achieving broadband maximum absorption in the THz regime. Although approaching the THz intrinsic absorbing limits, it still faces hurdles to the use of MXene in practical applications. First, diverse and uncontrollable terminations exist on the surface of MXene stemming from the synthesis process, which largely influence the electron structure and THz absorbing property of MXene. Second, MXene suffers from poor stability in the presence of oxygen and water. To address the above issues, we have undertaken distinctive works to precisely control the terminations and suppress the oxidation of MXene even at high temperature through surface and interface chemistry, such as low-temperature Lewis basic halide treatment and building a Ti3C2Tx/extracted bentonite (EB) interface. For practical application consideration, we proposed a copolymer-polyacrylic latex (PAL)-based MXene waterborne paint (MWP) with a strong intermolecular polar interaction between MWP and the substrate provided by the cyano group in PAL. This not only has strong THz EMI shielding/absorption efficiency but also can easily adhere to various substrates that are commonly used in the THz band. These studies may have significant implications for future applications of MXene nanofilms in THz optoelectronic devices.

Rational design of MXene-based vacancy-confined single-atom catalyst for efficient oxygen evolution reaction

Two-dimensional transition metal carbides (MXenes) have been demonstrated to be promising supports for single-atom catalysts (SACs) to enable efficient oxygen evolution reaction (OER). However, the rational design of MXene-based SACs depends on an experimental trial-and-error approach. A theoretical guidance principle is highly expected for the efficient evaluation of MXene-based SACs. Herein, high-throughput screening was performed through first-principles calculations and machine learning techniques. Ti3C2(OH)x, V3C2(OH)x, Zr3C2(OH)x, Nb3C2(OH)x, Hf3C2(OH)x, Ta3C2(OH)x, and W3C2(OH)x were screened out based on their excellent stability. Zn, Pd, Ag, Cd, Au, and Hg were proposed to be promising single atoms anchored in MXenes based on cohesive energy analysis. Hf3C2(OH)x with a Pd single atom delivers a theoretical overpotential of 81 mV. Both moderate electron-deficient state and high covalency of metal–carbon bonds were critical features for the high OER reactivity. This principle is expected to be a promising approach to the rational design of OER catalysts for metal-air batteries, fuel cells, and other OER-based energy storage devices.

Identifying the presence of subsurface oxygen on the Ti3C2 MXene using H2O as a probe molecule: A DFT study

Oxycarbide MXenes are two-dimensional transition metal carbides with subsurface oxygen content within their carbon layers. Substitutional oxygen atoms are thermodynamically very stable, impose virtually no lattice strain on their surroundings, and do not change the metallic behaviour of Ti3C2, making them very difficult to detect experimentally. Here, water is suggested as a probe to identify subsurface oxygen atoms on the H2-exposed and heat pre-treated Ti3C2 MXene. Independently of the oxygen concentration, density functional theory calculations show that water can adsorb near subsurface oxygen atoms as well as on stoichiometric Ti3C2 regions of the material and is deemed appropriate for identifying substitutional oxygen defects on Ti3C2 through frequency analysis. The calculated stretching mode of water increases by at least 67 cm−1 in the presence of subsurface oxygen, allowing the experimental detection of this defect, even at the lowest concentration considered, i.e., a replacement of 3 % of carbon by oxygen atoms.

A first-principles study of the lithium storage properties of transition metal doped TM-Ti2CO2 (TM=Sc, V, Cr, Mn, Fe, Co, Ni and Cu)

