2D Transition Metal Carbides Research Articles

Low-temperature carbonized biomimetic cellulose nanofiber/MXene composite membrane with excellent microwave absorption performance and tunable absorption bands

2D transition metal carbides and nitrides (MXenes) have gained much interest in microwave absorption. However, the high conductivity of MXenes results in inferior absorption performance. To solve this problem, Cellulose nanofiber (CNF) is compounded with MXenes to build membranes with biomimetic structures. CNF not only contributes to adjusting the electromagentic parameters, but also enhances the microwave attenuation and regulates the absorption band. In this work, nacre-like and loofah-like carbonized CNF/MXenes membranes were successfully prepared. The self-assembly of CNF and MXene avoids the impedance mismatch, and the biomimetic structures enhance conductive loss, polarization loss and multiple reflection. The results show that nacre-like carbonized CNF/MXene membrane (CCM) exhibits absorbing performance with the minimum reflection loss (RLmin) of −42.2 dB and the Effective absorption band (EAB) of 7.12 GHz. Meanwhile, the absorption peaks are mainly concentrated on X-band. Further, as the morphology changes to porous layers, the RLmin of loofah-like CCM increases to −63.8 dB, whose EAB is 7.32 GHz at 2.5 mm, and the main absorption peaks shift to Ku-band. Besides, the possible absorption mechanism of biomimetic composite membranes has been expounded. This work provides a versatile strategy for CNF/MXene composite membrane with biomimetic structures on excellent and tunable microwave absorption performance.

Enhanced Performance of Silicon Negative Electrodes Composited with Titanium Carbide Based MXenes for Lithium-Ion Batteries

Silicon is considered as one of the most promising candidates for the next generation negative electrode (negatrode) materials in lithium-ion batteries (LIBs) due to its high theoretical specific capacity, appropriate lithiation potential range, and fairly abundant resources. However, the practical application of silicon negatrodes is hampered by the poor cycling and rate performances resulting mainly from the huge volume change during Li+ insertion/extraction. Various composite structures have been investigated to maintain the structural integrity and improve the stability and electric conductivity of silicon-based negatrodes. Of these, 2D transition-metal carbides, also known as MXenes (e.g., Ti3C2Tx), have become increasingly attractive for energy storage applications because of their excellent electric, electrochemical and mechanical properties and potential uses as the matrix for construction of 3D networks with larger buffering spaces and more effective charge carrier conduction in silicon-based negatrodes. This article reviews specifically composite negatrodes of silicon with titanium-carbide-based MXenes for LIBs from the materials perspective. The structures design, preparation method, interface control, and their effects on electrochemical performances are comprehensively elaborated on. It is shown that the recent development of Si/MXene-based negatrodes presents great potential for future applications.

Self-assembly and in-situ characterization of Ti3C2Tx in Al: A step toward additive manufacturing of MXene-metal composites

Two-dimensional (2D) transition metal carbides, known as MXenes, have grown in research interest since 2011 partly due to their impressive high electrical conductivity, stiff mechanical properties, and abundant chemically-active surface groups. These key features of MXenes make them attractive candidates for uniform coverage of metal powders for additive manufacturing of multi-functional metal composites. In this study, we report on a tunable self-assembly process of nanometer-thick 2D MXene flakes on micron-size Al particles using 1–10 wt% of single-to-few and multi-layer Ti3C2Tx MXene. In addition, we discuss the characterization of these composites using 2D x-ray diffraction (XRD2) for identification of the characteristic Ti3C2Tx diffraction peaks. Lastly, we use in-situ XRD2 paired with Vickers hardness and scanning electron microscopy/energy dispersive x-ray spectroscopy methods to understand the effect of sintering on the Ti3C2Tx morphology and the resultant mechanical properties of the bulk composite. This study aims to assist future advances in additive manufacturing of MXene-metal composites for an array of multi-functional applications.

Patterning of Wafer-Scale MXene Films for High-Performance Image Sensor Arrays.

