2D Ti3C2Tx Research Articles

Amine-Assisted Delaminated 2D Ti3C2Tx MXenes for High Specific Capacitance in Neutral Aqueous Electrolytes.

Electrochemical capacitors using neutral aqueous electrolytes are safer and cheaper and allow diverse current collectors compared with the counterparts using organic or acidic/alkaline electrolytes. Two-dimensional (2D) MXenes have been demonstrated as the high-capacitive materials with high rate performance. However, MXene electrodes often exhibit a limited capacitance in neutral electrolytes, where the reversible electrochemical reactions rely greatly on the structural and surface properties of MXenes depending on their synthesis methods. Herein, a simple and highly efficient strategy, which combines HF etching of Ti3AlC2 powder and subsequent amine-assisted delamination at a low temperature, is developed to synthesize 2D Ti3C2Tx MXenes. The comprehensive results demonstrate that the enlarged interlayer spacing and the presence of more -O-containing functional groups synergistically contribute to the improvement of capacitive performance in neutral electrolytes. The 2D Ti3C2Tx MXenes show excellent electrochemical performance in various neutral electrolytes, and a high specific gravimetric capacitance of 149.8 F/g is achieved in 1.0 M Li2SO4. Furthermore, the flexible solid-state supercapacitors (SCs) with a neutral PVA/LiCl gel electrolyte possess a superior areal capacitance (163.1 mF/cm2) and high energy density (17.6 μWh/cm2 at 0.07 mW/cm2), together with high user safety. This work provides a promising guideline of synthesis strategy for high-capacitive MXenes used in neutral electrolytes, which may promote the development of safe and flexible power sources with a high energy density.

Ti3 C2 Tx MXene Conductive Layers Supported Bio-Derived Fex -1 Sex /MXene/Carbonaceous Nanoribbons for High-Performance Half/Full Sodium-Ion and Potassium-Ion Batteries.

Owing to their cost-effectiveness and high energy density, sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) are becoming the leading candidates for the next-generation energy-storage devices replacing lithium-ion batteries. In this work, a novel Fex -1 Sex heterostructure is prepared on fungus-derived carbon matrix encapsulated by 2D Ti3 C2 Tx MXene highly conductive layers, which exhibits high specific sodium ion (Na+ ) and potassium ion (K+ ) storage capacities of 610.9 and 449.3mAhg-1 at a current density of 0.1Ag-1 , respectively, and excellent capacity retention at high charge-discharge rates. MXene acts as conductive layers to prevent the restacking and aggregation of Fex -1 Sex sheets on fungus-derived carbonaceous nanoribbons, while the natural fungus functions as natural nitrogen/carbon source to provide bionic nanofiber network structural skeleton, providing additional accessible pathways for the high-rate ion transport and satisfying surface-driven contribution ratios at high sweep rates for both Na/K ions storages. In addition, in situ synchrotron diffraction and ex situ X-ray photoelectron spectroscopy measurements are performed to reveal the mechanisms of storage and de-/alloying conversion process of Na+ in the Fex -1 Sex /MXene/carbonaceous nanoribbon heterostructure. As a result, the assembled Na/K full cells containing MXene-supported Fex -1 Sex @carbonaceous anodes possess stable large-ion storage capabilities.

Ultralow Ti3C2TX doping polysulfate membrane for high ultrafiltration performance

Incorporating hydrophilic nanomaterial fillers into a polymeric matrix enables a high-performance ultrafiltration membrane. 2D Ti3C2TX nanosheets are promising candidates due to their hydrophilic nature and good dispersion ability in the organic solvent. In this study, novel polysulfate (PSE)/Ti3C2TX ultrafiltration membranes were prepared by non-solvent induced phase separation (NIPS) method. The phase inversion process of the PSE/Ti3C2TX casting membranes was visualized. Ti3C2TX nanosheets could tune the phase inversion process effectively and promote the phase inversion speed with an ultralow content of 0.05 wt%. As a result, the hydrophilic property and porosity of PSE/Ti3C2TX membrane could be improved. The skin layer thickness was significantly reduced, resulting in saliently ultrafiltration performance, i.e., a pure water flux (PWF) of 685 L*m−2*h−1 (LMH) with a bovine serum albumin (BSA) rejection of 97%. The proposed ultralow Ti3C2TX doping in the casting solutions method offers a versatile platform to manipulate the phase inversion progress during the industrially NIPS process, and enhanced the separation performance of ultrafiltration membranes.

