MXene is a new family of two-dimensional transition metal carbides or carbonitrides with graphene-like 2D morphology. The chemical formula of MXene is M_n+1X_nT_z, where M is an early transition metal, X is C and/or N, T stands for surface-terminating functional groups like F^-, OH^-, O^2-, etc., and n = 1, 2, or 3. It can be achieved by selective etching of the A element from the MAX phases, and HF is an etchant mostly used. First-principles calculations about MXene have been performed to reveal the structure and properties. MXene has also been found to have a unique two-dimensional layered structure, large specific surface area and good electrical conductivity, stability, magnetic and mechanical properties, and thus it is promising in many fields, including energy storage, catalysis and adsorption. This article reviews the quite recent progress of MXene based on theoretical and experimental considerations, especially its structure, synthesis, and applications. Finally, the suggestions about existing challenges and future developments are proposed. MXene is expected to be used for more various applications with further extensive research.

Cu/Ti₃C₂T_x composites with Ti₃C₂T_x content of 5vol%, 10vol% and 20vol% were prepared by using a molecular-level mixing process and spark plasma sintering (SPS). Influence of Ti₃C₂T_x content on electrical, mechanical and tribological properties was investigated. The result showed that relative density and electrical conductivity of Cu/Ti₃C₂T_x composites gradually decreased with the Ti₃C₂T_x content increase, while the tensile strength of Cu/Ti₃C₂T_x composites increased at first and then decreased. When the Ti₃C₂T_x content was 5vol%, the tensile strength of Cu/ Ti₃C₂T_x composites increased by 43% than that of pure copper. Tribological properties of Cu/ Ti₃C₂T_x composites were enhanced by the addition of Ti₃C₂T_x. When the Ti₃C₂T_x content was 10vol%, the wear rate of Cu/ Ti₃C₂T_x composites was 2.55×10^-7 mm³/(N·m), which was one magnitude lower than that of pure copper.

Two dimensional (2D) materials have attracted wide attention due to their ultrathin atomic structure, large specific surface area and quantum confinement effect which are remarkably different from their bulk counterparts. Anisotropic materials are unique among reported 2D materials. Their orientation-dependent physical and chemical properties make it possible to selectively improve the performance of materials. As representative examples, Re-based transition metal dichalcogenides (Re-TMDs) have tunable bandgaps in visible spectrum, extremely weak interlayer coupling, and anisotropic properties in optics and electronics, which make them attractive in the application areas of electronics and optoelectronics. In this riviev, the unique crystal structures and intrinsic properties of the Re-based TMDs semiconductors are introduced firstly, and then the synthetic method is introduced, followed by discussion on the unique physical characterizations and optimized means. Finally, prospects and suggestions are put forward for the preparation and research of ReX₂.

With the development of nuclear energy, the long-lived radionuclides are inevitably released into the natural environment during the mine process, fuel manufacture, nuclear power usable and spent fuel management, which are dangerous to human health and environmental pollution. Thereby the efficient elimination of radionuclides is an important parameter which affects the development of nuclear power. In recent years, the metal-organic frameworks (MOFs) have attracted worldwide attention in the adsorption of radionuclides from large volume of aqueous solutions, because of their high chemical stability, abundant functional groups and changeable porous structures. In this review, we mainly summarized the recent works of MOFs in the efficient removal of radionuclides, and to understand the interaction mechanism from batch adsorption experiments, model analysis, advanced spectroscopy analysis, and theoretical calculation. The adsorption capacities of MOFs with other materials were also summarized, and the future research opportunities and challenges are given in the perspective.

The technique for Materials Genetic Initiative (MGI) is the key tool for realizing the demand-oriented design of new materials assisted by the artificial intelligence (AI). Accordingly, the development and application of innovative intelligence algorithms are particularly important. Based on the generalization and analyses of the existing nature-inspired algorithms, this work aims at outlining the suggestion to build the nature-inspired algorithms library (NIAL). The potential route in which inspirations are obtained from varieties of disciplines, was used to produce new algorithms in high-throughput ways is introduced. The general procedure for building algorithm library is elaborated, while its advantages and characteristics are anatomized. Finally, the potential of NIAL in new materials development has been envisioned to enhance the standard for the application of AI including MGI.

