MAX Phase Research Articles

Two-dimensional materials by large-scale computations and chemical exfoliation of layered solids.

MXenes are a family of two-dimensional (2D) materials typically formed by etching the A element from a parent MAX phase. Computational screening for other 3D precursors suitable for such exfoliation is challenging because of the intricate chemical processes involved. We present a theoretical approach for predicting 2D materials formed through chemical exfoliation under acidic conditions by identifying 3D materials amenable for selective etching. From a dataset of 66,643 3D materials, we identified 119 potentially exfoliable candidates, within several materials families. To corroborate the method, we chose a material distinctly different from MAX phases, in terms of structure and chemical composition, for experimental verification. We selectively etched Y from YRu2Si2, resulting in 2D Ru2SixOy. The high-throughput methodology suggests a vast chemical space of 2D materials from chemical exfoliation.

Ti3AlC2 MAX Phase: A surprising candidate material for highly selective and efficient gold recovery from strong acid solutions

Given the scarcity of natural gold sources and associated mining challenges, the recovery of gold from secondary sources, such as electronic equipment waste (e-waste), becomes imperative. E-waste is typically treated with aqua regia to obtain highly acidic gold-containing solutions, which are subsequently processed by various methods to recover gold. Gold recovery materials offer numerous benefits but often exhibit insufficient selectivity, efficiency, and cost-effectiveness. To address this problem, we herein used a nonmodified pristine Ti-Al-C MAX phase (Ti3AlC2) to realize the one-pot room-temperature recovery of gold from highly acidic solutions (pH < 1) in the form of easily collectable bulky ball-shaped Au0 aggregates. High gold selectivity (Kd = 2.03 × 106 mL/g) and extraction efficiency (∼99 %) were observed even in the presence of interfering metal ions (Pd2+, Pt4+, Co2+, Ni2+, Cu2+, Zn2+), and the maximum gold extraction capacity (>6000 mg/g) surpassed that of previously reported gold recovery materials. The recovered gold was highly pure (>90 mass%) and contained minimal amounts of the original MAX phase, which obviated the need for intensive postpurification. The results of instrumental analyses suggested that gold recovery relied on electron transfer, similar to cementation, and primarily involved the reduction of solution-phase Au3+ to Au0via electron transfer from the Ti and Al of Ti3AlC2. Thus, our work demonstrates the significant potential of pristine Ti3AlC2 for the energy-efficient recovery of gold from highly acidic solutions and paves the way for the efficient valorization of e-waste.

In Situ Growth of Interfacially Nanoengineered 2D-2D WS2/Ti3C2Tx MXene for the Enhanced Performance of Hydrogen Evolution Reactions.

In line with current research goals involving water splitting for hydrogen production, this work aims to develop a noble-metal-free electrocatalyst for a superior hydrogen evolution reaction (HER). A single-step interfacial activation of Ti3C2Tx MXene layers was employed by uniformly growing embedded WS2 two-dimensional (2D) nanopetal-like sheets through a facile solvothermal method. We exploited the interactions between WS2 nanopetals and Ti3C2Tx nanolayers to enhance HER performance. A much safer method was adopted to synthesize the base material, Ti3C2Tx MXene, by etching its MAX phase through mild in situ HF formation. Consequently, WS2 nanopetals were grown between the MXene layers and on edges in a one-step solvothermal method, resulting in a 2D-2D nanocomposite with enhanced interactions between WS2 and Ti3C2Tx MXene. The resulting 2D-2D nanocomposite was thoroughly characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman, Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses before being utilized as working electrodes for HER application. Among various loadings of WS2 into MXene, the 5% WS2-Ti3C2Tx MXene sample exhibited the best activity toward HER, with a low overpotential value of 66.0 mV at a current density of -10 mA cm-2 in a 1 M KOH electrolyte and a remarkable Tafel slope of 46.7 mV·dec-1. The intercalation of 2D WS2 nanopetals enhances active sites for hydrogen adsorption, promotes charge transfer, and helps attain an electrochemical stability of 50 h, boosting HER reduction potential. Furthermore, theoretical calculations confirmed that 2D-2D interactions between 1T/2H-WS2 and Ti3C2Tx MXene realign the active centers for HER, thereby reducing the overpotential barrier.