Rational design of A-CNTs/KxMnO2 and Ti3C2Tx/MoO3 free-standing hybrid films for flexible asymmetric supercapacitor

A flexible quasi-solid-state asymmetric supercapacitor (ASC) with high energy density has been designed and fabricated, exploiting a self-assembled Ti3C2Tx/MoO3 composite as the negative electrode and interpenetrating A-CNTs/KxMnO2 nanowires networks as the positive electrode. The negative electrode exhibits excellent capacity (371 C g−1 or 715 C cm−3 at 1 A g−1) and cycle stability (89.5% after 6000 cycles), which is attributed to the synergistic effect of high conductive two-dimensional (2D) Ti3C2Tx nanosheets and high pseudocapacitive MoO3 nanobelts because Ti3C2Tx can effectively alleviate the volume effect of MoO3 during the charge/discharge process. The positive electrode shows improved rate capability and capacitance with K+ ions pre-intercalation, which effectively enlarges and stabilizes the diffusion channel of the electrolyte cations. The A-CNTs/KxMnO2//Ti3C2Tx/MoO3 ASC exhibits a high capacitance of 65.5 F g−1 (107.1 F cm−3) and a high energy density of 36.4 Wh kg−1 (59.5 Wh L−1) at a power density of 863.5 W kg−1 (1410.9 W L-1) with expanded operation voltage up to 2 V in the aqueous electrolyte, showing excellent cycle stability with capacitance retention of 91.7% after 6000 charge/discharge cycles. This work provides a simple but effective strategy for the development of the next-generation flexible supercapacitors with high energy and power densities.

2D titanium and vanadium carbide MXene heterostructures for electrochemical energy storage

Two-dimensional (2D) heterostructured electrodes built from vertical stacking of different 2D materials are among the most promising electrode architectures for electrochemical energy storage devices. These materials offer interesting opportunities for energy storage applications such as versatility in the structural design of electrode, and the possibility to integrate individual 2D building blocks with different properties into heterostructures. These features can potentially enable new materials with improved or new electrochemical features. Here, we report on large-scale liquid phase self-assembly of 2D heterostructures built from two different 2D transition metal carbides (MXenes), Ti3C2Tx and V2CTx. A cation-driven self-assembly process was used to assemble the negatively-charged flakes of the two MXenes into heterolayered flakes. The freestanding and binder-free MXene heterostructure films could deliver a high volumetric capacitance of ~1473 F cm−3 and showed no capacitance loss after 50,000 charge-discharge cycles in 3 M H2SO4 electrolyte. Due to coupling of redox reactions of Ti3C2Tx and V2CTx, the heterostructure electrodes showed a nearly constant current over their entire potential window, which is reminiscent of traditional pseudocapacitive materials. This electrochemical behavior differs from individual MXene electrodes or most other emerging pseudocapacitive materials whose maximum performance is usually achieved in a narrow potential range.

A MOFs-derived 3D superstructure nanocomposite as excellent microwave absorber

Developing an expandable microstructure method to acquire high-performance microwave absorbers is an effective strategy to prevent electromagnetic wave radiation pollution. In this study, a three-dimensional (3D) conductive network is constructed using 1D carbon nanotubes (CNTs) derived from Ni (hollow and solid microsphere structure) metal–organic-frameworks (MOFs) and 2D Ti3C2Tx MXene simultaneously to form a superstructure composite material. The results of the experiment and analysis confirm the successful synthesis of 3D superstructure composites with excellent microwave absorption (MA) properties. The optimal reflection loss (RL) is − 57.78 dB with a thickness of 1.49 mm at 8.4 GHz, and the maximum effective absorption bandwidth is 3.44 GHz for a thickness of 0.8 mm. In the unique 3D superstructure, microwave attenuation capacity and impedance matching are optimized under the synergistic effect of multiple resonances and polarization relaxation. Simultaneously, adjustable and efficient MA between the C and X bands is achieved by modulating the loading of the Ni particle hybrid. It is anticipated that this superstructure composite material can be used for a new generation of microwave absorbers.