As a rapidly growing family of 2D transition metal carbides and nitrides, MXenes are recognized as promising materials for the development of future electronics and optoelectronics. So far, the reported patterning methods for MXene films lack efficiency, resolution, and compatibility, resulting in limited device integration and performance. Here, a high-performance MXene image sensor array fabricated by a wafer-scale combination patterning method of an MXene film is reported. This method combines MXene centrifugation, spin-coating, photolithography, and dry-etching and is highly compatible with mainstream semiconductor processing, with a resolution up to 2µm, which is at least 100 times higher than other large-area patterning methods reported previously. As a result, a high-density integrated array of 1024-pixel Ti3 C2 Tx /Si photodetectors with a detectivity of 7.73 × 1014 Jones and a light-dark current ratio (Ilight /Idark ) of 6.22 × 106 , which is the ultrahigh value among all reported MXene-based photodetectors, is fabricated. This patterning technique paves a way for large-scale high-performance MXetronics compatible with mainstream semiconductor processes.

Unveiling the promotion of intermediates transport kinetics on the N/S co-doping 3D structure titanium carbide aerogel for high-performance supercapacitors

Two-dimensional (2D) transition metal carbides (MXene) have shown great advantages as electrode materials in the new generation of energy storage, especially in supercapacitors. However, the inherent low specific capacitance and restacking layers of nanosheets that occur during electrode preparation further reduce the electrochemical performance of the materials. Based on this, we design a N, S co-doping electrode with a three-dimensional (3D) structure, which not only improves the specific capacitance through fundamentally modifying the electronic structure of the electrode materials, but also effectively improves the rate performance of the electrode by preventing the restacking of 2D materials. The N, S co-doping 3D architecture Ti3C2Tx electrode (TC/NS-3D) exhibits an excellent capacitance value of 440 F g−1 at 5 mV s−1 and 64% capacitance retention rate at a high scan rate of 1000 mV s−1 in 3 mol L−1 H2SO4 electrolyte. The TC/NS-3D electrode also shows excellent capacitance retention of 97.2% after the 10,000 cycles stability test. The density functional theory (DFT) analysis reveals the enhanced performance is attributed to accelerated intermediates transport kinetics promoted by 3D structure engineering and N, S co-doping for Ti3C2Tx. This study is promising in designing heteroatomic doping 3D structure MXene-based materials for electrochemical energy storage systems.

Dielectric properties and energy storage performance of PVDF-based composites with MoS2@MXene nanofiller

Hybrid nanofillers designed for polymer dielectric nanocomposites are expected to obtain excellent dielectric energy storage performance by virtue of different morphologies and electrical properties. In this work, the 2D/2D heterostructures of 2D MoS2 grown on the surface of 2D transition metal carbide Ti3C2 MXene (MoS2@MXene) have been successfully obtained through hydrothermal reaction. MoS2@MXene was incorporated into poly (vinylidene fluoride) (PVDF) to form the PVDF based dielectric composites (MoS2@MXene/PVDF) through solution casting method. The composite with 3.47 wt% MoS2@MXene is very flexible with an elastic modulus of 385 MPa, which is not much different with pure PVDF (357 MPa). The maximum electric displacement at room temperature and an electric field of 400 MV/m is 10.96 μC/cm2, moreover the discharged energy density reaches 17.22 J/cm3, which is nearly 4.5 times that of pure PVDF (3.83 J/cm3 at the maximum electric field of 250 MV/m). The dielectric constant of 3.47 wt% MoS2@MXene/PVDF at room temperature and 103 Hz is 24.3, and the loss is only 0.02. Even though the filler content is increased to 12.51 wt%, the loss is only 0.06, and the dielectric constant of the composite film can reach 145.2. Compared with the blend of PVDF and MXene, the dielectric constant of MXene@MoS2/PVDF shows more excellent frequency stability and lower dielectric loss.

Recent Advances in Oxidation Stable Chemistry of 2D MXenes.