Binder-Free Two-Dimensional Few-Layer Titanium Carbide MXene Ink for High-Performance Symmetric Supercapacitor Device Applications

A heightened interest in developing MXene (Ti3C2Tx) for energy storage is evident in binder-free MXene ink being directly applied to current collector Ni-foam. Moreover, 2D titanium carbide MXene, with a few layers of nanostructure, has been prepared for symmetric supercapacitor device applications. As-prepared MXene nanosheets exist in two forms: dried powder and ink, achieved through wet-chemical etching and dimethyl sulfoxide delamination from the MAX (Ti3AlC2) phase. This comparative study of electrode devices involves (i) MX-dry powder with binder/additive electrodes and (ii) binder-free MXene inks with directly applied MX-conductive inks. The surface morphological images of pure MX-powder/ink display few layers, and material analysis reveals the good crystalline nature of delaminated MXene (Ti3C2Tx) inks. The electrochemical symmetric supercapacitor device performances of pure MXene powder and binder-free directly applied/coated MXene (Ti3C2Tx) ink, in terms of cyclic voltammetry (CV) and impedance spectroscopy (EIS), exhibit galvanostatic charge–discharge (GCD) curves that show high specific capacitance (Csp) at 105.75 F/g at a current density of 1 A/g. A comparison of active material electrodes demonstrated excellent cycle stability. Hence, in this work, we confirmed the superior capacitive behavior of binder-free MXene ink (MX-I) compared to conductive additives with polymeric binders included in MXene electrodes.

A novel formation mechanism: One-step synthesis of high-purity MAX phase bulk via enlarged reaction depth

The synthesis of high purity MAX phase bulk still faces a big challenge. In this study, we fabricated 98 vol% MAX phase bulk doped with Al2O3 nanoparticles through spark plasma sintering by using larger size TixAl1-x powders (particle size ∼100 μm) for the first time, in which 91 vol% Ti2AlN was the dominant component. The phase transition mechanism for Ti2AlN was deeply revealed by both experiments and theoretical calculations. Ti proportion of TixAl1-x powders played a key role in the formation of Ti2AlN, and increasing Ti proportion leaded to higher content of Ti2AlN. Both Al migration from TixAl1-x and TiN nanotwins generated by N vacancies could enlarge the reaction depth, resulting in fully transformation of larger size reactants and thus high purity MAX phase as obtained. Further, the transition model for the synthesis of Ti2AlN was accordingly proposed, which contained three stages and was additionally verified by experimental observations.

Effect of extrusion speed on properties of Cu−5vol.%Ti2SnC composite wire fabricated by friction stir back extrusion process

The effect of axial traverse speed of friction stir back extrusion (FSBE) process on the microstructure, mechanical, electrical, and wear properties of Cu−Ti2SnC composite wire was investigated. The FSBE process was performed on the primary composite made by the powder metallurgy method with 5 vol.% of Ti2SnC MAX phase. The results showed that as the extrusion speed increased, the twins formed in the microstructure increased, the Ti2SnC particles became finer, and the interface of bonding of the MAX phase−Cu matrix improved. The Cu−Ti2SnC composite wire fabricated at the rotational speed of 600 r/min and axial traverse speed of 25 mm/min showed the maximum hardness, yield strength, and ultimate tensile strength of HV 132.7, 278.34 MPa, and 485.15 MPa, respectively. This finding was due to its strong interfacial bonding and fine MAX phase particles. Besides, the larger grain size, the better interface bonding, and the lower the porosity resulted in the highest electrical conductivity of 89.21% (IACS) and least wear rate of 0.0015 mg/m of Cu−Ti2SnC composite wire fabricated at rotational speed of 600 r/min and axial traverse speed of 25 mm/min.