Highly Efficient Adsorption of Bilirubin by Ti3 C2 Tx MXene.

We discovered that the 2D Ti3 C2 Tx MXene sheet displays an ultra-high removal capability for bilirubin (BR). In particular, MXene shows 47.6 times higher removal efficiency over traditional activated carbon absorbents. The effect of MXene on the removal rate of BR in BR solution containing different concentrations of bovine serum albumin (BSA) was studied. The adsorption capacity of BSA for BR at high concentration of 5 g L-1 was about 85% of the best adsorption capacity. The MXene before and after adsorption was characterized by SEM, FT-IR and XPS. Furthermore, MXene beads were prepared, and the hemoperfusion simulation experiment was carried out. The results show that the adsorption capacity of MXene for bilirubin can reach 1192.9 mg g-1 . This study suggests that MXene may be promising in the treatment of hyperbilirubinemia.

Boosting Photocatalytic Activity and Stability of Lead-Free Cs3Bi2Br9 Perovskite Nanocrystals via In Situ Growth on Monolayer 2D Ti3C2Tx MXene for C-H Bond Oxidation.

Light-driven selective oxidation of saturated C-H bonds with molecular oxygen, as an alternative to conventional thermochemical catalysis, allows a sustainable and eco-friendly manner to convert solar energy into highly value-added oxygenates. However, the photocatalytic oxidation of hydrocarbons still remains a great challenge owing to the low efficiency in the separation and transfer of photogenerated charge of the currently available photocatalytic materials. Herein, we report a novel perovskite-based heterostructure photocatalyst, in which ligand- and lead-free all-inorganic perovskite Cs3Bi2Br9 nanocrystals (NCs) with uniform crystal size and high crystallinity were homogeneously distributed on the surface of ultrathin two-dimensional (2D) monolayer Ti3C2Tx MXene nanosheets in an in situ growth manner. The resultant heterostructure featured with intimate interface between Cs3Bi2Br9 NCs and Ti3C2Tx MXene and strong visible-light adsorption not only exhibits significant enhancement in the performance of photocatalytic oxidation of challenging aromatic and aliphatic alkanes under visible-light irradiation but also greatly improves the stability of Cs3Bi2Br9 NCs under a reaction environment. Comprehensive characterizations reveal that the formation of an intimate interface between Cs3Bi2Br9 NCs and highly conductive ultrathin 2D Ti3C2Tx MXene nanosheets via strong interaction markedly accelerates the separation and transfer efficiency of photogenerated electron-hole pairs and simultaneously suppresses their recombination, resulting in improved utilization of the excited charges, which account for the highly enhanced photocatalytic performance.

Interfacial piezoelectric polarization locking in printable Ti3C2Tx MXene-fluoropolymer composites

Piezoelectric fluoropolymers convert mechanical energy to electricity and are ideal for sustainably providing power to electronic devices. To convert mechanical energy, a net polarization must be induced in the fluoropolymer, which is currently achieved via an energy-intensive electrical poling process. Eliminating this process will enable the low-energy production of efficient energy harvesters. Here, by combining molecular dynamics simulations, piezoresponse force microscopy, and electrodynamic measurements, we reveal a hitherto unseen polarization locking phenomena of poly(vinylidene fluoride–co–trifluoroethylene) (PVDF-TrFE) perpendicular to the basal plane of two-dimensional (2D) Ti3C2Tx MXene nanosheets. This polarization locking, driven by strong electrostatic interactions enabled exceptional energy harvesting performance, with a measured piezoelectric charge coefficient, d33, of −52.0 picocoulombs per newton, significantly higher than electrically poled PVDF-TrFE (approximately −38 picocoulombs per newton). This study provides a new fundamental and low-energy input mechanism of poling fluoropolymers, which enables new levels of performance in electromechanical technologies.

Hetero-Dimensional 2D Ti3C2Tx MXene and 1D Graphene Nanoribbon Hybrids for Machine Learning-Assisted Pressure Sensors.

