Partial Atomic Tin Nanocomplex Pillared Few-Layered Ti3C2Tx MXenes for Superior Lithium-Ion Storage

Three-dimensional coated CuNiFe-Prussian blue analogue@MXene heterostructure for capacitive deionization to slow down the damage of MXene by dissolved oxygen

Within the capacitive deionization (CDI) realm, the two-dimensional (2D) layered material T3C2Tx MXene has drawn lots of attention because of its excellent electrical conductivity, reversible ionic intercalation/deintercalation capacity, and extensive active sites. However, the performance of MXene is compromised by the fact that its surface is susceptible to oxidation by dissolved oxygen and has inherent defects of self-stacking. In this paper, CuNiFe-Prussian blue analogue@MXene (CuNiFe-PBA@MXene) with three-dimensional (3D) coated heterostructure is successfully prepared by the in-situ coprecipitation. CuNiFe-PBA is uniformly coated on the MXene surface as a functional layer to avoid the re-stacking of MXene, to enlarge their layer spacing, and to slow down the damage of MXene by dissolved oxygen. Based on a coated structure constructed by a good combination of dual pseudocapacitive materials, the CuNiFe-PBA@MXene electrode has excellent electrochemical performance (250F g-1). The composed MXene//CuNiFe-PBA@MXene hybrid cell in 500 mg/L NaCl has higher desalination capacity (44.94 mg/g), lower energy consumption (0.66 kWh kg-1), and excellent desalination capacity retention (93.46 % after 40 adsorption/desorption cycles). Furthermore, the lower oxidation degree of CuNiFe-PBA@MXene after 40 desalination cycles compared to MXene indicates that the constructed 3D heterogeneous structure can protect MXene and slow down the oxidation of MXene by dissolved oxygen.

Engineering the next generation of MXenes: challenges and strategies for scalable production and enhanced performance

Two-dimensional nanomaterials, such as MXenes, have garnered significant attention due to their excellent properties, including electrical conductivity, mechanical strength, and thermal stability. These properties make them promising candidates for energy storage and catalysis applications. However, several challenges impede their large-scale production and industrial application. Issues such as high production costs, safety concerns related to toxic etching agents, instability in oxidative environments, and the complex synthesis process must be addressed. In this review, we systematically analyze current methodologies for scaling up MXene production, focusing on the synthesis and etching of MAX phases, delamination strategies, and the production of MXene derivatives. We explore strategies for overcoming challenges like aggregation, oxidation, and cost, presenting optimization techniques for enhancing electrochemical performance and stability. The review also discusses the applications of MXenes in batteries and supercapacitors, emphasizing their potential for large-scale use. Finally, we provide an outlook on future research directions for MXene to develop safer and more cost-effective production methods to improve the performance of MXene in order to realize its commercial potential in energy technologies.

h-CoFe2O4/Ti3C2Tx/BNC Hybrid Aerogels with Modulation Impedance Matching for Electromagnetic Wave Absorption and Health Monitoring

Given the limitations of single-function electromagnetic wave-absorbing materials (EWAMs) in meeting the evolving demands of complex usage scenarios, there is a growing need for structure-function integrated composites that offer a combination of microwave absorption, human monitoring, and thermal insulation. This study successfully synthesized two-dimensional (2D) Ti3C2Tx MXene via selective etching of Al from the Ti3AlC2 MAX phase. By introducing MXene into a composite of hydroxylated CoFe2O4 nanoparticles (h-CFO NPs) and bacterial nanocellulose (BNC) to modulate the electromagnetic performance of the EWAMs. The optimized electromagnetic parameters and three-dimensional (3D) porous structure achieve enhanced impedance matching of the wave absorber. The h-CFO/BNC/MXene (h-CFO@CM73) hybrid aerogel demonstrates superior electromagnetic wave absorption (EMWA) performance due to the synergistic effects of conductive loss, magnetic loss, interfacial polarization, and dipole polarization, where a minimum reflection loss (RLmin) of -32.66 dB at a thickness of 4.5 mm, an effective absorption bandwidth (EAB) of 10.70 GHz within the test range, and an EMWA efficiency reaching up to 99.92% were realized. Moreover, the hybrid aerogel presents sensitive sensing capabilities, detecting human joint movements, breathing, and vocalizations. Additionally, the developed hybrid aerogels exhibit commendable thermal insulation and infrared camouflage properties. Consequently, the fabricated multifunctional hybrid aerogel has excellent potential for monitoring care of infants, children, and pregnant women.

Iodine-doped carbon nanotubes boosting the adsorption effect and conversion kinetics of lithium-sulfur batteries

Compared with lithium-ion batteries (LIBs), lithium-sulfur batteries (LSBs), based on electrochemical reactions involving multi-step 16-electron transformations provide higher specific capacity (1672 mAh g-1) and specific energy (2600 Wh kg-1), exhibiting great potential in the field of energy storage. However, the inherent insulation of sulfur, slow electrochemical reaction kinetics and detrimental shuttle-effect of lithium polysulfides (LiPSs) restrict the development of LSBs in practical applications. Herein, the iodine-doped carbon nanotubes (I-CNTs) is firstly reported as sulfur host material to the enhance the adsorption-conversion kinetics of LSBs. Iodine doping can significantly improve the polarity of I-CNTs. Iodine atoms with lone pair electrons (Lewis base) in iodine-doped CNTs can interact with lithium cations (Lewis acidic) in LiPSs, thereby anchoring polysulfides and suppressing subsequent shuttling behavior. Moreover, the charge transfer between iodine species (electron acceptor) and CNTs (electron donor) decreases the gap band and subsequently improves the conductivity of I-CNTs. The enhanced adsorption effect and conductivity are beneficial for accelerating reaction kinetics and enhancing electrocatalytic activity. The in-situ Raman spectroscopy, quasi in-situ electrochemical impedance spectroscopy (EIS) and Li2S potentiostatic deposition current-time (i-t) curves were conducted to verify mechanism of complex sulfur reduction reaction (SRR). Owing to above advantages, the I-CNTs@S composite cathode exhibits an ultrahigh initial capacity of 1326 mAh g-1 as well as outstanding cyclicability and rate performance. Our research results provide inspirations for the design of multifunctional host material for sulfur/carbon composite cathodes in LSBs.