As an emerging star of 2D nanomaterials, 2D transition metal carbides and nitrides, named MXenes, present a large potential in various research areas owing to their intrinsic multilayer structure and intriguing physico-chemical properties. However, the fabrication and application of functional MXene-based devices still remain challenging as they are prone to oxidative degradation under ambient environment. Within this review, the preparation methods of MXenes focusing on the recent investigations on their thermal structure-stability relationships in inert, oxidizing, and aqueous environments are systematically introduced. Moreover, the key factors that affect the oxidation of MXenes, such as, atmosphere, temperature, composition, microstructure, and aqueous environment, are reviewed. Based on different scenarios, strategies for avoiding or delaying the oxidation of MXenes are proposed to encourage the utilization of MXenes in complicated environments, especially at high temperature. Furthermore, the chemistry of MXene-derived oxides is analyzed, which can offer perspectives on the further design and fabrication of novel 2D composites with the unique structures of MXenes being preserved.

Facile preparation and characterization of MXene@Platinum nanocomposite for energy conversion applications

The 2D transition metal carbide, MXene (MX - TixCxTx) and MX@Pt nanocomposites was prepared from MAX (Ti3AlC2) precursor. The effective nanocomposite (MXene/Pt) photocatalysts are prepared by facile water bath sonication and CVD tubular furnace thermal annealing treatment at 600 °C. The successfully prepared MAX into MXene (MX) flakes are also compared to structural conformation of MX@Pt nanocomposites through XRD results and revealed good crystalline diffracted peaks. The micro-RAMAN results explored with excelent connection of 106.49 and 612.78 cm−1. The FT-IR substantiation for Ti-C and Ti-O-C stretching for MXene (TixCxTx) functional groups confirm the MAX, MX, MX@Pt materials formation. The surface FE-SEM morphology explored MXene few-layer sheets with ‘Pt’ decorated (MX@Pt) nanocomposites. Further, FE-SEM with EDAX elemental characterization system confirm materials atomic percentage as ‘Ti’– 48.36 at. %, ‘C”– 48.63 at. % and platinum ‘Pt’– 3.01 at. %. Finally, MX@Pt nanocomposites explored to HER studies, which exhibited 165 mV to attain 10 mA/cm2 and it exhibited 477 mV overpotential to reach 100 mA/cm2. MX@Pt nanocomposites revealed for H2 and HER activity applications will demonstrate future potential H2 productions and water splitting applications.

Effect of vacancies on the electrochemical behavior of Mo-based MXenes in aqueous supercapacitors

i-MXenes, a new family of 2D transition metal carbides with in-plane ordered vacancies, have shown great potential in aqueous supercapacitor (SC) applications due to their high volumetric capacitances and energy densities. However, how vacancies affect their electrochemical performance, in general, and their self-discharge (SD) behavior in particular, remains unexplored. Herein, we compare the electrochemical performance of vacancy-rich, ordered Mo1.33CTzi-MXene to that of Mo2CTz (with much less vacancies) in a 1 M sulfuric acid (H2SO4) or 15 M of lithium bromide (LiBr) electrolyte. The Mo1.33CTz exhibits higher volumetric capacitances and energy densities, but at the cost of a higher SD rate. Specifically, the Mo1.33CTz symmetric SCs deliver an energy density as high as 25.4 mWh cm−3 at 152.4 mW cm−3, with 65.4% voltage retention after 10 h in 15 M LiBr. In comparison, the Mo2CTz symmetric SCs have a maximum energy density of 20.8 mWh cm−3 at 124.9 mW cm−3, with 73.1% voltage retention after 10 h in the same electrolyte. The SD rates in the H2SO4 electrolyte are quite rapid.

A perspective on high‐entropy two‐dimensional materials

AbstractIn past decades, high‐entropy (HE) materials, containing five or more elements with approximately equal atomic ratio, are extensively investigated due to their desirable properties in a series of applications. Recently, HE two‐dimensional (2D) materials have become promising materials, which not only endow the advantages from their bulk form but also exhibit unusual properties due to their 2D features. So far, the HE 2D transition metal carbides (MXenes), dichalcogenides (TMDs), hydrotalcites (LDHs), and oxides have been successfully synthesized and performed well in different electrochemical reactions, which is originated from the synergistic effect of multicomponents and atomic thin characteristics. Here, the challenges on processing, characterization, and property predictions of HE 2D materials are emphasized. Finally, viable strategies, advanced processing, fundamental understanding, in‐depth characterization of new HE 2D materials are proposed.