Hybridization of low-dimensional components with diverse geometrical dimensions should offer an opportunity for the discovery of synergistic nanocomposite structures. In this regard, how to establish a reliable interfacial interaction is the key requirement for the successful integration of geometrically different components. Here, we present 1D/2D heterodimensional hybrids via dopant induced hybridization of 2D Ti3C2Tx MXene with 1D nitrogen-doped graphene nanoribbon. Edge abundant nanoribbon structures allow a high level nitrogen doping (∼6.8 at%), desirable for the strong coordination interaction with Ti3C2Tx MXene surface. For piezoresistive pressure sensor application, strong adhesion between the conductive layers and at the conductive layer/elastomer interface significantly diminishes the sensing hysteresis down to 1.33% and enhances the sensing stability up to 10 000 cycles at high pressure (100 kPa). Moreover, large-area pressure sensor array reveals a high potential for smart seat cushion-based posture monitoring application with high accuracy (>95%) by exploiting machine learning algorithm.

Lysozyme Adsorption on Different Functionalized MXenes: A Multiscale Simulation Study.

Recently, MXenes, due to their abundant advantages, have been widely applied in energy storage, separation, catalysis, biosensing, et al. In this study, parallel tempering Monte Carlo and molecular dynamics methods were performed to investigate lysozyme adsorption on different functionalized Ti3C2Tx (-O, -OH, and -F). The simulation results show that lysozyme can adsorb effectively on Ti3C2Tx surfaces, and the order of interaction strength is Ti3C2O2 > Ti3C2F2 > Ti3C2(OH)2. Electrostatics together with van der Waals interactions control protein adsorption. The orientation distributions of lysozyme adsorbed on the Ti3C2O2 and Ti3C2F2 surfaces are more concentrated than that on the Ti3C2(OH)2 surface. During adsorption, the conformation of lysozyme remains stable, suggesting the good biocompatibility of Ti3C2Tx. Besides, the distribution of the interfacial water layer on the Ti3C2Tx surface has a certain impact on protein adsorption. This study provides theoretical insights for understanding the biocompatibility of 2D Ti3C2Tx materials and may help us evaluate the engineering of their surfaces for future biorelated applications.

Ultrahigh rate capability of 1D/2D polyaniline/titanium carbide (MXene) nanohybrid for advanced asymmetric supercapacitors

High energy density and enhanced rate capability are highly sought-after for supercapacitors in today’s mobile world. In this work, polyaniline/titanium carbide (MXene) (PANI/Ti3C2Tx) nanohybrid is synthesized through a facile and cost-effective self-assembly of one-dimensional (1D) PANI nanofibers and two-dimensional (2D) Ti3C2Tx nanosheets. PANI/Ti3C2Tx delivers greatly improved specific capacitance, ultrahigh rate capability (67% capacitance retention from 1 to 100 A·g−1) as well as good cycle stability. Electrochemical kinetic analysis reveals that PANI/Ti3C2Tx is featured with surface capacitance-dominated process and has a quasi-reversible kinetics at high scan rates, giving rise to an ultrahigh rate capability. By using PANI/Ti3C2Tx as positive electrode, an 1.8 V aqueous asymmetric supercapacitor (ASC) is successfully assembled, showing a maximum energy density of 50.8 Wh·kg−1 (at 0.9 kW·kg−1) and a power density of 18 kW·kg−1 (at 26 Wh·kg−1). Moreover, an 3.0 V organic ASC is also elaborately fabricated by using PANI/Ti3C2Tx, achieving an ultrahigh energy density of 67.2 Wh·kg−1 (at 1.5 kW·kg−1) and a power density of 30 kW·kg−1 (at 26.8 Wh·kg−1). The present work not only improves fundamental understanding of the structure-property relationship towards ultrahigh rate capability electrode materials, but also provides valuable guideline for the rational design of high-performance energy storage devices with both high energy and power densities.