Enhancing Cr(vi) removal performance of Ti3C2T x through structural modification by using a spray freezing method

Structural modification is expected to be a facile way to enhance the adsorption performance of MXene. In this work, the structural modification of Ti3C2T x was carried out by a spray freezing method, and two kinds of nano-structure (spherical and flaky) of Ti3C2T x were prepared by adjusting the solution concentration of Ti3C2T x . Then the Cr(vi) adsorption capacity and removal efficiency of the spherical and flaky Ti3C2T x was investigated, respectively. It is found that flaky Ti3C2T x was produced with a Ti3C2T x concentration of 3 mg mL-1, while spherical Ti3C2T x was obtained with a concentration of 6 mg mL-1. The long diameter of flaky Ti3C2T x is about 8-10 μm, and the specific surface area is 17.81 m2 g-1. While spherical Ti3C2T x had a diameter of about 1-4 μm and a specific surface area of 17.07 m2 g-1. The optimized structure of flaky and spherical Ti3C2T x improves the maximum adsorption capacity by 97% and 33%, respectively, compared with the few-layer Ti3C2T x . The maximum adsorption capacity of flaky Ti3C2T x was 928 mg g-1, while that of spherical Ti3C2T x was 626 mg g-1. The adsorption capacity of both Ti3C2T x structures decreased with the increase of pH, and reached the maximum value at pH = 2; meanwhile, the adsorption capacity of both Ti3C2T x structures increased with the increase of Cr(vi) concentration. The adsorption of Cr(vi) on flaky Ti3C2T x was very fast, reaching equilibrium in 3 min, while spherical Ti3C2T x took 5 min. The adsorption of Cr(vi) on both Ti3C2T x structures belonged to the monolayers, heat-absorbing chemical adsorption, and the diffusion process of Cr(vi) was regulated by the external diffusion and internal diffusion of particles. Its adsorption mechanism was the combination of reductive adsorption and electrostatic adsorption.

Electrochemical biosensor based on RNA aptamer and ferrocenecarboxylic acid signal probe for C-reactive protein detection

Monitoring health-related biomarkers using fast and facile detection techniques provides key physicochemical information for disease diagnosis or reflects body health status. Among them, electrochemical detection of various bio-macromolecules, e.g., the C-reactive protein (CRP), is of great interest in offering potential diagnosis for acute inflammation caused by infections, heart diseases, etc. Herein, a novel electrochemical aptamer biosensor was constructed from Ti3C2Tx MXene and in-situ reduced Au NPs for thiolated-RNA aptamer immobilization and CRP protein detection using Fc(COOH) as the signal probe. The sensory performances for CRP detection were optimized based on working conditions, including the incubation times and the pH. The large surface area offered by Ti3C2Tx MXene and high electrical conductivity originating from Au NPs endowed the as-fabricated aptamer biosensor with a decent sensitivity for CRP in a wide linear range of 0.05-80.0 ng/mL, good selectivity over interfering substances, and a low detection limit of 0.026 ng/mL. Such aptamer biosensors also detected CRP in serum samples using the spike & recovery method with reasonable recovery rates. The results demonstrated the potential of the as-fabricated electrochemical aptamer biosensor for fast and facile CRP detection in practical applications.

Reversible Stacking and Delamination-Regulation of MXene via Controlled Freezing

MXene's configuration, whether it is aggregated or dispersed in a monolayer, determines the specific application areas and even greatly influences the intrinsic properties of MXene. However, how to desirably control MXene's configuration is challenging. Here, a simple, additive-free, chemical reaction-free, and scalable strategy to optionally and reversibly regulate MXene's ordered stacking and delamination of MXene aggregates (AM) is reported. Just by controlled freezing of MXene aqueous dispersions, the aggregation percentage, delamination percentage, and interlayer spacing of AM can be finely tuned. Experimental results reveal that the freezing-induced aggregation and delamination effects can be explained by the squeezing action of growing ice grains on the MXene excluded/concentrated between ice grains and the expanding action caused by the ice formation between AM lamellae, respectively. The dominance between them depends on the freezing parameter-influenced ice nucleation sites, numbers, and ice grain sizes. This work not only contributes to the preparation, storage, and practical applications of MXene, but also opens a new and green avenue for controlling materials' assembly structures.

MXene Composite Electromagnetic Shielding Materials: The Latest Research Status

MXene emerges as a premier candidate for electromagnetic shielding owing to its unique properties as a novel two-dimensional material. Its exceptional electrical conductivity, chemical reactivity, surface tunability, and facile processing render it highly suitable for diverse electromagnetic shielding applications. The research status of MXene and MXene-based electromagnetic shielding materials is systematically discussed in this paper. First, the research status of MXene as a single-component electromagnetic shielding material is briefly introduced. Subsequently, the research status of composite structures constructed by MXene with polymers, carbon derivatives, and ferrites is introduced in detail. Furthermore, the research progress of MXene-based ternary and quaternary composite electromagnetic shielding materials is further focused. Finally, the application of MXene-based composite electromagnetic shielding materials is prospected. A deeper understanding of MXene's electromagnetic shielding properties is facilitated by this paper, providing the direction for the future development of two-dimensional materials in the design and processing of electromagnetic shielding materials.

