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The expansionary progression in electromagnetic (EM) technology brings convenience to production and life, but it also generates serious EM radiation, giving rise to information leakage and threatening human health. EM absorbers have attracted significant attention from researchers as an effective approach to mitigate EM radiation. Transition metal carbides give advantageous EM wave performance and reside at the frontier of absorbers due to their exceptional physical and chemical properties of high electrical conductivity, affluent functional tunability, stable chemical characteristics. This review focuses on the notable progress in the research on transition metal carbide-based composites, encompassing single Ti 3 C 2 T x MXenes, multi-component Ti 3 C 2 T x MXenes composites, and multi-component Mo 2 C composites, as well as exploring the auxiliary attenuation effect of structures. The shortcoming and challenge of these carbides, like lack of low-frequency absorption, scarce effective absorption bandwidth, and unelucidated attenuation mechanism are also raised. This review provides an overview of the current state of Ti 3 C 2 T x MXenes and Mo 2 C composites, offering valuable insights into the properties and potential applications of transition metal carbide-based composites. [Display omitted] • The EW wave absorption theory was briefly introduced. • The merits and fabrication strategy of transition metal carbide-based absorbers. • The absorption mechanism and performance of the absorbers of single, binary and multicomponent. • Prospects and shortcomings of transition metal carbide-based absorbers. [ABSTRACT FROM AUTHOR]

MXene composed of transition metal carbides, nitrides, or carbonitrate, is the most ornamented and rapidly expanding two-dimensional (2D) material. Due to its exceptional qualities, including its adjustable band gap, high thermal conductivity, charger mediator, superior electrical conductivity, and environmental adaptability, MXene is now attracting the interest of researchers. MXene possesses a strongly hydrophilic surface, ion exchange capabilities, and durable surface functional groups. This study provides an overview of the synthesis, properties, and prospective applications of MXenes in energy, sensing and environment sectors. Firstly, this article provides a brief overview of the MAX phase (including its characteristics and recent advancements) and MXene. Then, we thoroughly investigated the different etching techniques used in the synthesis of MXene. Moreover, various properties of MXenes, such as structural, optical, mechanical, magnetic, and electronic characteristics have been investigated. In addition, the potential applications of MXenes in various dynamic fields such as supercapacitor, energy storage and conversion, water splitting, electrochemical sensors and waste water treatment has been explored symmetrically. This study also focuses on the current progresses and future prospective relating to MXene, which will surely assist the scientists who are doing work in areas of academia and material sciences. [Display omitted] • MXenes offer structural tailoring for various elements during synthesis or post synthesis. • Overview of the dynamic properties of MXene in a nutshell. • MXene-based nanocomposites for energy conversion, supercapacitors, sensors and environment were highlighted. • Perspectives on the future opportunities and challenges of MXene were provided [ABSTRACT FROM AUTHOR]

High energy density lithium-sulfur batteries (LSBs) are regarded as a promising yet challenging advancement in battery technology. The frequent movement of polysulfide intermediates and sluggish solid-solid reaction kinetics commonly result in irreversible sulfur depletion, diminished coulombic efficiency, and restricted operational lifespan. The development of functional separators for LSBs is recognized as a highly effective approach to address these issues. The construction of functional separators has the potential to effectively mitigate the shuttle effect of polysulfides and promote the uniform deposition of lithium ions, thereby facilitating the formation of dendrite-free anodes. This paper provides a comprehensive overview of the modification techniques commonly employed for enhancing the performance of LSB. These techniques include the utilization of monatomic catalysts, transition metal oxides, transition metal carbides, transition metal sulfides, transition metal nitrides, transition metal borides, transition metal phosphides, transition metal selenides, heterostructures of transition metal compounds, as well as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs). Additionally, recent advancements in this field are integrated to address existing limitations and propose further enhancements. Furthermore, it integrates recent advancements in order to address the deficiencies and enhancements of functional diaphragms. The conclusion of the article emphasizes the superior commercial potential of the new flexible separator compared to the traditional polyolefin separator, indicating a promising direction for the future development of functional separators in order to enhance the performance of LSBs. [ABSTRACT FROM AUTHOR]

Cobalt carbide as a new type of transition metal carbides (TMACs) has received extensive attention in the field of magnetism and electrocatalysis. As one of the cobalt carbide materials, Co 2 C shows good hard magnetism. In this paper, we have designed a simple and efficient method to successfully prepare single-phase Co 2 C nanospheres. Co 2 C is synthesized by using Co 3 O 4 as precursor and small molecule amino ethylenediamine as carbon source. The material exhibits excellent hard magnetic properties, with saturation magnetization up (Ms) to 32.19 emu/g and coercivity up to 1111 Oe at room temperature. Co 2 C also demonstrats excellent hydrogen evolution reaction performance in 1 M KOH solution. Using nickel foam as the working electrode, the overpotential of only 92 mV can reach the current density of 10 mA cm−2, and the Tafel slope is 104 mV dec−1. This provides a new idea for the further development of synthetic cobalt carbide and its composite materials. • A new and simple method for synthesizing Co 2 C nanospheres was designed. • At room temperature, the saturation magnetization of the material can reach 32.19 emu/g and coercivity up to 1111 Oe. • Co 2 C can be used as catalyst for hydrogen evolution reaction. • In 1 M KOH solution, Co 2 C showed excellent HER activity (92 mV@10 mA cm -2 and 104 mV dec -1). [ABSTRACT FROM AUTHOR]

2D transition metal carbide/nitride (MXene) nanomaterials have prospective applications in high-performance microwave absorption (MA). However, the excessively high permittivity, absence of magnetic loss, and susceptible oxidizability of MXene severely hinder the enhancement of its MA properties. Here, we used a facile organic solution–phase thermal decomposition method to prepare dielectric–magnetic MXene@CoNi nanocomposites with heterojunctions, which can effectively prevent the oxidation of MXene. Subsequently, the MXene@CoNi nanocomposites were integrated with magnetic CoNi alloys, MXene microspheres (MXene MPs), and a silicon rubber (SR) matrix to construct multilayered CoNi/MXene@CoNi/MXene MPs/SR composites by casting and curing. Benefiting from the multilayered structure and complementary effects of the dielectric and magnetic components, the multilayered CoNi/MXene@CoNi/MXene MPs/SR composites composed of matching, absorbing, and reflective layers showed a remarkable minimum reflection loss of −53.3 dB and an ultra-broad effective absorption bandwidth up to 11.12 GHz at a thickness of 2.96 mm. These results demonstrated the developed multilayered composites are promising candidates for high-performance MA. Our study provides new insights into the development of ultra-broadband MXene-based absorbent materials. • The heterogeneous MXene@CoNi nanocomposites were prepared by organic solution-phase thermal decomposition method. • A structural design strategy for efficient MXene-based microwave-absorbing materials was proposed. • The appropriate impedance matching and enriched loss mechanism enhanced the microwave absorption properties. • The multilayered composites showed superior microwave absorption with RL min of −53.3 dB and EAB of 11.12 GHz. [ABSTRACT FROM AUTHOR]

The increasing energy crises and environmental pollution highlight the urgent requirement for exceptional functional materials. Two-dimensional (2D) transition metal carbides and/or nitrides (MXenes) are garnering growing interest and demonstrating competitive electrochemical applications in energy and environment due to their outstanding electrical conductivity, plentiful surface functional groups, excellent dispersibility, and high specific surface area. However, the aggregation and self-restacking of 2D MXene nanosheets are typically unavoidable throughout electrode fabrication, which will restrict the accessibility of their active sites and ion diffusion channels, and compromise their electrochemical properties. The creation of three-dimensional (3D) porous structures using 2D MXene nanosheets has been verified as a successful approach for enhancing surface utilization efficiency and reducing ion and mass transport distances, leading to the advancement of MXene and MXene-based composites with outstanding electrochemical performance. This review outlines some common approaches to construct 3D porous MXene architectures, including spray drying, template, assembly, gas foaming and 3D Printing methods. Meanwhile, the structure–property relationships of 3D porous MXenes and their electrochemical applications, such as supercapacitors, Li-ion battery, electrocatalysis, and electrosorption, are also pointed. Finally, the authors present a concise overview of on the potential, challenges, and future opportunities of 3D porous MXenes. [ABSTRACT FROM AUTHOR]