All-inorganic cesium lead halide CsPbX₃ (X = Cl, Br, I) perovskite materials emerged as a rising star in the area of optoelectronics since 2015, due to its excellent photoelectric properties and environmental stability. Substantial progresses were made in the application of many electronic and optoelectronic devices, which attracted wide attention from the scientific community. This paper mainly reviews the latest research progress of cesium lead halide perovskite based planar heterojunction LED, where the structure and working principle of LED devices are briefly introduced. In addition, the classification and summarization of some optimization strategies for improving luminescence performance and working stability of LED devices are emphatically suggested, and the development trend of stable and efficient inorganic perovskite based planar heterojunction LED is finally prospected.

As the continuous development of the photovoltaic industry and the flat panel display devices, the demand for transparent electrodes is increasing rapidly. The most commonly used transparent conductive material, ITO, was criticized for its brittleness, which limited its application in the up-and-coming market. Cu nanowire transparent electrodes acts as promising candidate for the new generation of transparent electrodes due to their superior conductivity, low cost, easy accessibility and high flexibility. The synthesis of Cu nanowires and their application in transparent electrodes has drawn lots of attention. Progresses have been made in recent years. A comprehensive elaboration of the controllable synthesis of Cu nanowires through liquid synthesis methods and the mechanism behind them, the fabrication and post-treatment methods of Cu nanowire electrodes, the application of Cu nanowire electrodes in photovoltaic devices, transparent heaters and flexible devices are given. The trends of Cu nanowire electrodes is proposed.

Using Ti₃AlC₂ as the precursor, a new MAX phase Ti₃ZnC₂ was synthesized via an A-elemental substitution reaction in a molten salts bath. Composition and crystal structure of Ti₃ZnC₂ were confirmed by XRD, SEM and TEM analysis. Its structure stability and lattice parameter of Ti₃ZnC₂ were further proved by a theoretical calculation based on density function theory (DFT). Moreover, thermodynamics of A-elemental substitution reactions based on Fe, Co, Ni, and Cu were investigated. All results indicated that the similar substitution reactions are feasible to form series of MAX phases whose A sites are Fe, Co, Ni, and Cu elements. The substitution reaction was achieved by diffusion of Zn atoms into A-layers of Ti₃AlC₂, which requires Al-Zn eutectic formation at high temperatures. The molten salts provided a moderate environment for substitution reaction and accelerated reaction dynamics. The major advantage of this substitution reaction is that MAX phase keeps individual metal carbide layers intact, thus the formation of competitive phases, such as MA alloys, was avoided. The proposed A-elemental substitution reactions approach opens a new door to design and synthesize novel MAX phases which could not be synthesized by the traditional methods.

As a perovskite family member, SrTiO₃ shows significant applications in the fields of solar cells, photocatalysis, fuel cells and superconducting as a dependence of its crystallinity, morphology, crystal facet and optical properties. In this work, we reported an in-situ synthetic approach of SrTiO₃ nanostructures with modified morphology and tunable optical absorption properties based on conventional plasma electrolytic oxidation (PEO) associated with hydrothermal method. The morphology of SrTiO₃ nanostructures can be selectively modified from microcubes with smooth facets to ultrathin nanosheets by controlling the concentration of Sr source during PEO process. It is found that both SrTiO₃ microcubes and Sr_1-δTiO₃ nanosheets are well-crystallized single crystals. UV-Vis diffuse reactance spectrum (DRS) measurement reveals that Sr_1-δTiO₃ nanosheets with thin thickness show obvious blue-shift of absorption edge in comparison with SrTiO₃ microcubes due to the size effect. Finally, the morphology evolution and nucleation mechanism of SrTiO₃ nanostructures in-situ grown on PEO film is discussed.

All inorganic perovskite (CsPbX₃) nanocrystals has wide applications in the field of optoelectronic devices due to its excellent photoelectric characteristics, however, stability is still the bottleneck restricting its development. Combining with the current research progress, the BN/CsPbX₃ composite nanocrystals phosphors was synthesized via all-solid-state reactions. During the process, parameters of ball milling, ratio of reactants and other reaction conditions were optimized, thus the BN/CsPbX₃ composite nanocrystals can be stable in the air for more than 60 days. Its luminescence wavelength can cover the range of 417-680 nm with full width at half maximum of 23-47 nm, showing high color purity, and was further used in white LED with high stability and luminance. After placed in the atmosphere for a month, the attenuation of LED luminance is only about 0.7%, and less than 4% deterioration was observed after continuous work of 2 h, showing great working stability.