Unveiling the bifunctional roles of Cetyltrimethylammonium bromide in construction of Nb2CTx@MoSe2 heterojunction for fast potassium storage

Exploring robust electrode materials which could permit fast and reversible insertion/extraction of large K+ is a crucial challenge for potassium-ion batteries (PIBs). Smart interfacial design could facilitate electron/ion transport as well as assure the integrity of electrode. Herein, Cetyltrimethylammonium bromide (CTAB) was found to play bifunctional roles in construction of Nb2CTx@MoSe2 heterostructure. Firstly, functionalization of CTAB on the surface of Nb2CTx could influence the subsequent growth of MoSe2 by electrostatic effect, stereochemical effect and the synergetic Lewis acid-base interaction, leading to the formation of Nb2CTx@MoSe2 with tiled heterostructure. Secondly, the interlayer spacing of Nb2CTx was expanded from 0.77 to 1.21 nm owing to the pillar effect of CTAB. As excepted, the capacity retention was 80 % from 100 mA g-1 (406 mA h g-1) to 1000 mA g-1 concerning rate capability and the specific capacity maintained at 240 mA h g-1 (at 2000 mA g-1) over 300 cycles. The calculated DK values from Galvanostatic intermittent titration technique (GITT) measurement of the titled C-T-Nb2CTx@MoSe2@C electrode is two orders of magnitude larger than the traditional T-Nb2CTx@MoSe2@C electrode, further confirming intimate interface between MoSe2 and Nb2CTx could provide convenient potassium-ion transport channels and fast diffusion kinetics. Finally, ex-situ characterizations at different charging and discharging voltage stages, including ex-situ XRD/Raman/HRTEM/XPS have been carried out to reveal the potassium storage mechanism. This work provides a facile strategy for the regulation of interface engineering by the assist of CTAB which could extend to other MXenes-TMDs (Transition metal dichalcogenides) hybrid electrodes.

The Reverse of Electrostatic Interaction Force for Ultrahigh-Energy Al-Ion batteries

The two-dimensional (2D) MXenes with sufficient interlayer spacing are promising cathode materials for aluminum-ion batteries (AIBs), yet the electrostatic repulsion effect between the surface negative charges and the active anions (AlCl4 - ) hinders the intercalation of AlCl4 - and is usually ignored. Here, we propose a charge regulation strategy for MXene cathodes to overcome this challenge. By doping N and Co, the zeta potential is gradually transformed from negative (Ti3 C2 Tx ) to near-neutral (Ti3 CNTx ), and finally positive (Ti3 CNTx @Co). Therefore, the electrostatic repulsion force can be greatly weakened between Ti3 CNTx and AlCl4 - , or even formed a strong electrostatic attraction between Ti3 CNTx @Co and AlCl4 - , which can not only accommodate more AlCl4 - ions in the Ti3 CNTx @Co interlayers to increase the capacity, but also solve the stacking and expansion problems. As a result, the optimized Al-MXene battery exhibits an ultrahigh capacity of up to 240 mAh g-1 (2-4 times the capacity of graphite cathode, 60-120 mAh g-1 ) and a potential ultrahigh energy density (432 Wh kg-1 , 2-4 times the value of graphite, 110-220 Wh kg-1 ) based on the mass of cathode materials, comparable to LiFePO4 -based lithium-ion batteries (350-450 Wh kg-1 , based on the mass of LiFePO4 ).

Ultrarapid Gelation of Porous Ti3C2Tx MXene Monoliths Induced by Ionic Liquids

Gelation is a promising method to assemble 3D macroscopic structures from MXene sheets for various applications. However, the fine control and scalable manufacturing of 3D MXene monoliths remains a great challenge. Herein, the controllable gelation of Ti3C2Tx MXene initiated by various ionic liquids (ILs) is first proposed, where the IL serve as linkers to bond the nanosheets together through electrostatic and hydrogen bonding interactions, forming 3D monoliths with well-adjustable structure. Furthermore, density functional theory calculations and experiments further reveal the cross-linking effect of different ILs. Typically, 3D porous structure with high specific surface area, suitable pore size, and improved electrolyte affinity is designed through the cross-linking of Ti3C2Tx with 1-vinyl-3-ethylimidazole bromide ([C2VIm]Br-Ti3C2Tx). Due to the strong coupling, the as-synthesized monolith possesses excellent rate performance and high energy density. The methodology is quite flexible, controllable, and universal that provides a new perspective for promoting innovative applications of 2D materials.

3D Lightweight Interconnected Melamine Foam Modified with Hollow CoFe2O4/MXene toward Efficient Microwave Absorption

Considering the increasing severity of electromagnetic wave pollution, the development of high-performance low-filler-content microwave absorbers possessing wide frequency bands and strong absorption for practical applications is a demanding research hotspot. In this study, from the perspectives of the electromagnetic component coordination and structural design, a three-dimensional (3D) interconnected CoFe2O4/MXene-melamine foam (MF) was constructed via simple impregnation and a single freeze-drying step. By changing the absorber (CoFe2O4/MXene) concentration, the pore opening and electromagnetic properties of the 3D foams can be effectively adjusted. When the absorber concentration is sufficiently high to clog the internal pores, the microwave absorption is hindered. When the filler (CoFe2O4/MXene-MF) content is just ∼5.8 wt % (at a density of ∼33.3 mg cm-3), a minimum reflection loss (RLmin) of -72.1 dB is achieved at a matching thickness of 3.32 mm, and an effective absorption bandwidth (4.54 GHz) covering the whole X band is achieved at a thickness of 3 mm. CoFe2O4/MXene-MF, which possesses a 3D porous electromagnetic network structure, optimizes impedance matching and enhances multiple polarization relaxations and reflections/scattering, resulting in superior absorption capabilities. In particular, the continuous network structure ensures the uniform distribution of electromagnetic fields in the microstructure, achieving high absorption at low filler contents. This work provides a reference for subsequent 3D absorber concentration studies and a novel engineering strategy for preparing a low-filler-content, lightweight, and efficient electromagnetic wave absorber, which could be applied in the fields of radar security and information communications.