Perovskite solar cells have been a subject of great interest in photovoltaic research over the past decades due to their high efficiency and low cost. To improve the efficiency and stability performance, as well as lower the cost and complexity for fabrication of perovskite solar cells, careful device design, further material innovation and tailored interface engineering are still needed. Recently, there has been considerable interest in the newly discovered MXenes, a family of two-dimensional transition metal carbides, nitrides and carbonitrides, which have excellent metallic conductivity, abundant surface functional groups, solution processability, tunable work functions, high optical transparency and outstanding mechanical properties, making them promising materials for various applications. With tremendous success achieved, taking together with the strengths of MXene in perovskite solar cells has shown a broad outlook for future application. The explorations of MXene are of great significance for improving the performance and expanding the commercialization of perovskite solar cells, which are still in the early stages. Here, this comprehensive review focuses on the various merits of MXene: as additive in the function layers, as electron transport layers or hole transport layers, as the interface layers, as the electrodes and as multi-roles in sequence, in enhancing the performance and facilitating the application of perovskite solar cells, with the relevant mechanisms behind explained. In detail, the basic properties and production of MXene, and structures of perovskite solar cells are also summarized. With this knowledge, we suggest a broad perspective for designing, preparing, and passivating perovskite solar cells for future innovations by utilizing MXene with high performance. [ABSTRACT FROM AUTHOR]

To accelerate the transition to a green economy based on hydrogen, more efficient and cost-effective electrocatalysts should be adapted. Among them, transition metal carbides, particularly Mo 2 C, have gained significant attention within the scientific community due to their abundance and potential for high performance in the hydrogen evolution reaction (HER). This study introduces a bottom-up approach involving chemical vapor deposition, impregnation in solvent containing the Mo precursor and thermal annealing processes to carburize the Mo nanostructures anchored on vertical graphene nanowalls supports (GNWs). The role of GNWs is highlighted in the above processes. First, they provide abundant defective sites on their edges, which facilitate the binding of the metal compound molecules. Second, they provide C species during the annealing process which migrate and react with the transition metal to carburize it. Thus, they act as both C precursor and support system. Electrochemical characterization shows that the hybrids can be very efficient electrocatalysts towards hydrogen evolution reaction in acid electrolyte. When used as a cathode in a cell, it requires only − 141 mV to generate 10 mA/cm2 and shows excellent stability after hours of operation, making them highly promising for practical applications. This study paves the way for the design of hybrid nanostructures, utilizing nanocatalyst deposition on three-dimensional graphene supports. Such advancements hold great potential for driving the development of sustainable and efficient hydrogen production systems. [Display omitted] • Description of a facile route for deposition of Mo2C on vertical graphene nanowalls via drop-casting of MoCl5 precursor. • Identification of GNWs role as support system and carbon precursor during Mo carburization during annealing. • Excellent properties of hybrid compound as electrocatalyst towards hydrogen evolution. • Electrochemical Durability and structural stability in harsh acidic conditions. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) transition metal carbide MXene (Ti 3 C 2 T x) exhibits great potential in electromagnetic wave (EMW) absorbing materials due to its abundant surface functional groups and defects, tunable conductivity and high specific surface area. The Co@NC/TiO 2 /C composites were successfully synthesized through a solvothermal method and carbonization process using Ti 3 C 2 T x /Co-BTC as precursor. The incorporation of magnetic metal Co nanoparticles and Rutile-TiO 2 effectively addresses the issue of single loss mechanism in Ti 3 C 2 T x. The results show that CTC-100 exhibits excellent EMW absorption performance with a minimum reflection loss (RL) value of −51.3 dB at a thickness of only 1.48 mm, and the corresponding effective absorption bandwidth is (EAB, RL < −10 dB) 4.3 GHz. Simultaneously, by adjusting the matching thickness of the material from 1.29 mm to 5.0 mm, the EAB can achieve 15.42 GHz (from 2.85 GHz to 18 GHz). The excellent EMW absorption performance of CTC-100 composite is primarily attributed to the synergistic effect of magnetic loss and dielectric loss. This study provided an effective strategy for the design of Ti 3 C 2 T x -based EMW absorbing materials with high absorption intensity, reduced thickness, and broad effective absorption bandwidth (EAB). [Display omitted] • N-doped carbon-coated Co metal is successfully anchored on the conductive carbon layer to form Co@NC/TiO 2 /C. • The synergistic effect of magnetic loss and dielectric loss optimize the impedance matching. • The RL min value of CTC-100 is −51.3 dB at 14.17 GHz, with a thickness of only 1.48 mm. • The loss mechanism diagram illustrates the loss process of Co@NC/TiO 2 /C to electromagnetic waves. [ABSTRACT FROM AUTHOR]

Flexible lithium-ion batteries (LIBs) have gained significant interest as potential power source solutions for wearable and flexible electronic devices. However, the fabrication of flexible LIBs with optimal flexibility, mechanical stability, and high energy density remains a formidable challenge for researchers. Transition metal carbides are being investigated as capable anode materials for advanced lithium-ion batteries. In this study, we explore the growth of molybdenum carbides (Mo 2 C) and vertically-oriented graphene nanowalls (VGNWs) on flexible graphite paper (Papyex®) and their potential application as anode material for Lithium-Ion batteries (LIBs). Our approach involves a bottom-up synthesis of binder-free hybrid electrodes through the deposition of Mo carbide nanostructures on VGNWs using a combination of chemical vapour deposition, magnetron sputtering, and thermal annealing processes. The hybrid structure of Mo 2 C/VGNWs exhibits distinct and specialized attributes, including remarkable structural durability, small particle size, and a porous configuration. These features effectively promote the accessibility of electrons and ions to the interface between the electrode and electrolyte. Our electrochemical tests demonstrate that the Mo 2 C/VGNWs hybrids show superior lithium storage behavior when compared to VGNWs/Papyex® electrodes. The synergistic effects of the Mo 2 C nanoparticles and the highly conductive VGNW are mainly responsible for the enhanced electrochemical characteristics. [Display omitted] • Vertically-oriented graphene nanowalls (VGNWs) templates grown on Papyex® flexible paper. • The deposition of nanostructured Mo on VGNWs via magnetron sputtering. • In-situ Mo carburization through thermal annealing in Ar atm. • The size of Mo 2 C particles depends on the thermal annealing duration. • Importance of VGNWs functionalization with Mo 2 C particles for a 5-fold increase in the electrochemical performance, when compared to bare VGNWs [ABSTRACT FROM AUTHOR]

With the continuous development of microwave technology, the electromagnetic (EM) environment we face is becoming increasingly complex. EM wave absorbing materials, which convert EM wave energy into other forms of energy such as thermal energy, have attracted much attention in EM shielding technology for reducing and isolating EM interference. Finding absorbing materials with both strong and wideband absorption performance in 2–18 GHz is particularly important. In this paper, (Zr 0.2 Ti 0.2 Hf 0.2 Ta 0.2 Cr 0.2)C, (Zr 0.2 Ti 0.2 Hf 0.2 Ta 0.2 Ni 0.2)C, (Zr 0.2 Ti 0.2 Hf 0.2 Nb 0.2 Cr 0.2)C and (Zr 0.2 Ti 0.2 Hf 0.2 Nb 0.2 Ni 0.2)C high-entropy carbide powders were prepared through calculation and design, and their properties were compared with TaC and NbC. According to the analysis of phase composition, microstructure, and EM wave absorption performance, the prepared high-entropy carbides have formed single-phase solid solutions, and their absorption performance has been improved. It can be noted that (Zr 0.2 Ti 0.2 Hf 0.2 Nb 0.2 Ni 0.2)C has the minimum reflection loss (RL) of − 42.61 dB, and it has the maximum effective absorption bandwidth (E AB) of 3.60 GHz at the thickness of 1.00 mm. Through the analysis of EM parameters, it was found that high-entropy carbides with different compositions changed the dielectric loss, magnetic loss, and their coupling effect. This provides important insights for designing absorbing materials with ultra-thin and good conductivity. [Display omitted] • High-entropy carbide powders containing magnetic elements were successfully prepared. • The electromagnetic wave absorption performance of high-entropy carbides is improved compared to that of metal carbides. • (Zr 0.2 Ti 0.2 Hf 0.2 Nb 0.2 Ni 0.2)C exhibits excellent EM wave absorption performance, with the minimum reflection loss of − 42.61 dB at 5.25 mm, and the maximum effective absorption bandwidth of 3.6 GHz at the ultra-thin thickness of 1.00 mm. [ABSTRACT FROM AUTHOR]