Two-dimensional transition metal carbides, known as MXenes, have garnered significant interest for their potential applications in lithium-ion batteries anode materials, owing to their distinctive properties. Doping, a prevalent method for material modification, involves the substitution of metal atoms within MXenes with other elements to modulate material properties. Given that MXenes inherently contain transition metals, doping with additional transition metals presents an optimal approach for enhancing their performance. In this study, we investigated the effect of doping eight transition metals (Sc, V, Cr, Mn, Fe, Co, Ni, Cu) onto Ti2CO2, aiming to elucidate their impact on the lithium storage properties of the material. Our findings reveal that the introduction of different dopant atoms induces changes in the d-band center of the material, consequently influencing the adsorption energy of lithium ions on the MXene surface in a nearly linear fashion. What’s more, doping with Sc, Cr, and Mn atoms results in an elevation of the migration energy, while doping with Fe, Co, Ni, and Cu atoms leads to a notable increase in the open circuit voltage (OCV). Remarkably, only V atom doping demonstrates an optimal combination of suitable adsorption energy, OCV (0.66 V), and minimal diffusion energy (0.11 eV). These results underscore the significance of transition metal doping in tailoring the lithium storage properties of MXene-based anode materials, offering insights for the design and optimization of next-generation lithium-ion batteries.

Nb2C and Nb2CO2 MXenes as Anodes in Li-Ion Batteries: A Comparative Study by First-Principles Calculations.

The new generation of Li-ion batteries is based on integrating 2D materials into the electrodes to increase the energy density while reducing the charging time and size. The two-dimensional transition metal carbide or nitride (MXene) materials offer ideal electronic properties, such as metallic behavior, low energy barriers for Li-ion diffusion, and structural stability. This study focuses on Nb2C and Nb2CO2 MXenes, which have shown promising Li-storage capacity, especially the oxidized phase. By using density functional theory (DFT) and thermodynamic criteria, we studied the Li intercalation process in both MXenes. The results show that the Li intercalation process in the oxidized phase is more stable. Also, the Li diffusion barriers are 35 and 250 meV for the bare and oxidized phase, due to the strong interaction between Li ions and O functional groups. Nb2C and Nb2CO2 MXenes deliver a maximum gravimetric theoretical capacity of 275 and 233.26 mA h/g, respectively, with a stable performance.

Tailoring the ion storage of MXene by aramid nanofibers towards self-standing electrodes for flexible solid-state supercapacitors

Two-dimensional (2D) transition metal carbides and nitrides (MXenes) are a class of 2D nanomaterials that can offer excellent properties for high-performance supercapacitors. Nevertheless, irreversible restacking of MXene sheets decreases the interlayer spacing, which inhibits the ion intercalation between the MXene nanosheets and finally deteriorates the electrochemical performance of supercapacitors. Herein, aramid nanofibers (ANFs) are mixed with Ti3C2T x MXene to prepare MXene/ANFs composite films. The restacking of MXene sheets is inhibited by the electrostatic repulsion between ANFs and MXene. The ANFs act as intercalation agents to increase the interlayer spacing of the composite films, which can improve the ion storage ability of supercapacitors. Furthermore, the ANFs enhance the mechanical strength of the composite films due to the strong hydrogen bonding interaction and nanomechanical interlocking between ANFs and MXene, endowing the composite films with self-standing property. The resultant composite films are used as electrodes for flexible solid-state supercapacitors to achieve high specific capacitance (996.5 mF cm−2 at 5 mV s−1) and outstanding cycling stability. Thus, this work provides a potential strategy to regulate the properties of 2D nanomaterials, which may expand the application of them in energy storage, ionic separation, osmotic energy conversion and beyond.

First-principles study of two-dimensional transition metal carbide M n+1 C n O2 (M = Nb,Ta)

In the present work, the three stable MXenes M n+1 C n O2 (M = Nb,Ta) are explored based on first-principles calculations. These materials are important derivatives of 2D materials and exhibit distinctive properties, holding vast potential in nanodevices. All these M n+1 C n O2 (M = Nb,Ta) materials exhibit outstanding superconducting performance, with corresponding superconducting transition temperatures of 23.00 K, 25.00 K, and 29.00 K. Analysis reveals that the high superconducting transition temperatures of MXenes M n+1 C n O2 (M = Nb,Ta) are closely associated with the high value of the logarithmic average of phonon frequencies, ωlog , and the strong electron–phonon coupling, attributed to the crucial contribution of low-frequency phonons. Additionally, we applied strain treatments of 2% and 4% to M n+1 C n O2 (M = Nb,Ta), resulting in varying changes in superconducting transition temperatures under different strains.