From Liquid to Solid-State Lithium Metal Batteries: Fundamental Issues and Recent Developments

The widespread adoption of lithium-ion batteries has been driven by the proliferation of portable electronic devices and electric vehicles, which have increasingly stringent energy density requirements. Lithium metal batteries (LMBs), with their ultralow reduction potential and high theoretical capacity, are widely regarded as the most promising technical pathway for achieving high energy density batteries. In this review, we provide a comprehensive overview of fundamental issues related to high reactivity and migrated interfaces in LMBs. Furthermore, we propose improved strategies involving interface engineering, 3D current collector design, electrolyte optimization, separator modification, application of alloyed anodes, and external field regulation to address these challenges. The utilization of solid-state electrolytes can significantly enhance the safety of LMBs and represents the only viable approach for advancing them. This review also encompasses the variation in fundamental issues and design strategies for the transition from liquid to solid electrolytes. Particularly noteworthy is that the introduction of SSEs will exacerbate differences in electrochemical and mechanical properties at the interface, leading to increased interface inhomogeneity-a critical factor contributing to failure in all-solid-state lithium metal batteries. Based on recent research works, this perspective highlights the current status of research on developing high-performance LMBs.

Titanium Carbide (Ti3C2Tx) MXene as Efficient Electron/Hole Transport Material for Perovskite Solar Cells and Electrode Material for Electrochemical Biosensors/Non-Biosensors Applications

Recently, two-dimensional (2D) MXenes materials have received enormous attention because of their excellent physiochemical properties such as high carrier mobility, metallic electrical conductivity, mechanical properties, transparency, and tunable work function. MXenes play a significant role as additives, charge transfer layers, and conductive electrodes for optoelectronic applications. Particularly, titanium carbide (Ti3C2Tx) MXene demonstrates excellent optoelectronic features, tunable work function, good electron affinity, and high conductivity. The Ti3C2Tx has been widely used as electron transport (ETL) or hole transport layers (HTL) in the development of perovskite solar cells (PSCs). Additionally, Ti3C2Tx has excellent electrochemical properties and has been widely explored as sensing material for the development of electrochemical biosensors. In this review article, we have summarized the recent advances in the development of the PSCs using Ti3C2Tx MXene as ETL and HTL. We have also compiled the recent progress in the fabrication of biosensors using Ti3C2Tx-based electrode materials. We believed that the present mini review article would be useful to provide a deep understanding, and comprehensive insight into the research status.

Radiation-Induced Surface Modification of MXene with Ionic Liquid to Improve Electrochemical Properties and Chemical Stability

For the first time, an ionic liquid was grafted onto Ti3C2Tx MXene interlayers (MXene-g-IL) using a radiation technique. The IL was tightly immobilized on the surface of MXene nanosheets via chemical linkage, which exhibited excellent specific capacitance (160 F g-1 at 5 mV s-1) and improved structural stability (maintaining the sheet-like structure for 180 days). The facile, efficient, and scalable synthetic strategy derived from the radiation technique can open a new avenue for covalent functionalization of MXene-based materials and promote their further application.

Structural design and preparation of Ti3C2Tx MXene/polymer composites for absorption-dominated electromagnetic interference shielding

Electromagnetic interference (EMI) is a pervasive and harmful phenomenon in modern society that affects the functionality and reliability of electronic devices and poses a threat to human health. To address this issue, EMI-shielding materials with high absorption performance have attracted considerable attention. Among various candidates, two-dimensional MXenes are promising materials for EMI shielding due to their high conductivity and tunable surface chemistry. Moreover, by incorporating magnetic and conductive fillers into MXene/polymer composites, the EMI shielding performance can be further improved through structural design and impedance matching. Herein, we provide a comprehensive review of the recent progress in MXene/polymer composites for absorption-dominated EMI shielding applications. We summarize the fabrication methods and EMI shielding mechanisms of different composite structures, such as homogeneous, multilayer, segregated, porous, and hybrid structures. We also analyze the advantages and disadvantages of these structures in terms of EMI shielding effectiveness and the absorption ratio. Furthermore, we discuss the roles of magnetic and conductive fillers in modulating the electrical properties and EMI shielding performance of the composites. We also introduce the methods for evaluating the EMI shielding performance of the materials and emphasize the electromagnetic parameters and challenges. Finally, we provide insights and suggestions for the future development of MXene/polymer composites for EMI shielding applications.

In-situ decoration of tin sulfide on Niobium carbide MXene with robust electronic coupling for improved sodium storage performance

Tin sulfide (SnS) has been considered as one of the most promising sodium storage materials because of its excellent electrochemical activity, low cost, and low-dimensional structure. However, owing to the serious volume change upon discharging/charging and poor electronic conductivity, the SnS-based electrodes often suffer from electrode pulverization and sluggish reaction kinetics, thus resulting in serious capacity fading and degraded rate capability. In this work, SnS nanoparticles uniformly distributed on the surface of the layered Niobium carbide MXene (SnS/Nb₂CT_x) were fabricated through a facile solvothermal approach followed by calcination, endowing the SnS/Nb₂CT_x with a three-dimensional interconnected framework as well as fast charge transfer. Benefitting from the excellent electronic/ionic conductivity, efficient buffering matrix, abundant active sites, and high sodium storage activity inherited from the structure design, the robust electronic coupling between SnS nanoparticle and Nb₂CT_x MXene results in excellent electrochemical output, which demonstrates superior reversible capacities of 479.6 (0.1 A/g up to 100 cycles) and 278.9 mAh/g (0.5 A/g up to 500 cycles) upon sodium storage, respectively. The excellent electrochemical performance manifests the promise of the combination of metal sulfides with Nb₂CT_x MXene to fabricate high-performance electrodes for sodium storage.