It’s essential to develop patterning deposition methods to simplify the process of device fabrication and then reduce the production cost. In this work, a new patterning deposition method, i.e. microfluidic method, was demonstrated in details. In this technology, a micro-fluidic channel with a width of 80 μm and a height of 2 μm can be constructed between PDMS modules and substrates, and under capillary force precursor drops will move through the channel to form a patterned liquid film which is then fixed on the substrate via thermal treatments, and finally patterned films are prepared. In addition, the thermal-driven solidification process from NiO_x precursor powder to oxide was investigated through thermogravimetric/differential thermal analysis (TG-DTA) measurement. And the evolution of phase structure of the NiO_x precursor powder was analyzed with respect to post-annealing temperatures. Finally, thin-film transistors were fabricated applying the patterned NiO_x thin films as channels, and the optimized device showed typical p-type transistor features, with a field-effect mobility up to 0.8 cm²·V^-1·s^-1.

Given the good electrochemical performance and excellent irradiation stability of two dimensional transition metal carbides (MXenes), the development of MXene-based electrode materials for radionuclide detection is very promising. In this work, Ti₃C₂T_x MXene was activated via an alkalization strategy to form K⁺ intercalated Ti₃C₂T_x (K-Ti₃C₂T_x). Then the modified electrode of K-Ti₃C₂T_x/GCE was prepared on glassy carbon electrode (GCE). Ti₃C₂T_x and K-Ti₃C₂T_x were characterized by XRD, SEM and XPS techniques, and the electrochemical detection performance of K-Ti₃C₂T_x/GCE for trace uranyl ion (UO₂²⁺) was further investigated. Cyclic voltammetry (CV) experiments showed that the electrochemical response of K-Ti₃C₂T_x/GCE modified electrode to UO₂²⁺ increased significantly. Under the differential pulse voltammetry (DPV) scanning at pH 4.0, the K-Ti₃C₂T_x/GCE modified electrode presented a good linear detection relationship for UO₂²⁺ in the uranium concentration range of 0.5-10mg/L. The detection limit of this method is 0.083 mg/L (S/N = 3), with decent stability and repeatability.

The stripping current arising from the oxidation of Cd was related to the concentration of Cd²⁺ in the sample. This study presents the determination of Cd(II) at low concentration μg/L levels by square wave anodic stripping voltammetry (SWASV) on an activated bismuth-film electrode (BFE). The electrode was initially modified by an electrochemical method, and then the electrodeposited bismuth-film was prepared again to improve the electrode, thereby enhancing the sensitivity to trace amounts of target Cd²⁺. The surface of glassy carbon electrode (GCE) before and after modification was characterizad by SEM, CV, EIS, and SWV. The parameters for the determination of the Cd²⁺ were investigated with the view of its application toward real samples containing low concentrations of Cd²⁺. Using the selected conditions, the limit of detection is 1 μg/L for Cd²⁺ at a preconcentration time of 10 min.

As a type of novel thin film solar cells, perovskite solar cells develope sharply within a decade, which efficiency has approached to that of the commercial silicon solar cells. However, its poor stability in the air has limited the further practical application. Herein, we achieve uniform sable perovskite films under open environment by adding some poly 4-vinylpyridine (PVP). The morphology, structure and performance test results show that the perovskite films added with PVP were more compact and uniform than the bare one. Moreover, the assembled solar cell with 0.4wt% PVP exhibited highly reproducible efficiencies up to 13.07%, much higher than that of 6.09% for the controlled one. When restored in the air with approximately 50% relative humidity in the absence of encapsulation, its efficiency decay time to a half from 3 d for bare one extended to 3 w. However, high PVP additives result in incomplete reaction between PbI₂ and CH₃NH₃I. If the above mentioned process is further optimized, is expected to be applied to the large-scale preparation of more stable perovskite film.

Fe, N doped 2D porous carbon catalyst was synthesized by pyrolysizing the precursor, ZIF-8, on graphene. Meanwhile, Fe-2,2-bipy were coordinated on ZIF-8. The catalyst was analyzed by SEM, XRD, and XPS for morphology, structure and component. The ORR and OER performance of the Fe, N doped 2D porous carbon catalyst were characterized by RDE, CV curves and LSV curves. It was found that the Fe, N doped 2 D porous carbon catalyst shows uniform 2D structure and that the content of Fe element is 1.32%. The catalyst shows 0.83 V half-wave potentials for oxygen reduction reaction (ORR) in 0.1 mol/L KOH solution and 420 mV over-potential for oxygen evolution reaction (OER) at 10 mA/cm² in 1 mol/L KOH solution. Then, a zinc-air battery was assembled using as-synthesized catalyst. The power density of zinc-air battery is up to 245 mV/cm². Furthermore, it shows superior cycling stability.