Abstract Transition metal carbides serving as anode materials for lithium-ion batteries attract increasing attention owing to their high capacity and excellent conductivity. In this article, pomegranate-like granules assembled by carbon coated molybdenum carbide nanocrystallites (MoC@C) are fabricated through facile carburization of metal-organic framework precursor of trimesic acid Molybdenum (Mo 3 (BTC) 2). The pomegranate-like structure not only offers short diffusion paths for Li+, but also relieves the volume variations during the Li+ insertion/extraction process. The size of MoC nanocrystallites and the content of carbon coating can be optimized by adjusting the carburization temperature. The optimal MoC@C-700 sample exhibits superior cycle stability and high-rate performance. At 200 mA g−1, it shows reversible capacity of 647.3 mAh g−1. Even when the current density increases to 1 A g−1, it still delivers 570.6 mAh g−1 in the first cycle and maintains 509.8 mAh g−1 after 500 cycles. The high capacity and stable cycling performance indicate the pomegranate-like MoC@C composites may be promising for high-performance lithium-ion batteries anode. Graphical abstract Image 1 Highlights • Pomegranate-like MoC@C has been fabricated through carburization of MOF precursor. • The carbon coating confines the growth and agglomeration of MoC nanocrystallites. • The MoC@C composite exhibits superior cycle stability and rate capability. [ABSTRACT FROM AUTHOR]

Benefiting from rich surface functional groups, two-dimensional transition metal carbides (MXene) exhibit excellent metallic conductivity, hydrophilicity and film-forming properties and are widely used in energy storage and microwave absorption. However, the agglomerate and stacking of MXene nanosheets during preparation are largely detrimental to the full realization of their merits at two-dimensional scale. Therefore, we developed an ultrasonic assisted and vacuum filtration method to obtain MXene/CuS thin film electrode material with a "sandwich" structure without destroying its inherent properties, which still maintains a good lamellar structure and exhibits excellent tensile properties. Due to the synergistic effect of MXene and CuS and their redox reaction, the MXene/CuS thin film electrode exhibits a specific capacitance of 491 F g−1 at a current density of 1 A g−1. It can be used directly as positive and negative electrodes to assemble a flexible supercapacitor with a capacitance retention of 89 % at current density of 2 A g−1 after 5000 cycles. In addition, the composite can achieve an effective absorption band width of 3.3 GHz (14.7–18 GHZ) at a thickness of 1 mm. The study shows that layer spacing modulation offers the possibility of large-scale applications of MXene in the field of flexible supercapacitors and microwave absorption, and provides new ideas for the development of multi-purpose materials to meet the needs of different applications. [Display omitted] • MXene/CuS nanofilms with a laminar morphology are obtained by a gentle method. • The obtained MXene/CuS thin film electrode has excellent flexibility. • Combined characterization reveals energy storage and EMW absorption mechanism. • The capacity retention rate of the device reaches 89% after 5000 cycles at 2 A g−1. • Effective absorption broadband is up to 3.3 GHz (14.7–18 GHz) at 1 mm thickness. [ABSTRACT FROM AUTHOR]

Zinc air batteries (ZABs) are considered as one of the most promising energy storage and conversion devices due to their high theoretical energy density and low cost. They generate and store energy through electrochemical reactions, such as oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). But, the sluggish kinetics of ORR and OER prevents them from achieving the maximum efficiency. Although, noble metal (Pt, Pd, Ir) based catalysts are considered as benchmark catalysts for ORR and OER, their high cost and poor stability during the reactions restrict their large-scale commercialization. Recently, transition metal carbides (TMCs) and nitrides (TMNs) were investigated for ZAB applications due to the higher catalytic activity, lower costs and better stability. Hence, this review mainly based on the discussion of various TMCs and TMNs, and focused on the application for ZAB and the problems associated with the development of TMCs and TMNs based catalysts. Further exploration was conducted on how to overcome these issues with feasible technical methods, such as heteroatom doping, compositing with carbonaceous materials etc. [Display omitted] • TMCs and TMNs based electrocatalysts for zinc air-batteries were reviewed. • Noble metal like properties of TMCs and TMNs enhance their bifunctional activity. • Recent advances in design, synthesis and performance of TMCs and TMNs were discussed. • The research trend towards the TMCs and TMNs have been highlighted. [ABSTRACT FROM AUTHOR]

With the development of electronic products to miniaturization and high frequency, high-performance flexible electromagnetic interference (EMI) shielding materials are urgently needed to deal with electromagnetic pollution. Two-dimensional transition metal carbide/polyimide (Ti 3 C 2 T x MXene/PI) films were synthesized by in situ polymerization and a simple scratch method in this paper. The Ti 3 C 2 T x MXene nanosheets give the films good EMI shielding effectiveness (SE) and electrical conductivity. Specifically, the film with a thickness of 0.11 mm (Ti 3 C 2 T x content of 30 wt%) exhibits an EMI SE of 34.73 dB and a specific EMI SE (SE/thickness) of 315.73 dB/mm in the frequency range of 8.2–12.4 GHz (X-band). In addition, the films have a tensile strength of 67.58 MPa, and a high decomposition temperature of 510 ℃ in N 2 atmosphere. Therefore, we believe that the prepared Ti 3 C 2 T x /PI films with good comprehensive performance have enormous potential in the field of lightweight and flexible EMI shielding materials. • Ti 3 C 2 T x MXene/Polyimide composites film was synthesized by in situ polymerization and scraping method. • With the increase of Ti 3 C 2 T x MXene content, the electrical conductivity and EMI SE of the films increased. • The films exhibit good flexibility and tensile properties. • The film with thickness of 0.11 mm exhibited 34.73 dB EMI SE when Ti 3 C 2 T x MXene was added at 30 wt%. [ABSTRACT FROM AUTHOR]

The IVB transition metal carbides, MC, (M = Ti, Zr and Hf, respectively) and the synthesis of M 3 (Si/Al)C 2 have been extensively studied due to their excellent mechanical, thermal and electrical properties. In this work, the effects of solute atoms (Si/Al) on the deformation mechanism and ideal strengths in various MC (M = Ti, Zr, Hf) systems are investigated systematically using first principle calculations. The deformation mechanisms of MC may vary from the glide of perfect dislocation to twinning once Si/Al solute atom concentration ( η ) in the glide plane reaches some critical value, indicating that the stacking faults and twin structures may appear in the region with high solute concentration, such as grain boundary, which agrees with the experimental results. Compared with MC, the ideal tensile/shear strengths of M 3 (Si/Al)C 2 decreases obviously, which can be attributed to weak M–(Si/Al) bonds in contrast to M–C bonds. [ABSTRACT FROM AUTHOR]