Recent Advances and Perspectives of Lewis Acidic Etching Route: An Emerging Preparation Strategy for MXenes

Since the discovery in 2011, MXenes have become the rising star in the field of two-dimensional materials. Benefiting from the metallic-level conductivity, large and adjustable gallery spacing, low ion diffusion barrier, rich surface chemistry, superior mechanical strength, MXenes exhibit great application prospects in energy storage and conversion, sensors, optoelectronics, electromagnetic interference shielding and biomedicine. Nevertheless, two issues seriously deteriorate the further development of MXenes. One is the high experimental risk of common preparation methods such as HF etching, and the other is the difficulty in obtaining MXenes with controllable surface groups. Recently, Lewis acidic etching, as a brand-new preparation strategy for MXenes, has attracted intensive attention due to its high safety and the ability to endow MXenes with uniform terminations. However, a comprehensive review of Lewis acidic etching method has not been reported yet. Herein, we first introduce the Lewis acidic etching from the following four aspects: etching mechanism, terminations regulation, in-situ formed metals and delamination of multi-layered MXenes. Further, the applications of MXenes and MXene-based hybrids obtained by Lewis acidic etching route in energy storage and conversion, sensors and microwave absorption are carefully summarized. Finally, some challenges and opportunities of Lewis acidic etching strategy are also presented.

Development of Electromagnetic-Wave-Shielding Polyvinylidene Fluoride-Ti3C2Tx MXene-Carbon Nanotube Composites by Improving Impedance Matching and Conductivity

Absorption-dominated electromagnetic interference (EMI) shielding is attained by improving impedance matching and conductivity through structural design. Polyvinylidene fluoride (PVDF)-Ti₃C₂T_x MXene-single-walled carbon nanotubes (SWCNTs) composites with layered heterogeneous conductive fillers and segregated structures were prepared through electrostatic flocculation and hot pressing of the PVDF composite microsphere-coated MXene and SWCNTs in a layer-by-layer fashion. Results suggest that the heterogeneous fillers improve impedance matching and layered coating, and hot compression allows the MXene and SWCNTs to form a continuous conducting network at the PVDF interface, thereby conferring excellent conductivity to the composite. The PVDF-MXene-SWCNTs composite showed a conductivity of 2.75 S cm^-1 at 2.5% MXene and 1% SWCNTs. The EMI shielding efficiency (SE) and contribution from absorption loss to the total EMI SE of PVDF-MXene-SWCNTs were 46.1 dB and 85.7%, respectively. Furthermore, the PVDF-MXene-SWCNTs composite exhibited excellent dielectric losses and impedance matching. Therefore, the layered heteroconductive fillers in a segregated structure optimize impedance matching, provide excellent conductivity, and improve absorption-dominated electromagnetic shielding.

Ti3 C2 -MXene Partially Derived Hierarchical 1D/2D TiO2 /Ti3 C2 Heterostructure Electrode for High-Performance Capacitive Deionization

Constructing faradaic electrode with superior desalination performance is important for expanding the applications of capacitive deionization (CDI). Herein, a simple one-step alkalized treatment for in situ synthesis of 1D TiO₂ nanowires on the surface of 2D Ti₃ C₂ nanosheets, forming a Ti₃ C₂ -MXene partially derived hierarchical 1D/2D TiO₂ /Ti₃ C₂ heterostructure as the cathode electrode is reported. Cross-linked TiO₂ nanowires on the surface help avoid layer stacking while acting as the protective layer against contact of internal Ti₃ C₂ with dissolved oxygen in water. The inner Ti₃ C₂ MXene nanosheets cross over the TiO₂ nanowires can provide abundant active adsorption sites and short ion/electron diffusion pathways. . Density functional theory calculations demonstrated that Ti₃ C₂ can consecutively inject electrons into TiO₂ , indicating the high electrochemical activity of the TiO₂ /Ti₃ C₂ . Benefiting from the 1D/2D hierarchical structure and synergistic effect of TiO₂ and Ti₃ C₂ , TiO₂ /Ti₃ C₂ heterostructure presents a favorable hybrid CDI performance, with a superior desalination capacity (75.62 mg g^-1 ), fast salt adsorption rate (1.3 mg g^-1 min^-1 ), and satisfactory cycling stability, which is better than that of most published MXene-based electrodes. This study provides a feasible partial derivative strategy for construction of a hierarchical 1D/2D heterostructure to overcome the restrictions of 2D MXene nanosheets in CDI.

The Negative-Charge-Triggered "Dead Zone" between Electrode and Current Collector Realizes Ultralong Cycle Life of Aluminum-Ion Batteries

Typically, volume expansion of the electrodes after intercalation of active ions is highly undesirable yet inetvitable, and it can significantly reduce the adhesion force between the electrodes and current collectors. Especially in aluminum-ion batteries (AIBs), the intercalation of large-sized AlCl₄ ^- can greatly weaken this adhesion force and result in the detachment of the electrodes from the current collectors, which seems an inherent and irreconcilable problem. Here, an interesting concept, the "dead zone", is presented to overcome the above challenge. By incorporating a large number of OH^- and COOH^- groups onto the surface of MXene film, a rich negative-charge region is formed on its surface. When used as the current collector for AIBs, it shields a tiny area of the positive electrode (adjacent to the current collector side) from AlCl₄ ^- intercalation due to the repulsion force, and a tiny inert layer (dead zone) at the interface of the positive electrode is formed, preventing the electrode from falling off the current collector. This helps to effectively increase the battery's cycle life to as high as 50 000 times. It is believed that the proposed concept can be an important reference for future development of current collectors in rocking chair batteries.

Recent progress in use of MXene in perovskite solar cells: for interfacial modification, work-function tuning and additive engineering

The use of perovskites in photovoltaic and related industries has achieved tremendous success over the last decade. However, there are still obstacles to overcome in terms of boosting their performance and resolving stability issues for future commercialization. The introduction of a new 2D material of halide perovskites is now the key advancement in boosting the solar energy conversion efficiency. The implication of a new 2D material (MXene) in perovskite solar cells has been initiated since its first report in 2018, showing excellent transparency, electrical conductivity, carrier mobility, superior mechanical strength, and tunable work function. Based on distinctive features at the hetero-interface, halide perovskite and MXene heterostructures (HPs/Mx) have recently exhibited exceptional improvements in both the performance and stability of perovskite solar cells. Furthermore, the wide families of HPs and MXene materials allow playing with the composition and functionalities of HP/Mx interfaces by applying rational designing and alterations. In this review a comprehensive study of implementing MXenes in perovskite solar cells is presented. First, the implementation of MXenes in perovskites as an additive, and then in charge extraction layers (HTL/ETL), is described in detail. It is worth noting that still only Ti₃C₂T_x, Nb₂CT_x,V₂CT_x MXene is being incorporated into perovskite photovoltaics. Finally, the present obstacles in the use of MXenes in PSCS are discussed, along with the future research potential. This review is expected to provide a complete and in-depth description of the current state of research and to open up new opportunities for the study of other MXenes in PSCs.