Stretchable MXene/Carbon Nanotube Bilayer Strain Sensors with Tunable Sensitivity and Working Ranges.

Stretchable strain sensors have gained increasing popularity as wearable devices to convert mechanical deformation of the human body into electrical signals. Two-dimensional transition metal carbides (Ti3C2Tx MXene) are promising candidates to achieve excellent sensitivity. However, MXene films have been limited in operating strain ranges due to rapid crack propagation during stretching. In this regard, this study reports MXene/carbon nanotube bilayer films with tunable sensitivity and working ranges. The device is fabricated using a scalable process involving spray deposition of well-dispersed nanomaterial inks. The bilayer sensor's high sensitivity is attributed to the cracks that form in the MXene film, while the compliant carbon nanotube layer extends the working range by maintaining conductive pathways. Moreover, the response of the sensor is easily controlled by tuning the MXene loading, achieving a gauge factor of 9039 within 15% strain at 1.92 mg/cm2 and a gauge factor of 1443 within 108% strain at 0.55 mg/cm2. These tailored properties can precisely match the operation requirements during the wearable application, providing accurate monitoring of various body movements and physiological activities. Additionally, a smart glove with multiple integrated strain sensors is demonstrated as a human-machine interface for the real-time recognition of hand gestures based on a machine-learning algorithm. The design strategy presented here provides a convenient avenue to modulate strain sensors for targeted applications.

Tunable superconductivity in fluorine-functionalized molybdenum carbide

Two-dimensional transition metal carbide, molybdenum carbide (Mo2C), has been explored for applications in catalysts, energy storage devices, and superconductors. Generally, selectively etching Ga from Mo2Ga2C in HF solution is the most popular method for synthesizing Mo2CTx, where Tx represents the surface functional group (−O, –OH, –F). The functional groups on their surface strongly influence the density of states on the Fermi surface and thereby the electronic structure. Therefore, tailoring the surface functionalization demonstrates a great potential for tuning the electronic properties of Mo2C. To precisely investigate the effect of the fluorine functional group on the superconductivity of Mo2C, we adopted the topochemical method to synthesize 2D Mo2C. The fluorine-functionalized Mo2C was obtained by sintering the mixture of Mo2C and NH4F in different ratios, in which NH4F was considered a fluorine source. Due to the strong electronegativity of fluorine, the surface of Mo2C was easily functionalized by fluorine. Notably, the superconductivity of Mo2C was enhanced by increasing the fluorine content and reached the highest Tc value of 5.7 K, compared with 3.2 K of pure Mo2C. A clear magnetization hysteresis loop was observed at 2.0 K, indicating a typical type-II superconductor.

Molecular dynamics simulations of ionic liquids confined into MXenes

Two-dimensional (2D) transition metal carbides known as MXenes have been extensively investigated as electrode material of electrochemical devices, including supercapacitors. Here we present a detailed computational study of ionic liquids in contact with Ti3C2F2, both at planar surface and under confinement. The simulations employ an extension of the constant potential model (CPMχ) that can properly deal with materials composed of chemical elements with different electronegativities. The average partial charges of MXene atoms calculated with CPMχ are in excellent agreement with the ones obtained by DFT calculations. The differential capacitance and the charging mechanisms are thoroughly analyzed for two ionic liquids with a common cation, [EMIM][BF4] and [EMIM][NTf2]. By varying the MXene interlayer dimension, the best performance in terms of charge storage is obtained in electrodes with 12.6 Å spacing, with outperformance of [EMIM][BF4]-based cells.

Ultrasonication-assisted synthesis of transition metal carbide of MXene: an efficient and promising material for photocatalytic organic dyes degradation of rhodamine B and methylene blue in wastewater.