Ti 3 C 2 T x is promising negative electrode materials for asymmetric supercapacitor (ASC). The Ti 3 C 2 T x sheets are obtained by etching Ti 3 AlC 2 powders in the mixture solution of HCl and LiF, then vacuum filtrated to achieve a free-standing Ti 3 C 2 T x -paper. The electrochemical performance of Ti 3 C 2 T x -paper was measured and a high volumetric capacitance of 295.4 F cm −3 was achieved. Meanwhile, it exhibited a high capability rate of 79.7% from 2 mV s −1 to 100 mV s −1 and long cycle life with 94.4% retention of its initial after charged and discharged for 15000 cycles at a current density of 10 A g −1 . ASC devices were fabricated using Ti 3 C 2 T x -paper as negative electrode and carbonized filter paper as positive electrode. The energy density and power density of ASC device are 4.5 Wh kg −1 and 1.3 kW kg −1 , respectively. The application of the device has been demonstrated by lighting red light emitting diode, endowing prospect of the Ti 3 C 2 T x -paper as negative electrode for supercapacitors. [ABSTRACT FROM AUTHOR]

The development of high-performance electromagnetic interference (EMI) shielding materials is urgently needed to mitigate electromagnetic radiation pollution. Two-dimensional transition metal carbides (MXenes) are promising EMI shielding materials because of their high metallic electrical conductivity. However, tuning the EMI shielding performance of MXene composites remains challenging via the structure engineering strategy. Herein, we develop a layer-by-layer assembling strategy to construct multilayer sandwiched hollow magnetic Fe 3 O 4 nanospheres (HFO)/MXene on flexible nonwoven fabrics. The fabricated Fe 3 O 4 /MXene composite fabrics (HFMs) exhibit low sheet resistance (4.6 Ω/□), super-hydrophobicity, self-cleaning, and good EMI shielding performance (EMI shielding effectiveness of 33.28 dB). More importantly, the EMI shielding mechanism of HFMs is tunable according to the loaded active materials. Thus, the mechanism can alternate from absorption to reflection. Moreover, the HFMs exhibit good electrothermal performance and can be used as a wearable heater for personal thermal management. This work provides a new approach for the structural design of high EMI shielding materials, and paves the way for the development of wearable electronics. • hollow Fe3O4 nanospheres (HFO) are synthesized via the hydrothermal method. • Multilayer sandwiched HFO/MXene modified fabrics (HFMs) are fabricated. • HFMs have high EMI shielding efficiency of 33.28 dB. • HFMs exhibit tunable EMI shieling mechanism. • HFMs show good super-hydrophobicity and electrothermal performance. [ABSTRACT FROM AUTHOR]

Molybdenum carbide (Mo 2 C) was regarded as one of the most promising catalysts for hydrogen evolution reaction (HER) due to its Pt-like electronic structure. In practice, however, the catalytic performance of Mo 2 C is always hampered by the inevitable oxidation on its surface. Herein, we developed a simple and efficient strategy to improve the HER activity of Mo 2 C using sulfur as a "modifier", in which sulfur atoms were used to replace a portion of the oxygen atoms in the surface oxide layer to activate the surface. The experimental results demonstrated that a moderate sulfur modification could significantly improve the HER performance. Theoretical studies further revealed that the strong hydrogen bonding of Mo atoms in the oxide layer is the primary reason that impairs HER performance, whereas the S modification can shift down the d -band center of Mo, effectively weakening the Mo-H bond. As expected, the S-modified Mo 2 C exhibited superior performance, affording a low overpotential of 117 mV at 10 mA cm−2 for catalyzing the HER in 0.5 M H 2 SO 4. This work provides a convenient and effective way for the development of transition metal carbide catalysts. [Display omitted] • A surficial activation strategy was proposed to improve the HER performance of Mo 2 C. • Sulfur was employed as a "modifier" to achieve surface activation. • A moderate surficial sulfur modification could effectively improve HER performance of Mo 2 C. • DFT calculation revealed that the key to surface activation is the weakening of the surface Mo-H bond. [ABSTRACT FROM AUTHOR]

The self-healing performance of anticorrosive coatings is critical to restoring their protective function in the event of failure to ensure durability in harsh corrosive conditions. In this work, a novel self-healing anticorrosive coating was fabricated by two-dimensional transition metal carbides and carbonitrides (MXenes) and mesoporous silica nanoparticles (MSNs) loading tannic acid (TA) as corrosion inhibitors that can effectively protect low-carbon steel from corrosion damage. The TA as corrosion inhibitors were loaded into the mesoporous silica nanoparticles, and the loading capacity reached about 71.71%. The synthesized epoxy/TA@MXene-SiO 2 coating was characterized in detail using different tools. The epoxy/TA@MXene-SiO 2 coating had excellent anticorrosive performance and an impedance modulus of 2.826 × 106 Ω cm2 at 0.01 Hz. The impedance modulus reached the maximum peak value of 8.585 × 106 Ω cm2 after 132 h of continuous immersion. In addition, the TA made a coating with an electrochemical self-healing efficiency of 114.27 kΩ cm2 h−1. This work provides insight into the novel design of anticorrosive coatings with excellent anticorrosive performance and high self-healing efficiency. • The loading capacity of TA as corrosion inhibitors in TA@MXene-SiO 2 reached about 71.71%. • The epoxy/TA@MXene-SiO 2 coating had excellent anticorrosive performance and impedance modulus of 2.826 × 106 Ω cm2 at 0.01 Hz. • The impedance modulus reached the maximum peak value of 8.585 × 106 Ω cm2 after 132 h of continuous immersion. • The TA made coating with an electrochemical self-healing efficiency of 114.27 kΩ cm2 h−1. [ABSTRACT FROM AUTHOR]

Human thermal comfort management, motion capture and protection are highly needed in electronic wearable devices for their stretchability, wearing comfort, and versatility. Multifunctional smart textile becomes a favorable solution. Here, multifunctional electronic knitted fabric for strain sensing and thermal management is provided by a simple dip-coating process, involving the deposition of one-dimensional (1D) silver nanowires (AgNWs) and two-dimensional (2D) transition metal carbide/carbonitride (MXene) nanosheet. This multifunctional knitted fabric possesses excellent mechanical durability (>1000 cyclic stretching) and a wide strain sensing range limitation (~445%) comes from the high elastic knitted fabric. In addition, outstanding Joule heating (When the current is 0.10 A (A), the fabric can reach an equilibrium temperature of around 126 °C within 37 s, with a great electrothermal conversion efficiency h r+c of 0.13 and a maximum heating rate of 9.73 °C/s) and temperature sensing performance (temperature coefficient of resistance (TCR) of − 0.07%/°C) are achieved. Moreover, this smart fabric gives a high EMI shielding performance (44 dB). This work provides multifunctional AgNWs/MXene fabric using a simple dip-coating process for physical monitoring, wearable thermal management and other applications. • A high stretchable AgNWs/MXenes conductive network derived from knitted fabric was provided. • This AgNWs/MXenes fabric is capable of high electrothermal conversion efficiency (h r+c of 0.13), large strain (~445%) and temperature sensing, and EMI shielding. [ABSTRACT FROM AUTHOR]