The elastic anisotropy, thermodynamic and tensile properties of Ti2AX (A = Al and Ga, X = C and N) MAX phases: first-principles calculations

The elastic anisotropy, thermodynamic and tensile properties of Ti2AX (A = Al and Ga, X = C and N) MAX phases: first-principles calculations

Topological signatures of Mo2TiC2O2

Mo2TiC2 is the Ordered Double Transitional Metal Layered Carbides (ODTMLC) derived from its parent MAX phases Mo2TiAlC2 by a wet chemical etching. Its oxidation was done by a new ablated plasma thrust method in which the MXenes were at 750 °C under an oxygen background in the pulsed laser deposition chamber. The reflective high electron energy diffraction technique assures the oxidation at the ambient gas pressure p = 0.1 mbar, which was described in the previous paper. The obtained Mo2TiC2O2 was transferred for their topological test under angle-resolved photoemission spectroscopy, circular dichroism test, and Chemical Potential (CP) analysis. An indirect energy bandgap of 125 meV was obtained. The sine function of α along with period π and β with period 2π shows that there is a possibility of helical spin textures in both α (electron-like pocket around Γ̄) and β (elliptical electron-like pocket around M̄). The CP analysis shows the possibility of at least 100 meV bandgap creation on a single surface so that the surface charges will flow without any effect of bulk. The Mo2TiC2O2 can be used as topological insulating material.

Probing the structural and electronic properties of MAX phases and their corresponding MXenes using first-principles calculations

Abstract This study delves into the theoretical exploration of the structural and electronic characteristics of 2D monolayer MXenes (M n + 1X n ) by the elimination of Al layers from their corresponding MAX-phases, M n + 1AX n (n = 1–3), through meticulous first-principles calculations. The study encompasses structural optimization and the determination of key ground state properties, including equilibrium lattice constants, energy (E 0), and volume (V 0) of both MXenes and their corresponding MAX phases. Consequently, we investigated the comparative study of the electronic properties of M n + 1AlC n (M = Ti, V, or Cr) (n = 1–3) and their MXenes for the first time by calculating the Bader charge analysis (MAX phase only) and the density of states (DOS). The analysis extends to the density of states and Bader charge assessments, facilitating a comprehensive comparison. Remarkably, the MXene monolayer showcases an elevated density of states at the Fermi level compared to its MAX phase counterpart. This disparity stems from the redistribution of 3d electrons near the Fermi level following the removal of Al layers, consequently enhancing electronic conductivity. Cohesive energy and formation energy calculations affirm the structural stability of these compounds. Furthermore, our computed values are meticulously cross-referenced with existing experimental and theoretical data, stimulating the reliability and significance of our findings.

Oxidation behavior of Ti2AlC MAX phase-based coating on a γ-TiAl alloy TiAl48-2-2 produced by DC magnetron sputtering

The application of intermetallic γ-TiAl-based alloys is limited by the deterioration in strength and creep resistance as well as reduction in oxidation resistance above 750 °C. The deposition of protective coatings is a promising opportunity to enhance the oxidation resistance or the lifetime with regard to the sustainability by several orders of magnitude. Moreover, additive manufacturing processes could enable the production of components with more complex geometries in the future. Thus, designs of γ-TiAl turbine blades with internal cooling systems could be feasible in the near future. In this context, the deposition of thermal barrier coatings and, therefore, oxidation protective bond coatings became important. MAX phases are of increasing interest as coating materials for high temperature applications due to their unique combination of metallic and ceramic properties. Especially the alumina forming MAX phases such as Cr2AlC, Ti2AlC or Ti2AlN are promising coating materials.In the present work a Ti2AlC MAX-phase based coating was deposited by DC magnetron sputtering. Using three pure elemental target materials - Ti, Al and C and a two-fold rotation, a homogenous all-around coating was applied on the γ-TiAl alloy TiAl48-2-2 with a coating thickness of 10 μm. After the deposition process the stochiometric Ti2AlC coating was X-ray amorphous, therefore a post-heat treatment at 800 °C for 1 h was performed to achieve the desired hexagonal phase. Finally, the MAX-phase coated TiAl48-2-2 alloy was subjected to a cyclic oxidation test at 850 °C in laboratory air. The Ti2AlC MAX-phase coated TiAl48-2-2 alloy exhibits an excellent oxidation behavior, due to the formation of a thermally grown alumina top layer with the desired hexagonal Ti2AlC MAX-phase below. Extensive TEM analyses also showed the dependence of Al2O3 formation on post-heat treatment. θ-Al2O3 with a lower protective effect and the concomitant formation of TiN under the TGO was observed with post-heat treatment in Ar, while post-heat treatment in air lead to the formation of a protective α-Al2O3 layer.