Enhanced visible-light-induced photocatalytic NOx degradation over (Ti,C)-BiOBr/Ti3C2Tx MXene nanocomposites: Role of Ti and C doping

NOx gas pollutants have induced continuous and massive damage to our health and environment. Photocatalysts are regarded as an efficient approach for NOx degradation. Various strategies have been devoted to optimizing photocatalyst performance. In this work, a bismuth oxybromide (BiOBr) photocatalyst was successfully combined with 2D Ti3C2Tx MXene by the solvothermal treatment. It is also found that partial decomposition of Ti3C2Tx has led the in situ doping sources for BiOBr/Ti3C2Tx nanocomposite. The photocatalytic NOx purification activity of the constructed (Ti, C) co-doped BiOBr/Ti3C2Tx nanocomposites was evaluated under light illumination. The results showed that up to 61% of NOx gas has been decontaminated as short as 10 min, exceeding the pristine BiOBr and P25 titania photocatalysts. Stable performance was also achieved after several cycles, which makes (Ti,C)-BiOBr/Ti3C2Tx nanocomposites a great promise for the long term and repeated utilization. The present strategy enhanced the photoinduced electron-hole separation and transfer of the heterostructured (Ti,C)-BiOBr/Ti3C2Tx. The match band structure configuration between (Ti,C)-BiOBr and Ti3C2Tx MXene and the synergistic process between photogenerated charge carrier transfer and intermediate Ti and C levels is discussed to explain the improved photocatalytic mechanism.

Assembly of Nanofluidic MXene Fibers with Enhanced Ionic Transport and Capacitive Charge Storage by Flake Orientation.

MXenes are an emerging class of highly conductive two-dimensional (2D) materials with electrochemical storage features. Oriented macroscopic Ti3C2Tx fibers can be fabricated from a colloidal 2D nematic phase dispersion. The layered conductive Ti3C2Tx fibers are ideal candidates for constructing high-speed ionic transport channels to enhance the electrochemical capacitive charge storage performance. In this work, we assemble Ti3C2Tx fibers with a high degree of flake orientation by a wet spinning process with controlled spinning speeds and morphology of the spinneret. In addition to the effects of cross-linking of magnesium ions between Ti3C2Tx flakes, the electronic conductivity and mechanical strength of the as-prepared fibers have been improved to 7200 S cm-1 and 118 MPa, respectively. The oriented Ti3C2Tx fibers present a volumetric capacitive charge storage capability of up to 1360 F cm-3 even in a Mg-ion based neutral electrolyte, with contributions from both nanofluidic ion transport and Mg-ion intercalation pseudocapacitance. The oriented 2D Ti3C2Tx driven nanofluidic channels with great electronic conductivity and mechanical strength endows the MXene fibers with attributes for serving as conductive ionic cables and active materials for fiber-type capacitive electrochemical energy storage, biosensors, and potentially biocompatible fibrillar tissues.

Mechanisms of the Planar Growth of Lithium Metal Enabled by the 2D Lattice Confinement from a Ti3C2Tx MXene Intermediate Layer

AbstractThe propensity of Li to form irregular and nonplanar electrodeposits has become a fundamental barrier for fabricating Li metal batteries. Here, a planar, dendrite‐free Li metal growth on 2D Ti3C2Tx MXene is reported. Ab initio calculations suggest that Li forms a hexagonal close‐packed (hcp) layer on the surface of Ti3C2Tx via ionic bonding and the lattice confinement. The ionic bonding weakens gradually after a few monolayers, resulting in a nanometers‐thin transition region of hcp‐Li. Above this transition region, the deposition is dominated by plating of body‐centered cubic (bcc) Li via metallic bonding. Formation of a dense and planar Li metal anode with preferential growth along the (110) facet is explained by the lattice matching between Ti3C2Tx and hcp‐Li and then with bcc‐Li, as well as preferred thermodynamic factors including the large dendrite formation energy and small migration barrier for Li. The prepared Li metal anode shows stable cycling in a wide current density range from 0.5 to 10.0 mA cm–2. The LiFePO4‖Li full cell fabricated with this Li metal anode exhibits only 9.5% capacity fading after 500 charge–discharge cycles at 1 C rate.