The main factor affecting the electrochemical performance of Li-ion hybrid capacitor (LIHCs) is the imbalance of kinetics between anode and cathode. Although 2D Layered Mxenes widely applied to energy storage owing to their remarkable electrical conductivity and adjustable interlamellar spacing, the synthesis process is time-consuming and hazardous. Therefore, Non-layered transition metal carbides (TMC) have gradually become a research hotspot. Herein, a facile two-step method is reported to synthesize the V 8 C 7 nanoparticles grown in situ in carbon microspheres (V 8 C 7 @CMs). The V 8 C 7 @CMs provide high specific capacity (774 mAh g−1 after 330 cycles at 0.1 A g−1) in half cell. The long cycle stability with extraordinary rate capability (150 mAh g−1 after 5000 cycles at 1 A g−1, 100 mAh g−1 - 13000 cycles - 2 A g−1, and 70 mAh g−1 - 20000 cycles-5 A g−1) can be demonstrated. In order to realize the construction of high-performance LIHCs, it is also very important to design the cathode materials reasonably. So, the cathode material, nitrogen doped grapefruit peel biochar (NGPB), with outstanding rate performance and superior cycle stability, was designed and synthesized by the method of calcination. The performance tests indicates that the specific capacity is kept at 125 mAh g−1 after 2000 cycles at 1 A g−1, 120 mAh g−1-2000 cycles-2 A g−1 and 115 mAh g−1-2000 cycles-5 A g−1. Then, the constructed V 8 C 7 @CMs//NGPB-2 LIHCs demonstrates high power density (PD) (9358 W kg−1), energy density (ED) (95.55 Wh kg−1) and excellent long cycle stability (a capacity retention rate of 74.7% after 10,000 cycles at 0.1 A g−1, 77%−5000 cycles-1 A g−1). Based on the above research, it is found that the key to realize high-performance LIHCs is to develop long-cycle stable and super rate capability anode materials. [Display omitted] • Non-layered V 8 C 7 @CMs has remarkable long cycle stability and superior rate capability. • NGPB-2 has high specific surface area of 3883.2 m2 g−1 and superior rate capability. • The asymmetric supercapacitor shows 91 Wh kg−1 maximum energy density at 400 W kg−1 [ABSTRACT FROM AUTHOR]

First-principles calculations have been performed to study the structural, electronic and magnetic properties of η -carbides M 3 W 3 C depending on the type of 3 d transition metal (TM). The mechanical properties, such as elastic moduli, mechanical stability and ductility as well as formation enthalpy, were predicted and compared with those for binary M x C y carbides. We find that the bulk, shear and Young’s modules have parabolic dependences on 3 d TM with their maximum values for Fe 3 W 3 C. As follows from the elastic constants and moduli, all η -carbides should be more ductile than typical binary carbides with strong covalent M-C bonds. We predict M 3 W 3 C to be stable and discuss their precipitation sequences in comparison with binary carbides MC, M 3 C, M 6 C, M 7 C 3 , M 5 C 2 and M 23 C 6 . Depending on the 3 d TM, the ternary M 3 W 3 C carbides demonstrate a variety of magnetic structures which may be nonmagnetic or may consist of ferromagnetic tetrahedra, which are coupled ferromagnetically or antiferromagnetically. [ABSTRACT FROM AUTHOR]

(Ti 1-x W x )C solid solutions (x = 0.05, 0.15, 0.25, 0.35) were synthesized by carbothermal reduction and then were used as hard phases to prepare (Ti,W)C-Ni 3 Al cermets by vacuum sintering. (Ti,W)C-Ni 3 Al cermets showed weak core-rim structure carbide particles embedded in Ni 3 Al binder. As W content in (Ti,W)C increased, core-rim structure of carbide particles got weaker and the contrast of particles lowered down in SEM-BSE morphologies. Furthermore, the densification of cermets was promoted with W content in solid solution increasing, meanwhile TRS and toughness of cermets were improved obviously. In this paper, the wettability of molten metal on different group transition metal carbides was discussed in detail based on valence-electron configurations (VECs) of carbides. [ABSTRACT FROM AUTHOR]

As a typical kind of two-dimensional transition metal carbides, nitrides and/or carbonitrides (MXene), Ti 3 C 2 T x has attracted extensive attention in optoelectronic field owing to their outstanding thermal, optoelectronic, and nonlinear optical properties. Ti 3 C 2 T x has been widely used as saturable absorber (SA) for achieving ultrafast pulses, whereas the influence of recovery time on its nonlinear optical properties as SA in laser needs further exploration. Herein, the ultrafast dynamics and nonlinear optical properties of Ti 3 C 2 T x are investigated by the methods of transient absorption and balanced twin-detector measurements. According to the experimental results, Ti 3 C 2 T x has a bleaching recovery time more than 160 ps, resulting in a low saturation intensity. The prepared Ti 3 C 2 T x is utilized as SA to achieve Q-switched pulses at 1- and 1.5- μ m bands. This study demonstrates that ultrafast dynamics has a significant impact on adjusting and optimizing nonlinear optical parameters of MXenes, as well as designing new photonic devices. • Optical properties and applications of Ti 3 C 2 T x as saturable absorber (SA) in 1- and 1.5- μ m lasers were studied. • Effect of carrier dynamics of Ti 3 C 2 T x on saturable absorption performance was discussed. • Ti 3 C 2 T x as SA in lasers was quantitatively analyzed, benefiting for realizing customized SA. • Large-energy Q-switched pulses were realized in 1- and 1.5- μ m bands owing to low saturable intensity. [ABSTRACT FROM AUTHOR]

A new family of two-dimensional (2D) transition metal carbides, carbonitrides, and nitrides that were discovered and developed at Drexel University in 2011, which is called MXene and is applicable for several critical applications. These so-called MXene structures possess excellent properties e.g., rich surface chemistry, electronic structures, high electrical conductivity, hydrophilicity, thermal and mechanical stability, and large specific surface area, which have attracted tremendous attention. This review article will focus on some most recent progress and review comprehensively their fabrication methods and compositing with polymers and metals. A major part has been associated with the electrochemical applications, medical, flame retardance effect in a polymer matrix, and electromagnetic shielding properties. In addition, briefly, we will delve into a brief discussion on the current limitations, and future research needs, along with the various corresponding challenges in order to provide a better understanding of these new 2D materials. [ABSTRACT FROM AUTHOR]

MAX phase materials, the precursors of MXenes (2D transition metal carbides, carbon nitrides, and nitrides), have become increasingly popular in electrochemical applications. In this study, we have successfully prepared Ti 2 SnC with high lithium capacity via the in-situ formation of SnO 2. Results show that there are TiC nanowhiskers and SnO 2 inside the Ti 2 SnC MAX calcined at 800 ℃, and the initial specific capacity could reach 377 and 371 mAh·g−1 at high current densities of 400 mA·g−1 and 1.0 A·g−1, respectively. These values are higher than those of most MAX phase materials reported in previous studies, such as Ti 3 SiC 2 and Nb 2 SnC, but the stability and rate performance are inferior, which is a direction for the future. This paper provides a new pathway for the application of MAX phases in electrochemistry, which has more in-depth application prospects. ● Ti 2 SnC with in-situ formation of SnO 2 was successfully prepared by a calcination method. ● The Ti 2 SnC layered structure slows down the volume expansion of in-situ prepared SnO 2. ● This anode material performed a better specific capacitance, arriving at 377 mAh/g at the current density of 1.0 A/g. [ABSTRACT FROM AUTHOR]

Transition metal carbide is being used as an emerging high-capacity anode material for the next-generation potassium ion batteries (PIBs). Herein, a general method was introduced for the preparation of nanocomposites from metal–organic frameworks (MOFs) coated with ammonium ferric citrate. A novel composite material of Fe 3 C nanoparticles was designed and prepared by pyrolysis of MOF, and embedded in graphitic carbon as a PIB anode (Fe 3 C@MOF–C/N). The Fe 3 C particles were encapsulated in an N-doped carbon shell with a hierarchical porous carbon network. N-doped porous carbon exhibited a large specific surface area and abundant carbon edge defects, which led to the increase in the number of exposed active sites, facilitating the adsorption of potassium ions. As a result, the prepared carbon material shows high structural stability, electrical conductivity, and proton conductivity. As a PIB anode, Fe 3 C@MOF–C/N-1 shows a high capacity of 294 mAh g−1 over 1000 cycles at 200 mA g−1, revealing its potential application as carbon material in PIB anodes. Fe 3 C in the formation of nanocrystallization is encapsulated in the separate N-doping carbon, and shows remarkably enhanced electrochemical potassium ion storage performance. [Display omitted] • ZIF-8 derived porous carbon core provide space for s physical adsorption of the PIBs. • Capacity of 294 mAh g−1 is remained for Fe 3 C@MOF–C/N-1 at 200 mA g−1 after 1000 cycles. • Fe 3 C in the formation of nanocrystallization is encapsulated in the separate N-doping carbon. • The Fe 3 C@MOF–C/N-1 anodes exhibit enhanced cyclic stability and rate performance. [ABSTRACT FROM AUTHOR]