Facile Synthesis of Hybrid Anodes with Enhanced Lithium-Storage Performance Realized by a "Synergistic Effect"

Alloying-type anodes including Si- and Sn-based materials are considered the most exploitable anodes for high-performance lithium-ion batteries. However, problems of poor kinetics properties and structural failures such as grain pulverization and coarsening hinder their large-scale application. Herein, SnO₂/Si@graphite hybrid anodes, with nano-SnO₂ and nano-Si thoroughly mixed with each other and loaded onto graphite flakes, have been prepared by a facile ball milling method. Attributed to the "synergistic effect" between SnO₂ and Si, the mechanical stability and kinetics properties can be remarkably enhanced. Furthermore, graphite substrate supplies a fast electrically conductive path and buffers the volume expansion of active particles. Accordingly, SnO₂/Si@graphite delivers 798.9 mAh g^-1 at 200 mA g^-1 and maintains 550.8 mAh g^-1 after 1000 cycles at 1 A g^-1 in half cells. Impressively, a high energy density of 431.4 Wh kg^-1 (based on the mass of anode and cathode) can be obtained in full cells when paired with the NCM622 cathode. This work presents an effective strategy to exploit high-performance alloying-type anodes for LIBs by designing hybrid materials with multiple active components.

A label-free electrochemical immunosensor based on a gold-vertical graphene/TiO2 nanotube electrode for CA125 detection in oxidation/reduction dual channels

A label-free immunosensor was constructed in oxidation and reduction dual channel mode for the trace detection of cancer antigen 125 (CA125) in serum. The gold-vertical graphene/titanium dioxide (Au-VG/TiO₂) electrode was used as the signal-amplification platform, and cytosine and dopamine were used as probes in the oxidation and reduction channels, respectively. VG nanosheets were synthesized on a TiO₂ nanotube array via chemical vapor deposition (CVD), and Au nanoparticles were deeply embedded on the surface and in the root of the VG nanosheets via electrodeposition. The CA125 antibody was then directly immobilized onto the electrode surface, benefitting from its natural affinity for Au nanoparticles. In the oxidation and reduction channels the CA125 antibody-Au-VG/TiO₂ immune electrode had the same response concentration range (0.01-1000 mU∙mL^-1) for the determination of the CA125 antigen. However, the oxidation channel had a higher sensitivity (14.82 μA•(log(mU•mL^-1))^-1 at a working potential of ~ 1.25 V vs. SCE), lower detection limit (0.0001 mU∙mL^-1), higher stability, and lower performance deviation than the reduction channel. This immunosensor was successfully used for CA125 detection in human serum. The recoveries of spiked serum samples ranged from 99.8 ± 0.5 to 100 ± 0.4%. The study on the difference in the sensing performance between oxidation and reduction channels provides a preliminary experimental reference for exploring dual-channel synchronous detection immunosensors and verifying the accuracy of the assay based on dual-channel data, which will promote the development of reliable electrochemical immunosensor technology.

In Situ Architecting Endogenous Heterojunction of MoS2 Coupling with Mo2 CTx MXenes for Optimized Li+ Storage

Endogenous heterojunction of 2D MXenes with unique structure shows inspiring potential in energy applications, which is impeded by complex synthesis method and finite MAX materials. Herein, an in situ hydrothermal strategy is implemented to successfully synthesize unique endogenous hetero-MXenes of amorphous MoS₂ coupling with fluoride-free Mo₂ CT_x (hetero-Mo₂ C) directly from Mo₂ Ga₂ C MAX. The distinctive morphology and heterojunction structure caused by the introduction of MoS₂ endow the hetero-MXenes with extraordinary structural stability and optimized Li⁺ storage mechanism with improved charge transport and lithium ion adsorption capabilities. As a result, hetero-Mo₂ C exhibits excellent electrochemical performance with a high discharge specific capacity of 1242 mAh g^-1 at 0.1 A g^-1 and long cycle stability of 683.9 mAh g^-1 after 1200 cycling. This work provides new insights into rational design of novel MXenes heterojunctions, practically important for the development of MXenes and their applications in high-performance energy storage systems.

Understanding the tunable sodium storage performance in pillared MXenes: a first-principles study

On the basis of first-principles calculations, we studied the influence of the interlayer spacing and stacking modes of pillared MXenes on the sodium storage performance, and predicted the optimum structure for sodium storage.

3D V2CTx-rGO Architectures with Optimized Ion Transport Channels toward Fast Lithium-Ion Storage

Two-dimensional (2D) MXene materials show great potential in energy storage devices. However, the self-restacking of MXene nanosheets and the sluggish lithium-ion (Li⁺) kinetics greatly hinder their rate capability and cycling stability. Herein, we interlink 2D V₂CT_x MXene nanosheets with rGO to construct a 3D porous V₂CT_x-rGO composite. X-ray spectroscopy study reveals the close interfacial contact between V₂CT_x and rGO via electron transfer from V to C atoms. Benefiting from the close combination and optimized ion transport channel, V₂CT_x-rGO offers a high-rate Li⁺ storage performance and excellent cycling stability over 2000 cycles with negligible capacity attenuation. Moreover, it exhibits a dominant mechanism of intercalation pseudocapacitance and efficient Li⁺ transport proved by density functional theory calculation. This rationally designed 3D V₂CT_x-rGO has implications for the study of the MXene composite's structure and energy storage devices with high rate and stability.