To achieve effective load of black TiO₂ nanoparticles and improve the practical application ability, the pulsed laser spraying was proposed. The composite coating was prepared on quartz glass substrate, which consisted of amorphous molecular sieve and rutile TiO₂ nanocrystals. The surface morphology of the composite coating was characterized, and a series of test about composite coating powder was conducted including absorption properties, phase structure, chemical valence, and photocatalytic properties. The results show that the coating is porous structure packed with 2-5 μm ball and has strong absorptive capacity in the visible region. In the process of pulsed laser sputtering, the molecular sieve changed to amorphous structure, and TiO₂ changed from anatase to rutile type. Ti⁴⁺ ion was reduced to Ti³⁺ ion, which resulted in reduced band-gap. The pulsed laser spraying technology achieves the fast load of the black nano TiO₂, which still has good photocatalytic ability under the full spectrum and visible light conditions.

Respiratory frequency and mode could be applied for medical diagnosis and health evaluation. Traditional medical diagnosing devices have bulky size and high cost, and are of inconvenience in use. To fulfill the urgent demand for high-performance, low-cost, and portable electronic devices, this study proposes to fabricate self-powered planar humidity sensors by inkjet-printing method by virtue of the characteristics that graphene oxide self-polarizes and is sensitive to humidity. This sensor linearly responds to the relative humidity, and both responds and recovers rapidly. In addition, this sensor possesses excellent sensitivity and stability after multiple cycling and long-term storage, and has realized monitoring of the respiratory frequency and mode. The humidity sensors in this work is ready to fabricate with low production cost, free from interference by body motion or exterior environment, and suitable for real-time monitoring respiratory frequency and mode.

To reveal influence of doping ions on the magnetic properties of strontium ferrite materials with magnetoplumbite configurations, we studied the stable configurations and magnetic structures of strontium ferrite with and without manganese doping. The results show that the strontium ferrite is ferrimagnetic, which is consistent with the previous reports. Comparing the GGA and GGA+U approaches, the U value exhibits a significant impact on the electronic structures and atomic magnetic moments. When 3.7 eV is adopted for U value, the system changed from a metal to a semiconductor with a spin up band gap of 1.71 eV. The total magnetic moment of the pure strontium ferrite is 40 μ_B. For the SrFe_12-xMn_xO₁₉ system, the site preference of Mn substituting Fe is investigated with x=0.5 and x=1.0. When x = 0.5, the single doping Mn atom preferentially occupies the Fe (12k) site. For x=1.0, the two Mn atoms preferentially occupy the Fe (12k) and Fe (2a) sites, respectively. Doping Mn has little impact on the lattice structure of strontium ferrite, but have a significant effect on the total magnetic moments and electronic structures. When x=0.5 and x=1.0, the band gap values for spin up electrons reduced to 0.85 and 0.49 eV, and the total magnetic moments reduced to 39 and 38 μ_B, respectively. This study may provide a theoretical foundation for future experimental studies.

Two-dimensional MXene nanosheets with vertical junction structure was employed for easy immobilization of horse radish peroxidase enzymes to fabricate the electrochemical hydrogen peroxide (H₂O₂) biosensor. The synthesized MXene nanosheets exhibited large specific area, excellent electronic conductivity and good dispersion in aqueous phase. Horse Radish Peroxidase (HRP) enzymes molecules immobilized on MXene/chitosan/GCE electrode demonstrated good electrocatalytic activity toward reduction of H₂O₂. The fabricated HRP@MXene/chitosan/GCE biosensor exhibited a wide linear range from 5 to 1650 μmol?L ^-1, a limit of detection of 0.74 μmol?L ^-1 and good operation stability. The fabricated biosensor was successfully employed for detection of trace level of H₂O₂ in both solid and liquid food.

In order to rapidly remove Eu(III) from aqueous solution, an alkalized two-dimensional titanium carbide, Na-Ti₃C₂T_x, was successfully prepared by treating inorganic two-dimensional transition metal carbide (MXene) with NaOH. Adsorption behavior of Eu(III) on Na-Ti₃C₂T_x was systematically investigated by batch experiments. The results show that the adsorption process is greatly affected by pH and ionic strength of the solution, and reached equilibrium within 5 min. Based on Langmuir model fitting results, the maximum adsorption capacity of Eu(III) on Na-Ti₃C₂T_x was calculated to be 54.05 mg/g at pH 4.0 under 298 K. The thermodynamic results suggested that the adsorption process was a spontaneous and endothermic reaction. The adsorption mechanism was further analyzed by energy dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (XRD) and extended X-ray absorption fine structure spectroscopy (EXAFS). These data revealed that Na ⁺ ions inside MXene galleries were exchanged by Eu ³⁺ ions and Eu(III) existed dominately in under outer-sphere surface complexation after adsorption under acidic pH conditions, but in inner-sphere surface complexation under near-neutral pH conditions. Due to its cost-effective prepatation and excellent sorption performance, Na-Ti₃C₂T_x may be a promising candidate for the efficient removal of trivalent minor actinides and lanthanides from radioactive wastewater.