Three dimensional porous MXene/CNTs microspheres: Preparation, characterization and microwave absorbing properties

In this paper, a simple ultrasonic spray technology is used to assemble one-dimensional (1D) carboxylated carbon nanotubes (C-CNTs) and two-dimensional (2D) Ti3C2Tx MXene nanosheets into three-dimensional (3D) porous MXene/C-CNTs microspheres (MCM). After vacuum carbonization, C-MCM with excellent microwave absorbing properties are obtained. It finds that the synergy of MXene and CNTs makes C-MCM have good impedance matching and microwave attenuation capabilities. Under the best mass ratio (MXene: CNTs = 3:1) and filler content (30%), the minimum reflection loss (RLmin) is −45 dB@10 GHz, and the corresponding matching thickness is 2.7 mm. When the thickness is 1.9 mm, the effective absorption bandwidth (EAB) reaches 4.9 GHz. By adjusting the thickness of the absorber, almost all electromagnetic waves in the C, X and Ku bands can be completely absorbed. Therefore, C-MCM provides a new way to manufacture electromagnetic wave absorbers with light weight, thin thickness, high efficiency and broadband.

Addition of 2D Ti3C2Tx to Enhance Photocurrent in Diodes for High‐Efficiency Organic Solar Cells

Solution‐processed 2D Ti3C2Tx nanosheets are incorporated into the active layer of organic solar cells (OSCs) as a third component to obtain an enhancement of the photovoltaic device performance. The power conversion efficiency (PCE) of the devices is boosted from 9.34% to 10.72% for the PBDB‐T:ITIC blend and from 14.64% to 16.25% for the PM6:Y6 blend after adding 2D Ti3C2Tx nanosheets. The light scattering of the 2D flakes in Ti3C2Tx nanosheets not only increases the short‐circuit current density (JSC) but also improves the carrier dissociation and transfer efficiency in devices, thus leading to reduced bimolecular recombination. Furthermore, Ti3C2Tx with appropriate content has little effect on the interpenetrating network morphology and instead provides an additional pathway for charge transport in photoactive layers. Herein, a potential direction for the application of 2D Ti3C2Tx materials in the field of OSCs is provided.

High electrical conductivity and breakdown current density of individual monolayer Ti3C2Tx MXene flakes

High electrical conductivity and breakdown current density of individual monolayer Ti3C2Tx MXene flakes

Surface-tuned two-dimension MXene scaffold for highly reversible zinc metal anode

Zinc metal has aroused increasing interest as anode material of Zn-based batteries for their energy storage application. However, the uneven Zn stripping/plating processes induce severe dendrite growth, leading to low Coulombic efficiency and safety hazards. Herein, a surface-tuned two-dimensional (2D) MXene Ti3C2Tx scaffold as a robust skeleton is developed to facilitate the uniform Zn stripping/plating. The Ti3C2Tx with high electrical conductivity and unique structure provides fast ionic-transport paths, promising even Zn2+ stripping/plating processes. With suppressed Zn dendrite growth and uniform nucleation, the proposed 2D Ti3C2Tx scaffold for Zn metal anode delivers a low voltage hysteresis of 63 mV and long lifespan over 280 h. This surface-tuned engineering strategy demonstrates the potential application of Zn anode with MXene skeleton for next-generation Zn-based batteries.

Conductive and highly compressible MXene aerogels with ordered microstructures as high-capacity electrodes for Li-ion capacitors

Assembling two-dimensional (2D) materials into functional three-dimensional (3D) structures can enable their use in a wide variety of applications. For energy storage devices, 3D electrodes with high ionic and electronic transport properties and decent mechanical properties are expected to prompt the fabrication of the next generations of devices with high energy and power densities. Herein, we report a simple, efficient, and scalable process based on unidirectional freeze casting to fabricate ordered and porous 3D aerogels from 2D Ti3C2Tx MXene flakes. The fabricated aerogels show excellent mechanical, electrical, and electrochemical properties. Our studies show that the processing conditions significantly affect the properties of MXene aerogels. The electrical conductivity and mechanical properties of fabricated aerogels directly correlate with their structural features. The mechanical test results showed that MXene aerogels with ordered structures could withstand almost 50% of strain before recovering to their original shape and maintain their electrical conductivities during continuous compressive cycling. As electrode materials for lithium-ion capacitors, the fabricated aerogels delivered a significantly high specific capacity (~1210 mAh/g at 0.05 A/g), excellent rate capability (~200 mAh/g at 10 A/g), and outstanding cycling performance. We believe that the MXene aerogels with ordered structures have promising properties for a broad range of applications, including energy storage devices and strain sensors.