MXene/TiO2 Heterostructure-Decorated Hard Carbon with Stable Ti-O-C Bonding for Enhanced Sodium-Ion Storage

Hard carbon (HC) has attracted considerable attention in the application of sodium-ion battery (SIB) anodes, but the poor realistic capacity and low rate performance severely hinder their practical application. Herein we report a solvent mechanochemical protocol for the in situ fabrication of the HC-MXene/TiO₂ electrode by functionalizing MXene to improve the electrochemical performance of the batteries. MXene (Ti₃C₂T_x) with abundant oxygen-containing functional groups reacts with HC particles in the ball milling process to form a Ti-O-C covalent cross-linked HC-MXene composite, in which the edge of the MXene nanosheets is in situ oxidized by air to form TiO₂ nanorods, forming a regular 1D/2D MXene/TiO₂ heterojunction structure. Ti-O-C covalent bonding can protect the heterojunction structures from pulverization and detachment from the current collector during charge/discharge cycles due to sodium-ion intercalation/detachment, thus improving the stability of the electrode structure. Meanwhile, the MXene/TiO₂ heterojunction can form a 3D conductive network and provide more active sites. The resulting HC-MXene/TiO₂ electrode exhibits superior electrode capacity (660 mAh g^-1), making it a promising anode material for SIBs. This simple and efficient method for preparing MXene/TiO₂ heterojunction-decorated HC provides a new perspective on the structural design of MXene and carbon material composites for SIBs.

A Brief Review of the Role of 2D Mxene Nanosheets toward Solar Cells Efficiency Improvement

This article discusses the application of two-dimensional metal MXenes in solar cells (SCs), which has attracted a lot of interest due to their outstanding transparency, metallic electrical conductivity, and mechanical characteristics. In addition, some application examples of MXenes as an electrode, additive, and electron/hole transport layer in perovskite solar cells are described individually, with essential research issues highlighted. Firstly, it is imperative to comprehend the conversion efficiency of solar cells and the difficulties of effectively incorporating metal MXenes into the building blocks of solar cells to improve stability and operational performance. Based on the analysis of new articles, several ideas have been generated to advance the exploration of the potential of MXene in SCs. In addition, research into other relevant MXene suitable in perovskite solar cells (PSCs) is required to enhance the relevant work. Therefore, we identify new perspectives to achieve solar cell power conversion efficiency with an excellent quality-cost ratio.

Commercialization-Driven Electrodes Design for Lithium Batteries: Basic Guidance, Opportunities, and Perspectives

Current lithium-ion battery technology is approaching the theoretical energy density limitation, which is challenged by the increasing requirements of ever-growing energy storage market of electric vehicles, hybrid electric vehicles, and portable electronic devices. Although great progresses are made on tailoring the electrode materials from methodology to mechanism to meet the practical demands, sluggish mass transport, and charge transfer dynamics are the main bottlenecks when increasing the areal/volumetric loading multiple times to commercial level. Thus, this review presents the state-of-the-art developments on rational design of the commercialization-driven electrodes for lithium batteries. First, the basic guidance and challenges (such as electrode mechanical instability, sluggish charge diffusion, deteriorated performance, and safety concerns) on constructing the industry-required high mass loading electrodes toward commercialization are discussed. Second, the corresponding design strategies on cathode/anode electrode materials with high mass loading are proposed to overcome these challenges without compromising energy density and cycling durability, including electrode architecture, integrated configuration, interface engineering, mechanical compression, and Li metal protection. Finally, the future trends and perspectives on commercialization-driven electrodes are offered. These design principles and potential strategies are also promising to be applied in other energy storage and conversion systems, such as supercapacitors, and other metal-ion batteries.

Electrochemical Lithium Storage Performance of Molten Salt Derived V2SnC MAX Phase

MAX phases are gaining attention as precursors of two-dimensional MXenes that are intensively pursued in applications for electrochemical energy storage. Here, we report the preparation of V₂SnC MAX phase by the molten salt method. V₂SnC is investigated as a lithium storage anode, showing a high gravimetric capacity of 490 mAh g^-1 and volumetric capacity of 570 mAh cm^-3 as well as superior rate performance of 95 mAh g^-1 (110 mAh cm^-3) at 50 C, surpassing the ever-reported performance of MAX phase anodes. Supported by operando X-ray diffraction and density functional theory, a charge storage mechanism with dual redox reaction is proposed with a Sn-Li (de)alloying reaction that occurs at the edge sites of V₂SnC particles where Sn atoms are exposed to the electrolyte followed by a redox reaction that occurs at V₂C layers with Li. This study offers promise of using MAX phases with M-site and A-site elements that are redox active as high-rate lithium storage materials.

High Concentration of Ti3C2Tx MXene in Organic Solvent

MXenes are currently one of the most widely studied two-dimensional materials due to their properties. However, obtaining highly dispersed MXene materials in organic solvent remains a significant challenge for current research. Here, we have developed a method called the tuned microenvironment method (TMM) to prepare a highly concentrated Ti₃C₂T_x organic solvent dispersion by tuning the microenvironment of Ti₃C₂T_x. The as-proposed TMM is a simple and efficient approach, as Ti₃C₂T_x can be dispersed in N,N-dimethylformamide and other solvents by stirring and shaking for a short time, without the need for a sonication step. The delaminated single-layer MXene yield can reach 90% or greater, and a large-scale synthesis has also been demonstrated with TMM by delaminating 30 g of multilayer Ti₃C₂T_x raw powder in a one-pot synthesis. The synthesized Ti₃C₂T_x nanosheets dispersed in an organic solvent possess a clean surface, uniform thickness, and large size. The Ti₃C₂T_x dispersed in an organic solvent exhibits excellent oxidation resistance even under aerobic conditions at room temperature. Through the experimental investigation, the successful preparation of a highly concentrated Ti₃C₂T_x organic solvent dispersion via TMM can be attributed to the following factors: (1) the intercalation of the cation can lead to the change in the hydrophobicity and surface functionalization of the material; (2) proper solvent properties are required in order to disperse MXene nanosheets well. To demonstrate the applicability of the highly concentrated Ti₃C₂T_x organic solvent dispersion, a composite fiber with excellent electrical conductivity is prepared via the wet-spinning of a Ti₃C₂T_x (dispersed in DMF) and polyacrylonitrile mixture. Finally, various types of MXenes, such as Nb₂CT_x, Nb₄C₃T_x, and Mo₂Ti₂C₃T_x, can also be prepared as highly concentrated MXene organic solvent dispersions via TMM, which proves the universality of this method. Thus, it is expected that this work demonstrates promising potential in the research of the MXene material family.