In this work, Mo, Y, Al, and C were used as raw materials to synthesize a novel (Mo_2/3Y_1/3)₂AlC MAX phase by spark plasma sintering (SPS) at 1550 ℃, and the corresponding accordion-like MXene was successfully obtained with a milder chemical etching method. The chemical composition and microstructure of the materials were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and energy dispersive spectrometer (DES). The final product was Mo_1.33CT₂ MXene with functional groups on the surface. At the same time, the electronic structure and electronic properties of the novel (Mo_2/3Y_1/3)₂AlC MAX phase and the corresponding Mo_1.33CT₂ MXene were studied by the first-principles density functional theory. The calculated results show that all of them exhibit metallic properties, which are expected to be applied for energy storage, biosensors and electrocatalysis.

Recently, a new type of 2D transition metal carbides or nitrides (MXene) has attracted wide attention due to its large specific surface area, good hydrophilicity, metallic conductivity and other physical and chemical properties. 2D Ti₃C₂T_x MXene was obtained by etching Al layer of Ti₃AlC₂ with LiF and HCl and then mechanically delaminated. And the monolayer Ti₃C₂T_x nanosheets with lateral dimension of 625 and 2562 nm can be prepared by changing the intensity and way of mechanically delamination, as well as the centrifugation rate and time. Then their morphology, structure, composition, and electrochemical performance of Ti₃C₂T_x were studied. The results showed that the specific capacitance of Ti₃C₂T_x with smaller lateral size (<1 μm) can reach 561.9 F/g, higher than that of reported graphene, carbon tube and MnO₂ in the repotted literatures. And the Ti₃C₂T_x electrode still remained 96% of the initial specific capacitance after 10 ⁴ testing cycles.

As newly-discovered member of the MAB phases, Cr₄AlB₄ has much potential for high-temperature structural applications due to possible formation of a protective oxide scale. By use of “linear optimization procedure” and theoretical model of “bond stiffness” based on first-principle calculations, the phase stability and mechanical behavior of Cr₄AlB₄ were investigated. No imaginary frequencies in phonon dispersion indicate the intrinsic stability. The lower energy as compared with the set of other competing phases also shows the thermodynamic stability. Based on the quantificationally calculated bond stiffness by use of the model of “bond stiffness”, strong covalent bonding is present between Cr and B atoms as well as B and B atoms, while the Cr-Al (625 GPa) and B-Al (574 GPa) bond is relatively weak. It follows that Cr₄AlB₄ can be described as layered structure of strong covalently bonded Cr-B blocks interleaved by Al atomic planes where the bonding is relatively weak, similar to the well-known MAX phases, which demonstrates the similar damage tolerance and fracture toughness of Cr₄AlB₄ with the MAX phases.

Direct methanol fuel cells have good application prospects due to their advantages of convenient operation, high conversion efficiency, low operating temperature, low pollution, and easy storage and easy transportation of liquid fuel. However, existing anode catalysts have shortcomings such as low catalytic activity and poor resistance to CO toxicity which restrict its commercial application. In this study, a series of PtRu/(Ti₃C₂T_x)_0.5-(MWCNTs)_0.5 anode catalyst materials with different Pt and Ru ratios were prepared by three-step method. Ti₃C₂T_x was obtained by HF corrosion of Ti₃AlC₂, and acidified multi-walled carbon nanotubes (MWCNTs). After the compounding, Pt and Ru particles are supported by a solvothermal method. The synergistic relationship of Ru and Pt atoms was analyzed by XRD, SEM, EDS, TEM, and XPS. The results show that the Ru atoms are mixed with the Pt atoms to form PtRu bimetallic alloy with a particle size of about 3.6 nm. The electrochemical results show that the Pt₁Ru_0.5/(Ti₃C₂T_x)_0.5-(MWCNTs)_0.5 catalyst has the best electrochemical performance. Its electrochemical active area (ECSA) is 139.5 m ²/g, and positive peak current density is 36.4 mA/cm ².