Durable and highly sensitive flexible sensors for wearable electronic devices with PDMS-MXene/TPU composite films

MXenes, as two-dimensional (2D) transition metal carbides, carbonitrides, and nitrides, have very excellent electrical properties and surface activity and are increasingly used in supercapacitors, batteries, electromagnetic interference shielding, and composite materials. Still, the poor stability of MXene when exposed to aqueous oxygen and the poor ability to interact with the polymer matrix have become important factors limiting its’ practical applications. To enhance stability, highly conductive and stretchable Ti 3 C 2 MXene/TPU sensing elements were prepared by a simple spraying process using thermoplastic polyurethane (TPU) as a substrate, and the sensing elements were encapsulated by polydimethylsiloxane (PDMS) to obtain MXene-TPU/PDMS constructed flexible strain sensors with excellent performance. This strain sensor features low detection limits (less than 0.005%, 0.5 μm), a wide sensing range (0–90%), a short response time (120.1 ms), and excellent durability (>3000 cycles). This strain sensor can be applied to a range of applications such as health detection, motion signals, detection of robot movements, and wearable electronic devices.

Deicing coatings go transparent

A new transparent deicing coating that can also clean itself could be a boon for solar panels, windows, and windshields ( Adv. Mater. 2021, DOI: 10.1002/adma.202108232 ). Preventing ice buildup on car windshields and aircraft today requires spraying the surfaces with glycol-based antifreeze or deicing fluids. For a simpler, more ecofriendly alternative , researchers are developing anti-ice coatings . These include superhydrophic or super-slippery surfaces that make water roll or slip off to delay freezing. Some groups have also made surfaces that heat up electrically or by absorbing sunlight to melt ice. Solar heating materials are the most economical and environmentally friendly method to combat ice, says Xiaokong Liu, a chemist at Jilin University. But light-absorbing materials generally tend to be dark. Liu and his colleagues made see-through coatings with MXenes , a class of 2D transition-metal carbides and nitrides. They deposited alternating nanosheets of the negatively charged titanium carbide

Microscopic understanding of exceptional orientation-dependent tensile and fracture responses of two-dimensional transition-metal carbides

Two-dimensional (2D) materials have exceptional mechanical properties that are absent in conventional bulk materials due to their ultra-thin structure with ultra-high surface-to-volume ratio. Despite their great potential both for basic research and applications, however, deep understanding of fundamentally important orientation-dependent mechanical responses of 2D materials have rarely been achieved. In this work, for the first time, we investigate the tensile mechanical response of 2D transition-metal carbides (MXenes) as gradually varying tensile direction by using reactive molecular dynamics simulations. Despite its highly bonded multi-atom-thick structure, MXene proves significantly stretchable (11–17%) for all directions with isotropic stiffness desirable for flexible/wearable applications, while exhibiting unusual characteristic fracture anisotropy. Noticeably, these mechanical features remained qualitatively the same regardless of presence/absence of surface termination. We discover that MXene has always fractured into zigzag-atomic edged fragments regardless of tensile direction and/or surface termination. We reveal the detailed fracture mechanism and propose its generalization to other hexagonal 2D materials with validation for both pristine and surface-hydrogenated graphene nanosheets. Based on these findings, we finally present a physically robust, computationally efficient framework for fast and reliable prediction of MXenes’ unique fracture anisotropy, showing excellent agreement with time-consuming simulation results and suggesting broad applicability to 2D material mechanics.