• Ordered mesoporous carbon/Molybdenum carbide nanocomposite was prepared via a hydrothermal reaction with a hard template. • The OMC/Mo 2 C nanocomposite shows excellent electrochemical properties due to the synergistic effect between Mo 2 C and OMC. • The OMC/Mo 2 C nanocomposite exhibits a specific capacitance of 1718 F g−1 at 1 A g-1 current density. • The OMC/Mo 2 C nanocomposite based asymmetric supercapacitors manner high energy and power densities. [Display omitted] Supercapacitors are a different promising technique to satisfy the rising demand for energy storage systems. Introducing an economical and highly active electrocatalysts is crucial to exploit clean and environmental-friendly energy technology in the future. We have successfully manufactured a supercapacitor based on ordered mesoporous carbon/ molybdenum carbide (OMC/Mo 2 C) nanocomposite. OMC has been chosen as a substrate due to its conductivity, favorable physical strength, high flexibility, and light structure. The OMC/Mo 2 C nanocomposite electrode performed exceptionally well from electrochemical perspective, with a high capacity of 1718 F g−1 at 1 A g−1 current density. It was seen that the capacitance retention rate could still reach 90.3% after 5000 cycles, indicating that the OMC/Mo 2 C nanocomposite electrode has excellent stability. Moreover, the assembled OMC/Mo 2 C//AC asymmetric supercapacitor exhibits capacitance of 299.4 F g−1 at a current density of 1 A g−1, and a large energy density of 106.4 Wh kg−1 at a power density of 800 W kg−1, by exceptional cycling stability with 90% capacity maintenance after 5000 cycles. The research findings can be applied in the development of high-performance energy storage devices based on carbides of transition metals. [ABSTRACT FROM AUTHOR]

Abstract: The biocompatibility and microstructural variation of Fe–Al–Mn (FAM)-based alloys have been investigated clearly. The ((Fe,Mn)3AlC x ) carbide (κ′-carbide) and Fe0.6Mn5.4C2 carbide (κ-carbide) as well as Cr7C3 (Cr-carbide) were formed on FAM alloy, following phase transformation by heat treatment and surface functionalization. These carbides have important role in forming nanostructure and oxidation layer. Moreover, it was found that the albumin adsorbed onto the surface increased with increasing nano-metal carbides. Therefore, heat treatment and surface functionalization such as electro-discharging and anodization not only generates a nanostructural precipitates, but also converts the alloy surface into a nanostructured oxide surface, then increasing the alloy biocompatibility. [ABSTRACT FROM AUTHOR]

Abstract: The study of partial oxidation of methane (POM) over bimetallic nickel- or copper-actinide oxides was undertaken. Binary intermetallic compounds of the type AnNi2 (An=Th, U) and ThCu2 were used as precursors and the products (2NiO·UO3, 2NiO·ThO2 and 2CuO·ThO2) characterized by means of X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and temperature-programmed reduction. The catalysts were active and selective for the conversion of methane to H2 and CO and stable for a period of time of ≈18h on stream. The nickel catalysts were more active and selective than the copper catalyst and, under the same conditions, show a catalytic behaviour comparable to that of a platinum commercial catalyst, 5wt% Pt/Al2O3. The catalytic activity increases when uranium replaces thorium and the selectivity of this type of materials is clearly different from that of single metal oxides and/or mechanical mixtures. The good catalytic behaviour of the bimetallic copper- and nickel-actinide oxides was attributed to an unusual interaction between copper or nickel oxide and the actinide oxide phase as showed by H2-TPR, XPS and Raman analysis of the catalysts before and after reaction. [Copyright &y& Elsevier]

Abstract: Although no detailed study on the Cr solubility in WC exists the compilation on the various C–Cr–W phase diagrams suggests this behaviour. In order to prove this and to estimate the diffusivity of Cr in WC we prepared diffusion couples of the type Cr3C2–WC by joining and annealing polished fully dense counterparts of the two carbides (temperature range 1550–1750°C). After thermal treatment the diffusion couples were cut, polished and investigated by metallography. For the measurement of the diffusion profiles the couples were subjected to WDS-EPMA (Cameca SX 100 microprobe). W, Cr, and C concentration profiles were obtained from line scans performed perpendicular to the interface. The analysis of diffusion couples of WC contacted to other carbides used for doping of hardmetals (VC, TaC, NbC, and TiC) did not yield perceptible solubility of the respective metals in WC with respect to the detection limit of EPMA. From the Cr diffusion profiles a diffusion coefficient of Cr in WC of approximately D =1.70–2.20×10−11cm2/s and an activation energy of E A =0.75eV was estimated. In addition the composition of the ternary phase (W,Cr)2C in equilibrium with WC and Cr3C2 could be measured. For example, in couples annealed at 1750°C the composition reaches from (W0.5Cr0.5)2C (in equilibrium with WC) to (W0.2Cr0.8)2C (in equilibrium with Cr3C2). With the results obtained from the analysis of diffusion couples, the Cr uptake of WC powder as a function of grain size, time and temperature was calculated. Cr saturation in idealised spherical particles of 1μm occurs only within a few minutes. [Copyright &y& Elsevier]

Abstract: WC–Al2O3 composite powder potentially could be synthesized through milling of WO3–C–2Al mixture. High temperature resulted from reduction of WO3 by Al, activates the reduction reaction of WO3 by C and brings about carbon deficiency in the system which consequently causes the formation of undesirable W2C phase. Hence, addition of excess amounts of C becomes necessary. The aim of the present study has been to find out some appropriate routes for the fabrication of WC–Al2O3 composite powder from WO3–2Al–C mixtures in such a way that the formation of W2C is prevented. Results of high energy milling showed that the mode of reaction in WO3–2Al–C mixture is MSR (mechanically induced self-propagating reaction). In this system, evolution of CO gas and high value of C loss were evidences for the need of excess C. For samples produced via suggested routes, no CO evolution was observed and the amounts of total carbon were constant. These observations showed that the proposed routes have been capable of producing WC phase without the presence of W2C. Mechanism of the reactions in each route has been discussed. [Copyright &y& Elsevier]

Abstract: Preparation of the ternary carbide Ti3AlC2 was conducted by combustion synthesis in the mode of self-propagating high-temperature synthesis (SHS) from both the elemental powder compacts of Ti:Al:C=3:1:2 and the Al4C3-containing samples compressed from the powder mixtures of Ti/Al/C/Al4C3 with Al4C3 content ranging from 1.85 to 5.56mol%. The reactant compact with 5.56mol% Al4C3 represents a composition of 3Ti+1.25C+0.25Al4C3, within which Al4C3 serves as the only source of Al. Effects of the Al4C3 addition and sample green density were studied on the combustion characteristics and product compositions. Due to formation of liquid Ti–Al melt and growth of the Ti3AlC2 grains, the powder compact was subjected to substantial deformation during the SHS process. With an increase in the Al4C3 content, the reaction temperature and flame-front propagation velocity were reduced, but the degree of Ti3AlC2 formation was improved. In addition to Ti3AlC2 formed as the dominant phase, the XRD analysis identified two secondary phases TiC and Ti2AlC in the synthesized products. Formation of Ti3AlC2 was also enhanced by increasing the sample green density. For the elemental powder compacts, the content of Ti3AlC2 yielded in the products increased from 50.5 to 73.2wt% with increasing sample density from 45 to 65% TMD. It was found that under a constant compaction density of 60% TMD, the product composed of 75.3wt% Ti3AlC2 was produced from the 5.56mol% Al4C3-containing sample, in comparison with only 61wt% Ti3AlC2 from the elemental reactant. Moreover, as the sample density further increased to 70% TMD, the yield of Ti3AlC2 approaching 80wt% was obtained. [Copyright &y& Elsevier]