Water pollutants of non-biodegradable toxic aromatic dye including Methylene blue (MB) and Rhodamine (RhB) are extremely carcinogenic thiazines used in various industries such asleather industry, paper industry, and the dyeing industry. The presence of dyes in wastewater causes severe threats to human health that are responsible for various harmful chronic or acute diseases and also shows an adverse impact on the environment as it reduces transparency and is harmful to water microorganisms. To overcome severe issues, many traditional techniques have been used to remove toxic pollutants, but thesemethods are insufficient to remove chemically stable dyes that remain in the treated wastewater. However, the photocatalytic degradation process is an efficient approach to degrade the dye up to the maximum extent with improved efficiency. Therefore, in this work, a new class of two-dimensional (2D) transition metal carbide of Titanium Carbide (Ti3C2Tx) MXene material was used for the organic dyes degradation such as MB and RhB using a photocatalytic process. A layered structure of hexagonal lattice symmetry of Ti3C2Tx MXene was successfully synthesized from the Titanium Aluminum Carbide ofTi3AlC2 bulk phase using an exfoliation process. Further, the XRD spectrum confirms the transformation of bulk MAX phase having (002) plane at 9.2° to Ti3C2Tx MXene of (002) plane at 8.88° confirms the successful removal of Al layer from MAX phase. A smooth, transparent, thin sheet-like morphology of Ti3C2Txnanosheet sizewere found to be in the range of 70 to 150nm evaluated fromTEM images. Also,no holes or damages in the thin sheets were foundafter the treatment with strong hydrofluoric acid confirms the formationTi3C2Tx layered sheets. The synthesized Ti3C2Tx MXene possesses excellent photocatalytic activity for the degradation of dyes MB, RhB, and mixtures of MB and RhB dyes. MB dye degraded with a degradation percentage efficiency of 99.32% in 30min, while RhB dye was degraded upto98.9% in 30min. Also, experiments were conducted for degradation ofmixture of MB and RhB dyes by UV light, and the degradationpercentage efficiency were found to be 98.9% and 99.75% for mixture of MB and RhB dyein 45min, respectively. Moreover, reaction rate constant (k) was determined for each dye of MB, RhB, and mixtures of MB and RhB and was found to be 0.0215min-1 and 0.0058min-1, and for mixtures, it was 0.0020min-1 and 0.009min-1, respectively.

Solvent-free one-step green synthesis of MXenes by “gas-phase selective etching”

Two-dimensional transition metal carbides and nitrides (MXenes) have attracted extensive attention due to their unique electronic properties and various applications for energy harvesting. However, the current synthesis procedures involve using fluoride-based aqueous solutions via reacting with Al-containing MAX phases. Besides, fluorine-free, cost-effective, and straightforward synthetic methods are rarely reported and need to be explored. Here, a solvent-free one-step gas-phase dry etching method, named “Gas-Phase Selective Etching”, was first proposed and used to etch different elements A (Al, Si, Sn, etc.) of MAX phases using the strong oxidation ability of halogens and hydrogen halides gases (Cl2, Br2, I2, HCl, HBr, and HI). The gas-phase etching can achieve a pure product of MXenes coupled with specific gas-induced functional groups. Meanwhile, MXenes powder can be directly obtained without the removal processes of etchants and by-products. Furthermore, the multilayer-MXene with -Cl functional groups (Ti3C2Cl2) has strong oxidation resistance and superior rate performance of capacitance. It provides us with an intelligent, cost-effective synthesis strategy that has a high yield and is safe, allowing for the promising mass production of MXenes.

Lightweight and robust cellulose/MXene/polyurethane composite aerogels as personal protective wearable devices for electromagnetic interference shielding

The increasing electromagnetic pollution is urgently needed as an electromagnetic interference shielding protection device for wearable devices. Two-dimensional transition metal carbides and nitrides (MXene), due to their interesting layered structure and high electrical conductivity, are ideal candidates for constructing efficient conductive networks in electromagnetic interference shielding materials. In this work, lightweight and robust cellulose/MXene/polyurethane composite aerogels were prepared by mixing cellulose nanofiber (CNF) suspensions with MXene, followed by freeze-drying and coating with polyurethane. In this process, CNF effectively assembled MXene nanosheets into a conductive network by enhancing the interactions between MXene nanosheets. The prepared aerogel exhibited the shielding effectiveness of 48.59 dB in the X-band and an electrical conductivity of 0.34 S·cm−1. Meanwhile, the composite aerogel also possessed excellent thermal insulation, infrared stealth, mechanical and hydrophobic properties, and can be used as a wearable protective device to protect the human body from injuries in different scenarios while providing electromagnetic interference shielding protection.