MXenes for Solar Cells

Application of two-dimensional MXene materials in photovoltaics has attracted increasing attention since the first report in 2018 due to their metallic electrical conductivity, high carrier mobility, excellent transparency, tunable work function and superior mechanical property. In this review, all developments and applications of the Ti3C2Tx MXene (here, it is noteworthy that there are still no reports on other MXenes' application in photovoltaics by far) as additive, electrode and hole/electron transport layer in solar cells are detailedly summarized, and meanwhile, the problems existing in the related studies are also discussed. In view of these problems, some suggestions are given for pushing exploration of the MXenes' application in solar cells. It is believed that this review can provide a comprehensive and deep understanding into the research status and, moreover, helps widen a new situation for the study of MXenes in photovoltaics.

Electrochemical Performance Enhancement of Micro-Sized Porous Si by Integrating with Nano-Sn and Carbonaceous Materials

Silicon is investigated as one of the most prospective anode materials for next generation lithium ion batteries due to its superior theoretical capacity (3580 mAh g-1), but its commercial application is hindered by its inferior dynamic property and poor cyclic performance. Herein, we presented a facile method for preparing silicon/tin@graphite-amorphous carbon (Si/Sn@G-C) composite through hydrolyzing of SnCl2 on etched Fe-Si alloys, followed by ball milling mixture and carbon pyrolysis reduction processes. Structural characterization indicates that the nano-Sn decorated porous Si particles are coated by graphite and amorphous carbon. The addition of nano-Sn and carbonaceous materials can effectively improve the dynamic performance and the structure stability of the composite. As a result, it exhibits an initial columbic efficiency of 79% and a stable specific capacity of 825.5 mAh g-1 after 300 cycles at a current density of 1 A g-1. Besides, the Si/Sn@G-C composite exerts enhanced rate performance with 445 mAh g-1 retention at 5 A g-1. This work provides an approach to improve the electrochemical performance of Si anode materials through reasonable compositing with elements from the same family.

Structural and chemical interplay between nano-active and encapsulation materials in a core–shell SnO2@MXene lithium ion anode system

Structural and chemical interplay between nano-active and encapsulation materials in a core–shell SnO₂@MXene lithium ion anode system was investigated in detail.

Rational Design of Pillared SnS/Ti3C2Tx MXene for Superior Lithium-Ion Storage

MXenes have been widely explored in energy storage because of their extraordinary properties; however, the majority of research on their application was staged at multilayered MXenes or assisted by carbon materials. Scientifically speaking, the two most distinctive properties of MXenes are usually neglected, composed of large interlayer spacing and abundant surface chemistry, which distinguish MXenes from other two-dimensional materials. Herein, few-layered MXene (f-MXene) nanosheet powders can be easily prepared according to the modified solution-phase flocculation method, completely avoiding the restacking phenomenon of f-MXene nanosheets in preparation and oxidation issues during the storage process. Via further employing the solvothermal reaction and annealing treatment, we successfully constructed pillared SnS/Ti₃C₂T_x composites decorated with in situ formed TiO₂ nanoparticles. In the composites, MXenes can play the role of a conductive network, a buffer matrix for volume expansion of SnS, while the active SnS nanoplates can fully deliver the advantage of high capacity and further induce interlayer engineering of Ti₃C₂T_x during cycling. As a result, the pillared SnS/Ti₃C₂T_x MXene composites exhibit obvious improvement in electrochemical performance. Interestingly, there is an apparent enhancement of capacity at succedent cycling, which can be ascribed to the "pillar effect" of Ti₃C₂T_x MXenes. The efforts and attempts made in this work can further broaden the development of pillared MXene composites.

Dual Immobilization of SnOx Nanoparticles by N-Doped Carbon and TiO2 for High-Performance Lithium-Ion Battery Anodes

The grain aggregation engendered kinetics failure is regarded as the main reason for the electrochemical decay of nanosized anode materials. Herein, we proposed a dual immobilization strategy to suppress the migration and aggregation of SnO_x nanoparticles and corresponding lithiation products through constructing SnO_x/TiO₂@PC composites. The N-doped carbon could anchor the tin oxide particles and inhibit their aggregation during the preparation process, leading to a uniform distribution of ultrafine SnO_x nanoparticles in the matrix. Meanwhile, the incorporated TiO₂ component works as parclose to suppress the migration and coarsening of SnO_x and corresponding lithiation products. In addition, the N-doped carbon and TiO₂/Li_xTiO₂ can significantly improve the electrical and ionic conductivities of the composites, enabling a good diffusion and charge-transfer dynamics. Owing to the dual immobilization from the "synergistic effect" of N-doped carbon and the "parclose effect" of TiO₂, the conversion reaction of SnO_x remains fully reversible throughout the cycling. Thereby, the composites exhibit excellent cycling performance in half cells and can be fully utilized in full cells. This work may provide an inspiration for the rational design of tin-based anodes for high-performance lithium-ion batteries.

Recent advances in MXenes and their composites in lithium/sodium batteries from the viewpoints of components and interlayer engineering

An up-to-date review about MXenes based on their distinguishing properties, namely, large interlayer spacing and rich surface chemistry.

Interfacial superassembly of MoSe2@Ti2N MXene hybrids enabling promising lithium-ion storage

Our work presents an interfacial superassembly by engineering MoSe₂ nanoflowers coupled with ribbon-like Ti₂N MXene frameworks. It can provide a novel synthesis strategy to improve the performance of LIBs.