The development of novel transition metal carbides for improved hard coating technologies requires a detailed understanding of the factors influencing their stability and mechanical performance. To this end, we carried out first principles calculations based on density functional theory to tabulate the electronic structures, formation energies, and phonon dispersion curves of 3d transition metal carbides adopting zincblende, rocksalt, and cesium chloride structures. By analyzing the corresponding results, we outline a theoretical framework that describes how valence electron concentration and bonding configuration control the stability of these compounds. Many early transition metal carbides are predicted to be stable in the rocksalt and zincblende structures, enabled by filled bonding states, whereas the cesium chloride structure shows persistent instability. For compounds that are predicted to be stable, mechanical properties were investigated through calculation of elastic tensors, from which observable properties including Vicker's hardness and ductility were derived. A robust mechanical performance is shown to be correlated with complete filling of bonding orbitals as illustrated for rocksalt TiC and VC, which have calculated hardnesses of 25.66 and 22.63 GPa respectively. However, enhanced ductility and toughness can be achieved by allowing partial occupation of the antibonding states as in CrC, which has a relatively low Pugh's ratio of 0.51. [Display omitted] • Early 3d transition metal carbides show robust stability and high hardness. • Complete filling of bonding orbitals is crucial to maintain stability. • Partial antibonding contributes to decreased hardness but enhanced ductility. • Overoccupied antibonding orbitals cause instabilities in the rocksalt structure. • Jahn-Teller distortions cause instabilities in the zincblende structure. [ABSTRACT FROM AUTHOR]

• Multiscale porous MXene films are sequentially formed by oxidation and pH-controlled crumpling. • Mesopores generated from partial oxidation process greatly facilitate the ion diffusion. • Macropores formed by crumpling would prevent the restacking problem of MXene. • Increased porosity and specific surface area of porous MXene result in high capacitance in supercapacitors. [Display omitted] MXene, an example of two-dimensional (2D) transition metal carbides, is a promising electrode material for batteries and supercapacitors because of its excellent electrochemical properties derived from transition metal carbide/nitride constituents and its high electrical conductivity. However, similar to other 2D nanomaterials, MXene-based electrodes have a notable shortcoming of reduced specific surface area and reduced ion diffusion due to the self-restacking of MXene nanosheets. Here, to overcome these limitations, we present a novel method to create oxidized-co-crumpled multiscale porous architectures of MXene by a sequential process consisting of partial oxidation by hydrogen peroxide and then flocculation in acid. These treatments result in simultaneous generation of mesopores by oxidation and macropores caused by structural crumpling. This oxidized-co-crumpled MXene has a five times larger specific surface area (72 m2/g) than pristine MXene. In addition, the capacitance performance (307 F/g at 20 mV/s under 1 M H 2 SO 4) and the capacitance at a higher scan rate (225 F/g at 100 mV/s) are improved. Additionally, after 6000 cycles, 87.6% of the capacitance is retained. Such an improvement in the properties is attributed to the structural advantages of the multiscale porous oxidized-co-crumpled MXene, wherein ion diffusion through mesopores is facilitated, while the crumpled macropores prevent re-stacking. Overall, this study demonstrates a promising strategy to create MXene-based high performance electrode materials for a variety of electrochemical applications. [ABSTRACT FROM AUTHOR]

• Simple chemical reduction employed to form the Mo 2 C and Mo 2 C-CNTs nanostructures. • For the first time, Mo 2 C-CNTs blended PEDOT:PSS comprised devices were constructed. • Mo 2 C-CNTs@PEDOT:PSS layer comprised PSC produced an enhanced efficiency of ~11.98%. • High sensitivity of 3.56 mA/Gy·cm2 sensed for Mo 2 C-CNT@HTL involved X-ray detector. Transition metal carbide (Mo 2 C) and carbon nanotubes (CNTs) have been used to modify the hole transport layers (HTLs) in perovskite solar cells (PSCs) and photodetectors due to their high metallic conductivity, superior charge extraction probability, tunable work function, and high reliability. Here, for the first time, Mo 2 C, CNTs, and a Mo 2 C-CNT hybrid were blended with a PEDOT:PSS HTL in an ITO/HTL/CH 3 NH 3 PbI 3 /PCBM/LiF/Al device architecture. The power conversion efficiency of the resulting PSC improved to 11.98% with the use of Mo 2 C-CNT@PEDOT:PSS HTL compared to the pure PEDOT:PSS (9.17%), Mo 2 C@PEDOT:PSS (9.82%) and CNT@PEDOT:PSS (10.61%) HTLs. The PSC performance of device prototypes with different loadings (1, 1.5, and 2 wt%) of the Mo 2 C@CNT nanocomposite in the HTL was also examined. The prepared Mo 2 C-CNT@PEDOT:PSS HTL-based device was then employed as X-ray photodetector, achieving a maximum sensitivity of 3.56 mA/Gy·cm2. Our findings illustrate the potential for the use of MXene-CNT nanocomposites with a perovskite layer to enhance the efficacy of solar cells and photodetectors. [ABSTRACT FROM AUTHOR]

Hydrogen is considered as a potential alternate energy to fossil fuels in the future. However, no matter in hydrogen production, storage, transportation or application, there are still huge challenges hindering the development of hydrogen energy. Transition metal carbides (TMCs) and nitrides (TMNs) have been received widespread attention in electrocatalytic water splitting to obtain hydrogen due to its noble-metal-like characteristic. In this review, we make a basic introduction including the structure, physical properties, and common prepared method of TMCs/TMNs. Then briefly introduce the reaction mechanism and evaluation criteria of electrochemical water splitting. After that, this paper reviews the recent progress of in the development of transition metal carbides and nitrides which discussion focused on the different modification methods such as nanostructuring, heteroatom doping, heterostructure construction and defect engineering. Furthermore, this review summarizes the electrocatalytic performances of recent reported TMCs and TMNs in hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and overall water splitting. Finally, we conclude several effective strategies on the catalysts design and raise challenges remained on the electrocatalytic water splitting. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we report on the synthesis and oxidation behavior of Ti2InC, Zr2InC, (Ti0.5,Hf0.5)2InC and (Ti0.5,Zr0.5)2InC. The oxidation kinetics were studied thermogravimetrically in air in the 400–700°C temperature range. With the exception of Ti2InC, the oxide layers formed failed to offer any oxidation resistance at 400°C or higher temperatures. The reaction products are In2O3, in which some transition metal ions are probably dissolved, and the transition metal oxides. The latter are either amorphous or nanocrystalline. In the case of Ti2InC, a protective oxide was formed at 500°C. However, at higher temperatures, after an incubation period, catastrophic oxidation ensued. In all cases, the oxidation occurred by the inward diffusion of oxygen. [Copyright &y& Elsevier]

Tunable Electromagnetic Interference (EMI) shielding behaviors of 2D MXene (Nb 2 CT x) were explored via different exfoliation conditions. Stacked, lamellar few-layer, oxygen-related surface functional groups, and structural defects along with oxidative products of Nb 2 CT x were identified by tuning chemical etching conditions during one-step exfoliation process. Exfoliation of Nb 2 CT x with a tightly packed stacked structure remarked at lower etching times. The unpacking of Nb 2 CT x into lamellar morphology followed by separated few-layer Nb 2 CT x remarked at moderate etching time, whereas structural misalignment, defects, and oxidation of Nb 2 CT x occurred during prolonged chemical etching times. Synergistic effect of one-step extracted few-layers and lamellar structured Nb 2 CT x favorably enrich the assembly of multiple electrical conductive pathways responsible for absorption dominated EMI shielding performance in X- and Ku-band region. The assembled wax nanocomposites with 80% of Nb 2 CT x loading exfoliated at 100 h etching time at a thickness of 1 mm exhibited EMI shielding effectiveness of about 44.09 ± 1.99 dB at 12 GHz, and its EMI attenuation mechanism explained by conduction and eddy current loss. The combined action of few-layer and lamellar Nb 2 CT x nanostructures could be interesting for making novel shielding materials; open a new avenue for niobium series in the MXene family for elaborated applications. • Investigation on one step exfoliation of few-layer transition metal carbide (Nb2CTx) MXene by tuning exfoliation conditions. • The Nb 2 CT x wax nanocomposites exhibited EMI shielding effectiveness of about 44.09±1.99 dB at 12 GHz. • Synergistic action of few-layer and laminar Nb 2 CT x favorable conducting network lead higher absorbing capacity of EM waves. [ABSTRACT FROM AUTHOR]