Electromagnetic interference (EMI) shielding films with excellent mechanical properties are highly promising for applications in flexible devices, automotive electronics and aerospace. Inspired by the excellent mechanical properties of nacre derived from its micro/nanoscale structure, high-performance MXene/Cellulose nanocrystals (CNC) composite films were prepared by simple solution blending and followed vacuum-assisted filtration process. The presence of CNC significantly improves the mechanical properties with tensile strength increasing from 18 MPa to 57 MPa and toughness improving from 70 kJ/m ³ to 313 kJ/m ³. Meanwhile, the composite film still exhibits high electrical conductivity (up to 10 ⁴ S/m) and excellent EMI shielding efficiency (over 40 dB) with a small thickness of 8 μm.

Ge nanoparticles were synthesized uniformly on MXene sheets via a one-step chemical solution method. Morphology of Ge/MXene was characterized by SEM and TEM. Formation process and optimized synthesis condition was analyzed carefully. Ge/MXene was used as anode for lithium-ion batteries. Their electrochemical performances, including capacity, rate and cycling stability, were tested and evaluated. Ge/MXene exhibited a greatly improved capacity of 1200 mAh/g during the first hundred cycles at 0.2C with a loading of 1 mg/cm ². A capacity of 450 mAh/g at a higher loading of 2 mg/cm ² was obtained after 100 cycles. The excellence in electrochemistry is attributed to the high conductivity of MXene and its accommodable interlayer space.

Equal channel angular pressing (ECAP) followed by heat treatment was carried out to prepare Ag/Ti₃AlC₂ composites. Effects of heat treatment on the electrical resistivities and mechanical properties of the Ag/Ti₃AlC₂ composites were investigated. Results show that ECAP effectively densifies the Ag/Ti₃AlC₂ compacts, and layered Ti₃AlC₂ particles are delaminated and aligned due to shearing effect during ECAP. Alignment of Ti₃AlC₂ particles resulted in anisotropy of electrical and mechanical properties of the composites. Perpendicular to the alignment of Ti₃AlC₂ particles displayed high resistivity and compressive strength. Moreover, resistivity and compressive strength increased with following heat treatment, yielding the maximum at 800 ℃. These increments are attributed to the enhanced interfacial reactions between Ag and Ti₃AlC₂ at high temperatures. Findings in this study indicate that densification and microstructural control of Ag/MAX composites can be achieved simultaneously by ECAP, while the following heat treatment can tailor their properties.

Phase diagrams are used as an indicator to estimate the thermodynamic stabilities of the novel MAX phases (Ti₃AuC₂, Ti₃IrC₂, Ti₃ZnC₂, Ti₂ZnC). The phase diagrams of the Ti-Au-C, Ti-Ir-C, and Ti-Zn-C systems were obtained using the CALPHAD (Calculation of Phase Diagrams) approach coupled with ab initio calculations. The calculated results confirmed thermodynamic stabilities of the synthesized Ti₃AuC₂, Ti₃IrC₂, Ti₃ZnC₂, and Ti₂ZnC MAX phases, which is in great agreement with the experiment information. The present work shows a systematic method to calculate the thermodynamic stability of the novel MAX phases, which can be used as guidance to synthesize more undiscovered MAX phases.

Mn ²⁺ intercalation strategy to optimize the sodium storage performance of V₂C MXene was studied. The intercalated Mn ²⁺ not only enlarged the interlayer spacing of V₂C MXene but also formed a V-O-Mn covalent bond, which was beneficial to stabilize the structure of V₂C and inhibit the structural collapse caused by volume change during Na ⁺ decalation or intercalation. As a result, the intercalated V₂C MXene (V₂C@Mn) electrode showed a high specific capacity of 425 mAh·g ^-1 at the current density of 0.05 A·g ^-1, and 70% retention after 1200 cycles. This result clearly suggests that cations intercalated MXene has a great prospect in Na ⁺ storage.

Manganese-based oxides are promising cathode materials for zinc-ion batteries. However, these materials often suffer from rapid capacity fade due to structure collapse during charge and discharge processes. Here, we report that core-shell structured Mn₃O₄@ZnO nanosheet arrays are synthesized on the carbon cloth, combining microwave hydrothermal process with atomic layer deposition. With an optimized thickness of ZnO coating layer, the capacity retention of the as-formed Mn₃O₄@ZnO nanosheet arrays exhibits 60.3% over 100 discharge-charge cycles at a current density of 100 mA·g ^-1. It is demonstrated that the introduction of ZnO layers is beneficial to maintain the microstructure and improve the structural stability of the Mn₃O₄ electrode material during the discharge-charge process, benefiting from avoiding direct contact with the electrolyte. The design of the well-defined core-shell structure provides an effective way to develop high-performance manganese-based oxide cathode materials for zinc-ion batteries.

