MOF-Derived ZnS Nanodots/Ti3C2Tx MXene Hybrids Boosting Superior Lithium Storage Performance

Rational Design of a Bilayer Interface for Long-Term Stability of Zn Anodes and MnO2 Cathodes

Understanding the composition-characteristics-performance relationship of the electrolyte-electric double layer-electrode-electrolyte interface (EEI) is crucial to construct stable EEIs for high-performance aqueous Zn-MnO2 batteries (AZMBs). However, the interaction mechanisms in AZMBs remain unclear. This work introduces sodium thioctate (ST) into ZnSO4 electrolyte to construct a stable bilayer EEI on both Zn and MnO2 electrodes. First, zincophilic ST regulates the solvation structure of hydrated Zn2+, suppressing corrosion and the hydrogen evolution reaction. Second, the specific adsorption of ST reconstructs the inner Helmholtz plane, facilitating the desolvation of hydrated Zn2+ and homogenizing charge distribution. Finally, ST molecules undergo reversible polymerization at the interface, forming a stable bilayer EEI with a poly(zinc thioctate) outer layer and a ZnS-organic amorphous inner layer, which ensures uniform zinc-ion flux and enhances mechanical stability. Additionally, the dynamic disulfide bonds in ST further enable self-regulation and self-healing of the interface, mitigating damage during cycling. As a result, the ST-enhanced Zn symmetric battery achieves 7800 cycles at 60 mA cm-2, while the AZMB exhibits only 0.0014% capacity decay over 10 000 cycles at 2000 mA g-1. This bilayer EEI engineering strategy offers effective guidance for the rational design of safe and long-life aqueous zinc-ion batteries.

Synergistic enhancement of the Ag/ZIF-67 cage@MXene 3D heterogeneous structure for ultrahigh SERS sensitivity and stability

There is an urgent need in the in situ field for rapid extraction and analysis of target molecules from irregular surfaces. The application of SERS technology is often limited by low adhesion between precious metal nanoparticles and the substrate and complex fabrication processes. In order to solve this problem, a carbon fiber cloth (CFC) loaded Ag/ZIF-67 cage@MXene 3D detection platform (AZMC) was constructed in this study. The platform takes advantage of the large surface area and defects of MXene flakes to host noble metals, the high carrier transport efficiency between flakes, and van der Waals forces to build highly sensitive and stable composite SERS substrates. The hydrophilicity and subsurface oxidation behavior of MXene make its optoelectronic performance unstable. In this study, the ZIF-67 cage was chemically bonded to MXene through the Co-O-Ti bond, and the ZIF 67@MXene heterojunction was successfully constructed to maintain the optimal photoelectric stability and excellence of MXene. The high performance of the substrate stems from the synergistic effects of charge transfer (CT) and surface plasmon resonance (SPR) of AgNPs and MXene flakes, while the 3D nanocage structure provides additional hotspot regions. Substrate sensitivity was analyzed using rhodamine 6G (R6G) as a probe molecule (detection limit as low as 10-11 M). Notably, the AZMC substrate is highly stable (SERS performance remains essentially unchanged after 45 days of exposure to air). Using this substrate, we also successfully analyzed methylene blue (MB) molecules and Sudan I molecules on apple epidermis, which were successfully detected at concentrations of 0.5 mg L-1 and 1 mg L-1, respectively.

Three-dimensional hollow ZnS/MXene heterostructures with stable Ti-O-Zn bonding for enhanced lithium-ion storage

An effective way to improve the cycling performance of metal sulfide materials is to blend them with conductive materials. In this paper, three-dimensional (3D) hollow MXene/ZnS heterostructures (ZnSMX) were prepared via a two-step process involving hydrothermal and template methodologies. The formation of Ti-O-Zn bonds enables the firm bonding between ZnS nanoparticles and the MXene substrate at heterogeneous interfaces, which can act as "electron bridges" to facilitate electron and charge transfer. Additionally, 3D hollow ZnSMX not only enhances the conductivity of ZnS, enabling rapid charge transfer, but also effectively show restacking of MXene nanosheets to maintain structural stability during the charge/discharge process. More importantly, the 3D porous structure provides ultrafast interfacial ion transport pathways and extra surficial and interfacial storage sites, thus boosting excellent storage performances in lithium-ion battery applications. The 3D ZnSMX exhibited a high capacity of 782.1 mA h g-1 at 1 A g-1 current, excellent cycling stability (providing a high capacity of 1027.8 mA h g-1 after 350 cycles at 2 A g-1), and excellent rate performance. This indicates that 3D ZnS/MXene heterostructures can potentially be highly promising anode materials for high-multiplication lithium-ion batteries.