Mechanically robust and multifunctional polyimide/MXene composite aerogel for smart fire protection

Multifunctional smart fire-protection aerogels are urgently needed to meet the requirement of the Internet of Everything era. Herein, we fabricated a mechanically robust and high fire-safe polyimide/MXene composite aerogel (denoted as PI@MXene) with sensitive temperature-sensing and fire-warning capability. Thanks to the unique thermoelectric effect and high electrical conductivity of the 2D transition metal carbide (MXene) nanosheet, PI@MXene exhibited a linear relationship between the thermoelectric voltage and the temperature difference, showing sensitive temperature-sensing capability. When being burned, it could repeatedly trigger the fire-warning system in less than 5 s. More importantly, owing to the lamellar barrier and skeleton supporting effect of the MXene nanosheets, PI@MXene exhibited excellent flame retardancy, which self-extinguished within 1 s after exposing to a flame for 60 s and whose peak heat release rate was significantly decreased by 78% compared with PI aerogel. Besides, PI@MXene showed impressive thermal insulation, outstanding thermostability and durable piezoresistive sensing. This work provides a novel strategy to fabricate next-generation multifunctional fireproof aerogel, showing promising applications in intelligent robots, aerospace, and railway transportation.

Microstructure and tribological behavior of Ti3C2Tx MXene reinforced chemically bonded silicate ceramic coatings

MXenes – In recent decades, great attention has been paid to the fast-growing two-dimensional (2D) transition metal carbides and nitrides, in terms of their prominent mechanical and electrical properties. The tribological essence of MXene has not yet been entirely investigated, although researches on MXene were conducted in all aspects of its applications. Hence, a newly compound 2D MXene (Ti 3 C 2 T x ) is exploited to reinforce the wear resistance of the chemically bonded silicate ceramic coatings, which are utilized to protect component surfaces under severe conditions. The structural features, hardness, and tribological behaviors of the targeted coatings are investigated and analyzed. Results show that the micro-hardness of the coatings increases to 156.9 HV 0.5 when added 1.2 wt% MXene. The increment of microhardness extraordinarily reaches 33.3%, compared with the original. The coating with 1.2 wt% MXene also indicates a 31.6% decrement of the coefficient of friction (COF) and a 73% reduction of the wear rate respectively. Furthermore, fatigue is found to be the main reason of the wear mechanism, through exploring the surface morphologies of wear traces and counterpart balls.

Microwave-Pulse Sugar-Blowing Assisted Synthesis of 2d Transition Metal Carbides for Sustainable Hydrogen Evolution

Microwave-Pulse Sugar-Blowing Assisted Synthesis of 2d Transition Metal Carbides for Sustainable Hydrogen Evolution

A lithium-MXene composite anode with high specific capacity and low interfacial resistance for solid-state batteries

MXenes, a family of two-dimensional (2D) transition metal carbides, nitrides and carbonitrides, offer great potential for the rational design of many new composites due to their attractive properties and surface terminations. In this study, we present a new lithium-MXene composite (Li-MXene) anode design that substantially reduces interfacial Li ion transport resistance between Li metal anode and garnet solid-state electrolyte. When evaluated as electrodes in Li-MXene|garnet|Li-MXene symmetric cells, the interfacial resistance is negligible (5 Ω•cm2). By contrast, the pure Li-based counterpart shows poor contact with garnet, and thus induces a much larger interfacial resistance of 1291 Ω•cm2. Simultaneously, thanks to the existence of fluorinated functionalized surfaces on MXene, LiF was in-situ formed at the Li-MXene/garnet interface, which effectively isolated electron transport and suppressed the formation of dendritic Li. A high critical current density of up to 1.5 mA/cm2 has been enabled. These findings suggest the possibility of tuning the properties of Li metal anode by altering additives with different functional groups and also motivate future work employing MXene as additives towards new composites.