Optimization of Synthesis Conditions for Improving Ti3AlC2 MAX Phase Using Titanium Scraps

Optimization of Synthesis Conditions for Improving Ti3AlC2 MAX Phase Using Titanium Scraps

Impressive efficiency of zinc oxide-manganese oxide/MAX composite in two-electrode system for photovoltaic-electrolyzer water splitting

The improvement and use of affordable and efficient electrocatalysts for complete water splitting are crucial for the future of energy supply. Here, a hybrid zinc oxide (ZnO)–manganese oxide (Mn3O4)/Ti3AlC2 (MAX) composite produced by a facile hydrothermal synthesis is utilized as a dual-function electrocatalyst for the hydrogen and oxygen evolution reactions (HER and OER, respectively). Its well-organized surfaces and bulky porous framework provide numerous catalytically active sites during electrochemical reactions, leading to significant improvement in the HER and OER activities. In particular, the ZnO and Mn3O4 phases increase the catalytic activity of the electrode, while the MAX phase enhances the conductivity and promotes low overpotential Ni sites through charge transfer effects. Consequently, the optimized ZnO-Mn3O4/MAX/Ni foam electrode exhibits relatively low overpotentials (η) of 244 and 340 mV at 20 mA cm−2 for the HER and OER at 1.0 M KOH, respectively. The electrodes also demonstrate exceptional long-term stability during cycling for both the HER and OER. A fully homemade water splitter, using these electrodes as anode and cathode, achieves a current density of 10 mA cm−2 at a cell voltage of only 1.62 V. When integrated with commercially available silicon-based solar cells, combined PV-EC water splitting devices enable increased hydrogen generation from stimulated sunlight. This study presents a typical demonstrated and proven strategy for real large-scale solar hydrogen generation using cost-effective PV-EC technology.

Cr2AlC and metals reactivity: Sintering and oxidation

Cr2AlC-20 wt% (Sn; Cu; Co; Fe; Ag) powder mixtures were hot isostatically pressed at 1000 °C for 4 h under 150 MPa to investigate the possible alloying behaviour of the metals with the MAX phase. The as-synthesized bulk materials were further oxidized at 1000 and 1200 °C for 10 h under dry air flux to study the effect of the alloying on the oxidation performance of the MAX phase. The metallic elements did not dissolve into the MAX phase grains: they mainly acted as oxidizing agents on the MAX phase grains, draining the aluminum from it to form intermetallic phases. The oxidation tests resulted in the formation of an alumina scale for most of the samples. The oxidation kinetic study shows no improvement of the oxidation behaviour of the Cr2AlC-metal composites as compared to pure bulk Cr2AlC. Sn spheres embedded in an alumina layer and empty alumina shells are respectively observed on the surface of the oxidized Cr2AlC–Sn and Cr2AlC–Ag composites.

Stability and physical properties of two novel magnetic MAX phase compounds Fe2AB (A=Cu and Zn) from density functional theory

MAX phases exhibit a wide range of important physical properties, making them a significant area of research with various practical applications. In this paper, a theoretical study of two new magnetic MAX phases, Fe2CuB and Fe2ZnB, has been conducted using first-principles spin-polarized calculations. The focus is on exploring their structural, electronic, magnetic, elastic, mechanical, and thermodynamic properties in the hope of identifying attractive properties for potential technological applications. It has been found that Fe2CuB and Fe2ZnB are thermodynamically, dynamically, and mechanically stable. They are predicted to be ferromagnetic ductile and exhibit a degree of elastic anisotropy. Moreover, examination of the density of states (DOS) curves reveals the metallic and magnetic properties of the materials. Fe2CuB and Fe2ZnB exhibit total magnetic moment values of 7.77 μB and 6.47 μB, respectively. The significant difference in Curie temperatures between Fe2CuB and Fe2ZnB, with values of 1194 K and 310 K, highlights distinct thermal stability characteristics inherent in these MAX phases. We have discovered that Fe2ZnB is a promising candidate for high-temperature spintronic applications, while Fe2CuB may be suitable as a material for thermal barrier coatings (TBC) due to its low minimum thermal conductivity.