Controllable Synthesis of Heterogeneous ZnS/SnS2 Encapsulated in Hollow Nitrogen-Doped Carbon Microcubes as Anode for High-Performance Li-ion Capacitors

Li-ion capacitors (LICs) integrate the desirable features of lithium-ion batteries (LIBs) and supercapacitors (SCs), but the kinetic imbalance between the both electrodes leads to inferior electrochemical performance. Thus, constructing an advanced anode with outstanding rate capability and terrific redox kinetics is crucial to LICs. Herein, heterostructured ZnS/SnS2 nanosheets encapsulated into N-doped carbon microcubes (ZnS/SnS2@NC) are successfully fabricated. The sufficient ZnS/SnS2 heterostructure possesses abundant active sites, and the built-in electric field formed at the heterojunction interface can facilitate electron/ion migration. The interconnected hollow carbon layers could reduce the electron transfer resistance effectively and accommodate the volume change of SnS2, thereby maintaining the structural stability. Due to the synergy between multi-components, the ZnS/SnS2@NC anode demonstrates impressive Li storage performance with an excellent cyclic durablity (690 mAh g-1 at 0.5 A g-1 after 600 cycles) and considerable rate capability. Moreover, when matched with active carbon, the ZnS/SnS2@NC based LIC device delivers an admirable energy density of 134.1 Wh kg-1 and a high power output of 11,250 W kg-1, as well as remarkable capacity retention of 73.2 % after 6,000 cycles at 1.0 A g-1. The experimental results demonstrate the significance of optimized heterointerface engineering toward construction of electrode materials with high-performance for Li storage.

Novel in-situ encapsulation of tin phosphide particles in MXene conductive networks as anode materials of the durable sodium-ion battery

Sodium-ion battery (SIB) is one of potential alternatives to lithium-ion battery, because of abundant resources and lower price of sodium. High electrical conductivity and long-term durability of MXene are advantageous as the anode material of SIB, but low energy density restricts applications. Tin phosphide possesses high theoretical capacity, low redox potential, and large energy density, but volume expansion reduces its cycling stability. In this study, tin phosphide particles are in-situ encapsulated into MXene conductive networks (SnxPy/MXene) by hydrothermal and phosphorization processes as novel anode materials of SIB. MXene amounts and hydrothermal durations are investigated to evenly distribute SnxPy in MXene. After 100 cycles, SnxPy/MXene reaches high specific capacities of 438.8 and 314.1 mAh/g at 0.2 and 1.0 A/g, respectively. The capacity retentions of 6.0% and 73.6% at 0.2 A/g are respectively obtained by SnxPy and SnxPy/MXene. The better specific capacity and cycling stability of SnxPy/MXene are attributed to less volume expansion of SnxPy during charge/discharge processes and relieved self-stacking of MXene by encapsulating SnxPy particles between MXene layers. Electrochemical impedance spectroscopy and Galvanostatic intermittent titration technique are also applied to analyze the charge storage mechanism in SIB. Higher sodium ion diffusion coefficient and smaller charge-transfer resistance are obtained by SnxPy/MXene.

In Situ Built ZnS/MXene Heterostructure by a Mild Method for Inhibiting Polysulfide Shuttle in Li-S Batteries

With high specific surface area, excellent polysulfide conversion activity, and fast electron/ion transfer at the interface, MXene-derived heterostructures can be employed as catalysts for lithium-sulfur (Li-S) batteries to accelerate sulfur redox kinetics and suppress shuttle effect. However, the preparation of MXene-derived heterostructures often requires high-temperature reactions, which can easily lead to the oxidation of MXene and sacrifice the electrical conductivity. Herein, a catalytic two-dimensional heterostructure (ZnS/MXene) was successfully synthesized via a mild method. The MXene skeleton retains the original nanosheet structure without oxidation. The in situ-grown ZnS nanospheres prevent the restacking of MXene nanosheets, which not only increases the active sites, but also guarantees channels for the fast passage of lithium ions. The interfacial built-in electric field further promotes electron/ion migration, thereby expediting the polysulfide conversion and suppressing the shuttle effect. Consequently, the batteries using ZnS/MXene modified separators exhibit a high initial discharge capacity of 1230 mAh g-1 at 0.1 C and a low decaying rate of 0.082 % per cycle after 500 cycles at 0.5 C. This work offers a reference for the fabrication of MXene-based heterostructure in Li-S batteries.