Highly sensitive determination of acyclovir using Ti3C2-CS-MWCNTs-COOH/GCE composite as a sensing platform

Acyclovir (Acyclovir, ACV) is an antiviral drug which, despite its favorable safety profile, can have systemic adverse effects, following improper use. This study prepared a clay-like two-dimensional transition metal carbide Ti3C2 by etching Ti3AlC2 with LiF and HCl. Carboxylated multi walled carbon nanotubes (Carboxylated multi-walled carbon nanotubes, MWCNTs-COOH) were combined with Ti3C2 using chitosan (Chitosan, CS) as solvent and ultrasonic treatment. The nanocomposite was then modified onto the surface of a glassy carbon electrode (Glassy carbon electrode, GCE) to develop an electrochemical sensor for the detection of ACV. The Ti3C2-CS-MWCNTs-COOH/GCE nanocomposite was characterized by X-ray diffractometry (X-ray diffractometry, XRD), scanning electron microscope (Scanning electron microscope，SEM), and cyclic voltammetry (Cyclic voltammetry，CV), as well as the electrochemical impedance method (Electrochemical impedance，EIS). The successful preparation of Ti3C2-CS-MWCNTs-COOH, and the good electrochemical performance of the electrode were verified. Linear scanning voltammetry (Linear scan voltammetry，LSV) was used to quantify the ACV. The linear range of the method is wider than other works (0.05 ∼ 20.0 and 20.0 ∼ 500.0 μM), with a low detection limit (0.088 μM). The sensor achieves sensitive detection of ACV and can be used for the analysis of ACV in pharmaceutical and urine dosage forms, with recoveries of 95.5∼97.6% and 95.6∼97.5%, respectively. For the first time, this sensor utilizes clay-like Ti3C2 with a larger specific surface area in combination with MWCNTs-COOH for ACV detection, which exhibits excellent immunity to interference, repeatability, reproducibility, and stability. This method provides a rapid and sensitive method for the determination of ACV, and lays foundations for developing miniaturized field rapid test detectors.

Centrifugal-Gravity-Enforced Deposition of MXene Electrodes for High-Performance and Ultrastable Microsupercapacitors.

Two-dimensional (2D) transition metal carbides, known as MXenes, have captured much attention for their excellent electrical conductivity and electrochemical capability. However, the susceptibility of MXenes to oxidation, particularly Ti3C2Tx transforming into titanium dioxide upon exposure to ambient air, hinders their utilization for extended operational life cycles. This work introduces a simple and straightforward method for producing ultrathin MXene electrode films tailored for energy storage applications, employing centrifugal-gravity force. Our approach significantly suppresses the oxidation phenomenon that arises in MXene materials and also effectively prevents the recrystallization of potentially residual LiF during the film formation. Additionally, the utilization of this MXene electrode in an all-solid-state microsupercapacitor (MSC) with an interdigitated pattern demonstrates an exceptionally improved and stable electrochemical performance. This includes a high volumetric capacitance of approximately 467 F cm-3, an energy density of around 65 mWh cm-3, and impressive long-term cycle stability, retaining about 94% capacity after 10 000 cycles. Moreover, a downsized MSC device exhibits remarkable mechanical durability, retaining over 98% capacity even when folded and sustaining stability over extended periods. Therefore, we believe that this study provides valuable insights for advancing highly integrated energy storage devices, ensuring exceptional electrochemical efficiency and prolonged functionality in diverse environments, whether ambient or humid.