Optimization of passive Q‐switched fiber laser employing MAX phase chromium aluminum carbide film

AbstractIn this work, we proposed a mechanical exfoliation technique to compose a saturable absorber (SA) from MAX phase chromium aluminum carbide (Cr2AlC). The performance of a passive Q‐switched erbium‐doped fiber laser (EDFL) based on Cr2AlC‐SA was experimentally demonstrated. The optical properties of SA showed appropriate nonlinear absorption, with a non‐saturable absorption of 92.5%, and saturable absorption of 1.2%. The proposed EDFL was investigated using 50:50 and 80:20 output couplers (OCs). At 167 mW pumping power and 3 dB OC, the EDFL produced pulses with 2 μs width, and 163 kHz repetition rate. Moreover, with 80:20 OC, the EDFL produced shorter laser pulses with 1.46 μs width, and 135.2 kHz pulsing rate. The results reveal that the higher repetition rate with high energy can be obtained with a 3 dB coupler, while narrower pulse width is achieved with an 80:20 OC.

Generation of Q-switched and mode-locked pulses in erbium-doped fiber ring laser using saturable absorption of Ti2SnC

MAX phase materials have garnered significant attention due to their corrosion resistance, impressive antioxidation and high electrical and optical conductivity. One such material, Titanium Tin Carbide (Ti2SnC), has demonstrated notable nonlinear optical properties. The saturable absorption of Ti2SnC, embedded into a polyvinyl (PVA) film, was measured to assess its potential. The Ti2SnC -PVA film exhibited a calculated modulation depth of 7.8%. In the context of practical applications, the Ti2SnC-PVA film was employed as a saturable absorber (SA) in an Erbium-doped fiber laser (EDFL) cavity. This configuration enabled the generation of stable Q-switched and mode-locked pulse trains. Q-switched operation occurred in a pump power range of 51.67 mW–83.83 mW, reaching a peak pulse energy of 110.94 nJ. Transitioning to mode-locking operation, the laser cavity demonstrated efficiency in the pump power range of 105.27 mW–196.39 mW. At a pump power of 196.39 mW, the fiber laser cavity achieved its highest pulse energy of 5.42 nJ, characterized by a pulse width of 2.32 ps and a pulse repetition rate of 1.825 MHz. These results highlight the promising potential of Ti2SnC-PVA thin film as a cutting-edge material for applications in pulsed laser systems. The material's excellent nonlinear optical properties make it a compelling candidate for advancing the field of pulsed laser technology.

MAX Phase (Nb4AlC3) For Electrocatalysis Applications.

In search for novel materials to replace noble metal-based electrocatalysts in electrochemical energy conversion and storage devices, special attention is given to a distinct class of materials, MAX phase that combines advantages of ceramic and metallic properties. Herein, Nb4AlC3 MAX phase is prepared by a solid-state mixing reaction and characterized morphologically and structurally by transmission and scanning electron microscopy with energy-dispersive X-ray spectroscopy, nitrogen-sorption, X-ray diffraction analysis, X-ray photoelectron and Raman spectroscopy. Electrochemical performance of Nb4AlC3 in terms of capacitance as well as for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is evaluated in different electrolytes. The specific capacitance Cs of 66.4, 55.0, and 46.0 F g-1 at 5mV s-1 is determined for acidic, neutral and alkaline medium, respectively. Continuous cycling reveals high capacitance retention in three electrolyte media; moreover, increase of capacitance is observed in acidic and neutral media. The electrochemical impedance spectroscopyshowed a low charge transfer resistance of 64.76 Ω cm2 that resulted in better performance for HER in acidic medium (Tafel slope of 60mV dec-1). In alkaline media, the charge storage value in the double layer is 360 mF cm-2 (0.7V versus reversible hydrogen electrode) and the best ORR performance of the Nb4AlC3 is achieved in this medium (Tafel slope of 126mV dec-1).