Encapsulating Bi Nanoparticles in Reduced Graphene Oxide with Strong Interfacial Bonding toward Advanced Potassium Storage

Bismuth (Bi) is regarded as a promising anode material for potassium ion batteries (PIBs) due to its high theoretical capacity, but the huge volume expansion during potassiation and intrinsic low conductivity cause poor cycle stability and rate capability. Herein, a unique Bi nanoparticles/reduced graphene oxide (rGO) composite is fabricated by anchoring the Bi nanoparticles over the rGO substrate through a ball-milling and thermal reduction process. As depicted by the in-depth XPS analysis, strong interfacial Bi-C bonding can be formed between Bi and rGO, which is beneficial for alleviating the huge volume expansion of Bi during potassiation, restraining the aggregation of Bi nanoparticles and promoting the interfacial charge transfer. Theoretical calculation reveals the positive effect of rGO to enhance the potassium adsorption capability and interfacial electron transfer as well as reduce the diffusion energy barrier in the Bi/rGO composite. Thereby, the Bi/rGO composite exhibits excellent potassium storage performances in terms of high capacity (384.8 mAh g-1 at 50 mA g-1), excellent cycling stability (197.7 mAh g-1 after 1000 cycles at 500 mA g-1 with no capacity decay) and superior rate capability (55.6 mAh g-1 at 2 A g-1), demonstrating its great potential as an anode material for PIBs.

Biomass-derived carbon-sulfur hybrids boosting electrochemical kinetics to achieve high potassium storage performance

Potassium-ion batteries (PIBs) as an emerging battery technology have garnered significant research interest. However, the development of high-performance PIBs critically hinges on reliable anode materials with comprehensive electrochemical performance and low cost. Herein, low-cost N-doped biomass-derived carbon-sulfur hybrids (NBCSHs) were prepared through a simple co-carbonization of the mixture of a biomass precursor (coffee grounds) and sulfur powder. The sulfur in NBCSHs predominantly exists in the form of single-atomic sulfur bonded with carbon atoms (CSC), functioning as main active redox sites to achieve high reversible capacity. Electrochemical evaluations reveal that the NBCSH 1-3 with moderate sulfur content shows significantly improved potassium storage performance, such as a high reversible capacity of 484.7 mAh g-1 and rate performance of 119.4 mAh g-1 at 5 A g-1, 4.5 and 14.7 times higher than that of S-free biomass-derived carbon, respectively. Furthermore, NBCSH 1-3 exhibits stable cyclability (no obvious capacity fading even after 1000 cycles at 0.5 A g-1) and excellent electrochemical kinetics (low overpotentials and apparent diffusion coefficients). The improved performance of NBCSHs is primarily attributed to pseudocapacitance-dominated behavior with fast charge transfer capability. Density functional theory calculations also reveal that co-doping with S, N favors for achieving a stronger potassium adsorbing capability. Assemble K-ion capacitors with NBCS 1-3 as anodes demonstrate stable cyclability and commendable rate performance. Our research envisions the potential of NBCSHs as efficient and sustainable materials for advanced potassium-ion energy storage systems.

Construction of rod-like cobalt-pyridinedicarboxylic acid/MXene nanosheets composites for hydrogen evolution reaction and supercapacitor

Metal-organic frameworks (MOFs) have attracted considerable attention in the field of energy storage and conversion due to their large specific surface area, regulatable pore structure and composition. However, the poor electrical conductivity and few active sites of MOFs impede their application. Herein, highly conductive MXene nanosheets are introduced to modulate the electronic conductivity and structure of rod-like Co-pyridinedicarboxylic acid (Co-PDC), and thus enhancing the electrochemical performance of MOFs. The heterostructural Co-PDC/MXene (CPM) was facily synthesized at room temperature. The as-prepared CPM-30 with 30 % MXene only requires the overpotential of 75.1 mV to achieve a current density of 10 mA cm-2 for hydrogen evolution reaction (HER), and the assembled electrolytic cell with CPM-30 and RuO2 as cathode and anode electrodes can achieve a current density of 10 mA cm-2 at a voltage of 1.65 V. In addition, CPM-10 exhibits a high specific capacitance of 583.1 F g-1 at 0.5 A g-1 and an excellent rate performance of 41.6 % at 50 A g-1. Furthermore, the assembled asymmetric supercapacitor CPM-10//AC exhibited an energy density of 15.55 Wh kg-1 at a power density of 750 W kg-1 and excellent stability with a capacitance retention rate of 95 % after 10,000 cycles. The excellent electrochemical properties of Co-PDC/MXene are attributed to the unique structure and synergistic effect of Co-PDC and MXene.