• Nitrogen and sulfur co-doping strategy increases the N 2 fixation yield of Ti 3 C 2 T x by five times. • Synergistic effect of co-doping regulates the electron configuration and accelerates the reaction kinetics. • NS-Ti 3 C 2 T x achieves excellent recyclability and long-term stability in acidic electrolyte. • This work opens a new research approach for high-performance catalysts in energy storage applications. [Display omitted] High-polluting industrial ammonia synthesis runs counter to the intentions of a low-carbon society. In contrast, the electrocatalytic nitrogen reduction reaction (NRR) is expected to provide fascinating and broad prospects for green ammonia synthesis, which urgently requires efficient and low-cost catalysts. Although it has been proven that two-dimensional (2D) transition metal carbides and carbonitrides (MXenes) have great potential for NRR, there is still need to further improve their activity. In this work, a co-doping strategy was employed to design the electronic configuration and structural mechanic of Ti 3 C 2 T x catalysts for efficient NRR. As expected, the synergistic effect of N and S dopants in Ti 3 C 2 T x (NS-Ti 3 C 2 T x) significantly improves the electron/ion transport capacity and increases the catalytic active sites. Specifically, the as-prepared NS-Ti 3 C 2 T x nanosheets demonstrated an excellent electrocatalytic stability with NH 3 yield of 34.23 μg h−1 mg−1 cat at −0.55 V vs. RHE, and a Faraday efficiency of 6.6% in 0.05 M H 2 SO 4. Therefore, this work opens up a new research approach for preparing high-performance catalysts for energy storage applications through efficient nitrogen fixation technology. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) transition metal carbides (MXenes) exhibit great potential application in the microwave absorption (MA) field due to their layered structure, excellent dielectric loss and adjustable layer spacing. Herein, Nb 2 O 5 with different morphologies (columnar and irregular granular) was successfully synthesized in situ and implanted between the layers of a Nb 2 CT x MXene through a rapid microwave-assisted hydrothermal method. Newly formed Nb 2 O 5 and Nb 2 CT x from an incomplete reaction composed the Nb 2 O 5 /Nb 2 CT x hybrids. Compared with that for the pure Nb 2 CT x , the Nb 2 O 5 /Nb 2 CT x composites showed enhanced MA performance, especially the Nb 2 O 5 /Nb 2 CT x composites with columnar Nb 2 O 5 (c-Nb 2 O 5 /Nb 2 CT x). The minimum reflection loss (RL) value reached −44.1 dB at 2.8 GHz with a thickness of 5 mm, indicating that approximately 99.99% of the incident microwaves were absorbed. The special morphology of the columnar Nb 2 O 5 , the increased lamellar spacing of the Nb 2 CT x , and the optimized impedance matching characteristic are all important factors that contributed to the enhanced MA performance. • Controllable morphology regulation of Nb 2 O 5 was achieved through oxidation of Nb 2 CT x. • Nb 2 O 5 with a columnar structure could supply expanded spacing between Nb 2 CT x layers. • Impedance matching and multiple scattering were enhanced for Nb 2 O 5 /Nb 2 CT x composites. [ABSTRACT FROM AUTHOR]

Two-dimensional transition metal carbides and nitrides (MXenes) demonstrate excellent performances in various field as a result of their unique surface group structures and high electrical conductivity. In this work, we employ a simple strategy of surface group modification to optimize the semiconductor performance of a high-conductivity Ti 3 C 2 T x film for thermoelectric energy conversion. In the process, the hydrothermal treatment with different concentrations, temperatures, and types of alkali solutions has significant effects on the thermoelectric properties of Ti 3 C 2 T x. As a result, the modified free-standing Ti 3 C 2 T x film maintained its originally high conductivity (1652 S cm−1) and the Seebeck coefficient is improved threefold, leading to an optimized power factor of 44.98 μW m−1K−2 at room temperature. This study provides a new method for the development of the thermoelectric performance of highly-conductive MXene films. Image 1 • The thermoelectric properties of the terminal groups modified Ti 3 C 2 T x film are systematically studied experimentally. • The Seebeck coefficient of the modified Ti 3 C 2 T x film increases by 3 times due to wider band gap. • The modified Ti 3 C 2 T x film still maintains the hig electrical conductivity (1652 S cm-1). [ABSTRACT FROM AUTHOR]

High-entropy (Zr,Ti,Hf,Nb,Ta)C ceramic with single-phase rock salt structure was prepared by spark plasma sintering and their oxidation behavior was investigated at 1200 °C water vapor atmosphere. Results indicate that high-entropy carbides exhibit high oxidation resistance with a small mass gain per unit area of 6.6 × 10−2 kg/m2 after oxidation for 5 h. The parabolic rate constant k p of (Zr,Ti,Hf,Nb,Ta)C ceramic is almost two order of magnitude lower than that of ZrC ceramic. The high oxidation resistance is generally ascribed to the large lattice distortion and the formation of dense oxide scale which significantly suppressed the metal elements and H 2 O diffusion. • High-entropy transition metal carbides exhibit high oxidation resistance. • Large lattice distortion and the dense oxide scale is responsible. [ABSTRACT FROM AUTHOR]

Similar to graphene, two-dimensional (2D) transition metal carbides and nitrides (MXenes) have been demonstrated great potential in the electrochemical energy storage owing to their excellent hydrophilicity and conductivity, large specific capacitance and excellent electrochemical performance, etc. The combination of MXene and graphene can effectively prevent the restacking of graphene and MXene, which greatly improve the specific surface area and specific capacity of MXene and graphene. However, the large-scale production of MXene/graphene materials through low-cost and simple synthetic route is a big challenge. In this review, we firstly review recent synthesis methods of Ti 3 C 2 MXene/graphene composites and the related mechanisms. Subsequently, the progress in the energy storage applications of the composites are summarized, including supercapacitors, lithium-ion batteries, lithium-sulfur batteries, etc. Finally, the current existing problem and prospects of the MXene/graphene composites are discussed, which will provide a reference for the design and preparation of high-performance MXene-based energy storage devices. Image 1 • The synthesis methods and related mechanisms of Ti 3 C 2 MXene/graphene composites are summarized. • The applications progress of Ti 3 C 2 MXene/graphene composites in energy storage has been discussed systematically. • The development prospect and perspective of MXene materials in the future are given. [ABSTRACT FROM AUTHOR]

Tungsten oxide (WO 3) as electrode material has the drawbacks including poor rate capability and low capacitance. We firstly report a facile strategy to prepare WO 3 /MXene composite by intimately electrostatic attraction between the positively charged WO 3 nanorods (WNRs) and the negatively charged transition metal carbides (MXene). This type composite shows higher specific capacitance (297 F g−1) compared with pure WNRs (121 F g−1) at a current density of 1 A g−1 in 0.5 M H 2 SO 4 aqueous electrolyte. In addition, the as-prepared composite electrode displays good retention rate (82.2% retention at 5 A g−1) and cyclic stability (73.4% even after 5000 cycles at 4 A g−1). The attractive electrochemical performance of WNRs/MXene may be attributed to the main reasons as follows: The MXene acts as electrons collector effectively improving the electrical conductivity and supplying more electrons to participate redox reactions happened on the surface and interior of WNRs; The electrostatic self-assembly improves the stability of WNRs/MXene. • WO 3 /MXene composite is fabricated by electrostatic attraction for the first time. • The electrostatic self-assembly improves the stability of the composite. • This composite has highly supercapacitive performance. [ABSTRACT FROM AUTHOR]