Mechanical Properties of Ti3AlC2/Cu Composites Reinforced by MAX Phase Chemical Copper Plating.

Among the various reinforcement phases available in Cu-based composites, the unique layered structure and easy diffusion of A-layer atoms make MAX phases more suitable for reinforcing a copper matrix than others. In this study, Cu-coated Ti3AlC2 particles (Cu@Ti3AlC2) were prepared through electroless plating, and Cu@Ti3AlC2/Cu composites were fabricated via vacuum hot-press sintering. The phase composition and microstructure of both Cu@Ti3AlC2 powder and composites were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results demonstrate the creation of successful electroless copper plating to obtain a Cu coating on Ti3AlC2 particles. At 850 °C, a small amount of Ti3AlC2 particles decompose to form TiCx, while Al atoms from the A layer of MAX phase diffuse into the Cu matrix to form a solid solution with Cu(Al). The test results reveal that the density of the Cu@Ti3AlC2/Cu composite reaches 98.5%, with a maximum compressive strength of 705 MPa, which is 8.29% higher than that of the Ti3AlC2/Cu composite. Additionally, the compressive strain reaches 37.6%, representing an increase of 12.24% compared to that exhibited by the Ti3AlC2/Cu composite.

Corrosion resistance and conductivity behavior of Cr-Al-N MAX phase coatings prepared by magnetron sputtering technology

Chromium aluminum nitride (CrAlN) coatings containing Cr2AlN phase were prepared by unbalanced magnetron sputtering followed by annealing at 1000 °C. The crystal structures, X-ray diffraction patterns, and selected area electron diffraction patterns of the Cr2AlN phase were modeled using computer software and compared with experimental observations. A good agreement was found between the two sets of results, thereby confirming the presence of Cr2AlN phase in the coatings. While previous studies have demonstrated the formation of Cr2AlN phase theoretically, this study presents experimental evidence of its physical existence. The potentiodynamic polarization results and interfacial contact resistance measurements show that the CrAlN coating with Cr2AlN phase has excellent corrosion resistance (a corrosion current density of 5.35 × 10−7 A/cm2 and electrical conductivity of 5.5 mΩ·cm2) and is thus a promising candidate for the protection of fuel cell bipolar plates.

Flexible, transparent and conductive wearable electronic skin based on 2D titanium carbide (MXene) ink

Flexible and transparent conductors are essentially required in epidermal wearable devices such as electronic-skins (E-skins) that facilitate human interaction and biofeedback. However, due to the “trade-off” effect between high electrical conductivity and optical transparency, it is difficult to obtain transparent E-skins with high electrical conductivity. Furthermore, traditional transparent conductor is bulky and brittle which is not suitable for flexible and wearable applications. Herein, ultrathin two-dimensional (2D) titanium carbide (MXene) nanosheets with metallic conductivity, hydrophilic surface and excellent mechanical flexibility was proposed as a novel high-performance transparent conductor, which was further developed as wearable E-skins. Solution-processable MXene conductive ink was obtained by facilely etching Al from MAX phase for large-scale spray coating to obtain flexible transparent conductors. The flexible, transparent, and conductive MXene-based electrodes own a sheet resistance as low as 200 Ω/sq, while with high optical transparency of 60% @550 nm, which is sufficient for the applications of E-skins. Moreover, the transparent MXene-based soft E-skins also exhibits outstanding mechanical flexibility which could maintain its high opto-electrical performance even after 1000 cyclic bending tests. In addition, the robust flexible transparent MXene-based E-skins also could accurately identify the movements of human body including approaching, touching and pressing, which is essentially required in various application scenarios such as human-machine interactions, touch panels and healthcare sensors. The solution-processable flexible, transparent and conductive MXene-based E-skins holds tremendous potential in emerging wearable applications.