Sensitive electrochemiluminescence biosensing of polynucleotide kinase using the versatility of two-dimensional Ti3C2TX MXene nanomaterials

Electrochemiluminescence (ECL) is a powerful readout method for the development of (bio)sensors, whose performances depend on the electrode materials and the architecture of its surface. Herein, we demonstrate that the precise control of the sensing interface using the versatility of two-dimensional (2D) transition metal carbides (Ti3C2TX MXene) leads to the enhancement of the ECL signal. This electrode material, which exhibits remarkable structural and electrochemical properties was decorated by the in situ formation of gold nanoparticles (AuNPs) owing to the Ti reducibility. Then, a large amount of the luminophore, Ru(bpy)32+, was immobilized on Ti3C2TX MXene thanks to its unique negative charge and large specific surface area to obtain Ru–Ti3C2TX-AuNPs. The presented approach exploits the high catalytic activity and excellent conductivity of this 2D nanomaterial as illustrated by the enhanced ECL emission performance of the Ru–Ti3C2TX-AuNPs nanoprobes. Finally, DNA phosphorylated with polynucleotide kinase (PNK) was recognized efficiently by the chelation between Ti and phosphate group. A highly sensitive and selective ECL biosensor was developed for the detection of PNK and the screening of its inhibitors. A lower detection limit of 0.0002 U mL−1 and wide linear relationship ranged from 0.002 to 10 U mL−1 were obtained. Furthermore, the practicality of our method was tested in MCF-7 cell lysate, which opens enticing perspectives for future applications of Ti3C2TX materials in the ECL bioanalysis field.

MXsorption of mercury: Exceptional reductive behavior of titanium carbide/carbonitride MXenes

Two-dimensional (2D) transition metal carbides and nitrides (MXenes) have drawn considerable attention for application in the field of environmental remediation. In this study, we report the simultaneous reductive–adsorption behavior of Ti3CNTx for toxic metal ion Hg2+ ion in the aqueous phase. 2D Ti3CNTx and Ti3C2Tx MXene nanosheets were synthesized by exfoliation of Ti3AlCN and Ti3AlC2 MAX phases, respectively. Various characteristics analysis confirmed the successful fabrication of MAX phases and their exfoliation into MXenes. The fabricated MXene nanosheets were used to investigate their Hg2+ removal, Hg2+ intercalation, and surface interaction mechanism efficiencies. Both MXenes were found to adsorb and reduce a large amount of Hg2+. Analytical techniques such as X-ray powder diffraction, field emission transmission electron microscopy, zeta-potential analyses, and X-ray photoelectron spectroscopy were used to investigate the material characteristics and structural changes after uptake of Hg2+. The quantitative investigation confirmed the interaction of bimetal and hydroxyl groups with Hg2+ using electrostatic interactions and adsorption-coupled reduction. In addition, both MXenes exhibited extraordinary Hg ion removal capabilities in terms of fast kinetics with an excellent distribution coefficient (KdHg) up to 1.36 × 10+9. Based on batch adsorption results, Ti3C2Tx and Ti3CNTx exhibited removal capacities of 5473.13 and 4606.04 mg/g, respectively, for Hg2+, which are higher than those of previous Hg adsorbents.

Plate-barrier architecture of rGO-TiO2 derived from MXene for constructing well-aligned polymer nanocomposites with excellent dielectric performance

Dielectric polymers are playing increasingly important roles in advanced electronics and electric power systems, because of their high dielectric strength, stability, and lightweight. However, the relatively low intrinsic dielectric constant of dielectric polymers hinders their further applications. Herein, dielectric polymer composites were fabricated by blending with plate-barrier architecture fillers, which are comprised of reduced graphene oxide (rGO) and intercalated titanium dioxide (TiO2) cubes. TiO2 cubes are homogeneously and controllably integrated onto rGO nanosheets utilizing 2D transition metal carbides (MXene) by means of shape match. TiO2 cubes could serve as joints to anchor rGO nanosheets for more effective polarization, and as barriers to impede the conductive contact of rGO nanosheets. In the nanocomposites, rGO nanosheets possess high alignment and overlap area resorting to the anchoring effect of TiO2, which increases the micro-capacitors in series that greatly enhance the dielectric constant. Therefore, it is investigated that the nanocomposites exhibit a high dielectric constant (211) and ultralow dielectric loss (0.104). Moreover, the enhancement mechanism of the micro-capacitors was also revealed by the finite element simulation. This contribution provides a novel strategy to fabricate well-aligned nanocomposites that are promising in electronics flexible materials.