An effective tellurium surface modification strategy to enhance the capacity and rate capability of Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode material

LiNi0.8Co0.1Mn0.1O2 (NCM) layered oxide is contemplated as an auspicious cathode candidate for commercialized lithium-ion batteries. Regardless, the successful commercial utilization of these materials is impeded by technical issues like structural degradation and poor cyclability. Elemental doping is among the most viable strategies for enhancing electrochemical performance. Herein, the preparation of surface tellurium-doped NCM is done by utilizing the methodology solid-state route at high temperatures. Surface doping of the Te ions leads to structural stability owing to the inactivation of oxygen at the surface via the binding of slabs of transition metal-oxygen. Remarkably, 1 wt% of Te doping in NCM exhibits enhanced electrochemical characteristics with an excellent discharge capacity, i.e., 225.8 mAh/g (0.1C), improved rate-capability of 156 mAh/g (5C) with 82.2% retention in capacity (0.5C) over 100 cycles within 2.7-4.3V as compared to all other prepared electrodes. Hence, the optimal doping of Te is favorable for enhancing capacity, cyclability along with rate capability of NCM.

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.

Versatile MXenes for Aqueous Zinc Batteries

Aqueous zinc-ion batteries (AZIBs) are gaining popularity for their cost-effectiveness, safety, and utilization of abundant resources. MXenes, which possess outstanding conductivity, controllable surface chemistry, and structural adaptability, are widely recognized as a highly versatile platform for AZIBs. MXenes offer a unique set of functions for AZIBs, yet their significance has not been systematically recognized and summarized. This review article provides an up-to-date overview of MXenes-based electrode materials for AZIBs, with a focus on the unique functions of MXenes in these materials. The discussion starts with MXenes and their derivatives on the cathode side, where they serve as a 2D conductive substrate, 3D framework, flexible support, and coating layer. MXenes can act as both the active material and a precursor to the active material in the cathode. On the anode side, the functions of MXenes include active material host, zinc metal surface protection, electrolyte additive, and separator modification. The review also highlights technical challenges and key hurdles that MXenes currently face in AZIBs.

Working mechanism of MXene as the anode protection layer of aqueous zinc-ion batteries

In recent years, the research on intrinsically safe aqueous zinc-ion batteries (AZIBs) has gained significant attention. However, the commercialization of AZIBs is hindered because of the formation of dendrites in them and undesired hydrogen evolution reaction (HER) at their anode. MXene is a promising two-dimensional material that can inhibit dendrite growth and undesired HER at the anode when used as a protective layer for the anode in AZIBs. MXene's surface functional groups play a crucial role in this protective function. However, the working mechanisms of these surface functional groups have not been thoroughly understood. Based on first-principles calculations and molecular dynamics simulation, we investigated the mechanisms of MXene with nine surface functional groups, including oxygen and halogen elements, as an anode protection layer. We checked their structural stability, electronic structure, adsorption energy, HER reaction free energy, Zn2+ diffusion energy barriers, coordination number of Zn2+- H2O and diffusion coefficients of Zn2+. The MXene species with -S and -O functional groups exhibit good electrical conductivity and greatly adsorb Zn2+. Conversely, MXene species with halogen-functional groups significantly inhibit HER reactions. MXene materials with -Se functional group have the best desolvation effect (ΔCN = 0.31), while those with -I end group have the fastest ability to diffuse zinc ion. This research provides a theoretical guidance for the design of MXene based anode protection layers, which can help to develop dendrite-free and low side-reaction AZIBs.

Advances of Electrochemical and Electrochemiluminescent Sensors Based on Covalent Organic Frameworks

Covalent organic frameworks (COFs), a rapidly developing category of crystalline conjugated organic polymers, possess highly ordered structures, large specific surface areas, stable chemical properties, and tunable pore microenvironments. Since the first report of boroxine/boronate ester-linked COFs in 2005, COFs have rapidly gained popularity, showing important application prospects in various fields, such as sensing, catalysis, separation, and energy storage. Among them, COFs-based electrochemical (EC) sensors with upgraded analytical performance are arousing extensive interest. In this review, therefore, we summarize the basic properties and the general synthesis methods of COFs used in the field of electroanalytical chemistry, with special emphasis on their usages in the fabrication of chemical sensors, ions sensors, immunosensors, and aptasensors. Notably, the emerged COFs in the electrochemiluminescence (ECL) realm are thoroughly covered along with their preliminary applications. Additionally, final conclusions on state-of-the-art COFs are provided in terms of EC and ECL sensors, as well as challenges and prospects for extending and improving the research and applications of COFs in electroanalytical chemistry.