Cr₂AlC is a representative material in MAX phase family due to its combination of metallic and ceramic properties such as high electrical conductivity, high thermal conductivity, resistance to corrosion, good oxidation resistance. To further improve performance of Cr₂AlC, ZrC as a reinforcement was selected to reinforce Cr₂AlC matrix composites by hot pressing technique. Influence of ZrC content on the mechanical property of ZrC/Cr₂AlC composites has been investigated. The results showed that 10vol% ZrC/Cr₂AlC composite improved flexural strength (715 MPa) and Vickers hardness (7 GPa) by 80% and 106%, respectively, as compared with those of pure Cr₂AlC material. Date from this study indicate that Cr₂AlC MAX possesses broaden application potential.

With the development of wearable flexible electronic technology, the demand for flexible sensor with high sensitivity and wide sensing range is gradually increasing. The application of suitable conductive materials with high electrical conductivity and high flexibility as sensitive materials for sensors is the key to obtain high performance sensors. In recent years, MXene materials have become very promising sensitive materials due to their good conductivity, high flexibility, good hydrophilicity, and controllable synthesis. The types of MXene-based flexible force sensors, microstructure design of sensitive materials, sensing performance, and sensing mechanism analysis have been expound and summarized in this paper.

Phase diagrams, also known as equilibrium phase diagrams, serve as a road map for materials design. However, preparation process of coatings (such as Physical Vapor Deposition, PVD) is generally far from equilibrium and results in metastable phases. Thus, the CALPHAD (Calculation of Phase Diagrams) approach faces a challenge in calculating the metastable phase diagrams for PVD coating materials. Here we summarized the development of the modeling methodology for the metastable phase diagrams, where the model with critical surface diffusion distance established in recent years were highlighted. The CALPHAD approach, first-principles calculations coupled with high-throughput magnetron sputtering experiments were used to model the atomic surface diffusion, while only one key combinatorial experiment was performed to obtain the basic data for the computation, and the calculated metastable phase diagrams were confirmed by further experiments. Therefore, the database of the stable and metastable phase diagrams can be established, which will be used to guide the design of the ceramic coating materials by the relationship of composition, processing, microstructure, and performance. This model can also help to achieve the goal to shorten the time and reduce the costs of materials research and development.

MXenes—two-dimensional (2D) compounds generated from layered bulk materials, have attracted significant attention in energy storage fields. However, low mass loading of MXenes results in low areal capacity and impedes the practical use of MXenes electrodes. Inspired by natural basswood, an ideal architecture with natural, three-dimensionally (3D) aligned open microchannels was developed for high Ti₃C₂T_x mass loading. Compared with reported Ti₃C₂T_x electrode structure, the 3D porous carbon matrix has several advantages including low tortuosity, high conductivity and good structure stability. The Ti₃C₂T_x assembled with the wood carbon can deliver a high areal capacity of 1983 mF/cm ² at 2 mV/s with a high Ti₃C₂T_x mass loading of 17.9 mg/cm ² when used as electrode for supercapacitors. This work provides a new strategy to develop 3D porous electrodes for MXenes, which can achieve high areal capacity.

As a new two-dimensional transition metal carbides, MXene has various potential applications, such as energy storage, catalyst, composite material, and luminescent materials for their excellent physical and chemical properties. The element doping, geometrical defect, surficial functionalization, external electric field, and external strain can be used as effective methods for modulation of their properties. Ti₂CO₂, the thinnest Ti-based MXene, exhibits semiconducting character. The effects of electric field on the band structure of perfect primitive Ti₂CO₂ were explored in this work. The results revealed that the band gap of perfect primitive Ti₂CO₂ decreased with the increasing electric field. Carbon (C) vacancy in Ti₂CO₂ MXene was easily produced during the preparation process. Further investigation showed that the tensile strain could be used to regulate the conductivity of this system as the bands around the Fermi energy become smoother with increasing tensile strain. The investigation of charged C vacancy doped 2×2×1 Ti₂CO₂ indicated that its Fermi energy decreased with the increase of charge state. When it was +2 charged, the C vacancy doped 2×2×1 Ti₂CO₂ exhibited semiconducting character and owned a direct band gap of 0.489 eV.

Mo₂Ga₂C, a double-A-layer MAX, is reported to be films or powders. This paper researched the sintering properties of M₂Ga₂C powders to make dense bulk samples by vacuum hot pressing. It was found that 750 ℃ was a suitable sintering temperature, while higher temperature (850 ℃) resulted in decomposition of Mo₂Ga₂C yielding to main product of Mo₂C. During sintering process at 750 ℃, its grain size did not increase obviously with sintering time, meanwhile the size of pores decreased markedly and the relative density increased significantly with the increasing sintering time. Additionally, the hot-pressed samples had obvious texture. Due to layering, some grains changed their orientations during sintering, of which most of the (00l) planes in the hot-pressed samples preferred to be perpendicular to the direction of hot press. Almost fully densed Mo₂Ga₂C bulk (relative density: 98.8%) was obtained by hot pressing at 750 ℃ for 8 h. This advantage of the method suggested that it can serve as a promising preparation for Mo₂Ga₂C, a double-A-Layer MAX.

As a new class of two-dimensional transition metal carbon/nitride, MXenes have been proven to be a kind of pseudocapacitive supercapacitor electrode materials with excellent electrochemical property, and hold promise in practical use in the near future. In practical applications, it is required to make the electrode materials into planar porous electrodes for capacitor assembly. Herein, a simultaneous ammonization/carbonization method is proposed for the preparation of MXene planar porous electrode. Filter paper was used as a planar porous template, and MXene was coated on the fibers of the filter paper by means of dipping-drying, and then heat-treated in an ammonia atmosphere to obtain MXene/carbon planar porous composite electrodes. Analysis results show that the MXene nanosheets are uniformly coated on the carbonization-derived carbon fibers of the filter paper. When immersed 5 times, the areal capacitance reaches 403 mF/cm ² at a scan rate of 2 mV/s. After the composite electrode was tested for 2500 times in a galvanostatic charge-discharge cycle at a current density of 10 mA/cm ², the capacitance was almost the same as the initial capacitance, showing good rate performance and cycle stability. The MXene/carbon planar porous composite electrodes prepared by simultaneous ammonia/carbonization exhibit excellent electrochemical performance without using either polymer binder or metal current collector.

Ti₃C₂T_x@MnO₂ composites with different morphologies were prepared by liquid-phase coprecipitation and hydrothermal method using Ti₃C₂T_x@PDA as matrix, KMnO₄ as manganese source, CTAB or PEG as surfactant. Effect of MnO₂ morphology (δ-MnO₂ nanofragments, α-MnO₂ nanorods, α-MnO₂ nanoflowers and α-MnO₂ nanowires) on phase structure and electrochemical performance of Ti₃C₂T_x was analyzed by FE-SEM, XRD, Raman, FT-IR, BET, and electrochemical measurements. The results show that Ti₃C₂T_x@α-MnO₂ nanowires possesses better comprehensive electrochemical properties (340.9 F?g ^-1 at 2 mV?s ^-1), nearly 2.5 times higher than using CTAB, and smaller charge transfer resistance, as well as excellent cycle stability.

Ceramic matrix composites (CMCs) are promising candidates for application in aeroengine, aerospace aircraft thermal protection systems, nuclear power system, and other fields. At present, CMCs are developing from structural bearing materials to multi-functional composites. MAX phases are a group of layered ternary ceramics with excellent plastic deformation capacity, high electrical conductivity, good irradiation resistance and ablation resistance. Besides strengthening and toughening CMCs, the introducing MAX phases into CMCs can effectively improve the anti-irradiation, anti-ablation and electromagnetic interference shielding performance, meeting requirements of multi-functional CMCs. This paper reviewed the progress on MAX phases modified CMCs, design mechanism and application prospect.

In recent years, ternary layered carbide/nitride MAX phases and their derived two-dimensional nanolaminates MXenes have attracted extensive attention. The crystal structure of MAX phase is composed of M_n+1X_n unit interleaved with layers of A element. MAX phases combine good properties of metal and ceramic, which makes them promising candidates for high temperature structural materials, friction and wear devices, nuclear structural materials, etc. When etching the A-layer atoms of the MAX phase, the two-dimensional nanolaminates with the composition of M_n+1X_nT_x (T_x is surface termination), i.e. MXene, is obtained. MXenes have wide range of composition, and tunable physical and chemical properties, which endow them great potential in the applications of energy storage devices, electromagnetic shielding materials, and electronic devices, etc. In this paper, the research progress of MAX phase and MXene was introduced in terms of composition and structure, synthesis methods, and properties and application. Furthermore, the research prospects of this large family of materials were discussed.