Core-Shell Structure Trimetallic Sulfide@N-Doped Carbon Composites as Anodes for Enhanced Lithium-Ion Storage Performance

The high specific capacity of transition metal sulfides (TMSs) opens up a promising new development direction for lithium-ion batteries with high energy storage. However, the poor conductivity and serious volume expansion during charge and discharge hinder their further development. In this work, trimetallic sulfide Zn-Co-Fe-S@nitrogen-doped carbon (Zn-Co-Fe-S@N-C) polyhedron composite with a core-shell structure is synthesized through a simple self-template method using ZnCoFe-ZIF as precursor, followed by a dopamine surface polymerization process and sulfidation during high-temperature calcination. The obvious space between the internal core and the external shell of the Zn-Co-Fe-S@N-C composites can effectively alleviate the volume expansion and shorten the diffusion path of Li ions during charge and discharge cycles. The nitrogen-doped carbon shell not only significantly improves the electrical conductivity of the material, but also strengthens the structural stability of the material. The synergistic effect between polymetallic sulfides improves the electrochemical reactivity. When used as an anode in lithium-ion batteries (LIBs), the prepared Zn-Co-Fe-S@N-C composite exhibits a high specific capacity retention (966.6 mA h g-1 after 100 cycles at current rate of 100 mA g-1) and good cyclic stability (499.17 mA h g-1 after 120 cycles at current rate of 2000 mA g-1).

Review of Design Routines of MXene Materials for Magnesium-Ion Energy Storage Device

Renewable energy storage using electrochemical storage devices is extensively used in various field applications. High-power density supercapacitors and high-energy density rechargeable batteries are some of the most effective devices, while lithium-ion batteries (LIBs) are the most common. Due to the scarcity of Li resources and serious safety concerns during the construction of LIBs, development of safer and cheaper technologies with high performance is warranted. Magnesium is one of the most abundant and replaceable elements on earth, and it is safe as it does not generate dendrite following cycling. However, the lack of suitable electrode materials remains a critical issue in developing electrochemical energy storage devices. 2D MXenes can be used to construct composites with different dimensions, owing to their suitable physicochemical properties and unique magnesium-ion adsorption structure. In this study, the construction strategies of MXene in different dimensions, including its physicochemical properties as an electrode material in magnesium ion energy storage devices are reviewed. Research advancements of MXene and MXene-based composites in various kinds of magnesium-ion storage devices are also analyzed to understand its energy storage mechanisms. Finally, current opportunities, challenges, and future prospects are also briefly discussed to provide crucial information for future research.

In Situ Anchoring Ultrafine ZnS Nanodots on 2D MXene Nanosheets for Accelerating Polysulfide Redox and Regulating Li Plating

Lithium-sulfur (Li-S) battery is a promising energy storage system due to its cost effectiveness and high energy density. However, formation of Li dendrites from Li metal anode and shuttle effect of lithium polysulfides (LiPSs) from S cathode impede its practical application. Herein, ultrafine ZnS nanodots are uniformly grown on 2D MXene nanosheets by a low-temperature (60 °C) hydrothermal method for the first time. Distinctively, the ZnS nanodot-decorated MXene nanosheets (ZnS/MXene) can be easily filtered to be a flexible and freestanding film in several minutes. The ZnS/MXene film can be used as a current collector for Li-metal anode to promote uniform Li deposition due to the superior lithiophilicity of ZnS nanodots. ZnS/MXene powders obtained by freeze drying can be used as separator decorator to address the shuttle effect of LiPSs due to their excellent adsorbability. Theoretical calculation proves that the existence of ZnS nanodots on MXene can obviously improve the adsorption ability of ZnS/MXene with Li+ and LiPSs. Li-S full cells with composite Li-metal anode and modified separator exhibit remarkable rate and cycling performance. Other transition metal sulfides (CdS, CuS, etc.) can be also grown on 2D MXene nanosheets by the low-temperature hydrothermal strategy.

Progression in the Oxidation Stability of MXenes

MXenes are under the spotlight due to their versatile physicochemical characteristics. Since their discovery in 2011, significant advancements have been achieved in their synthesis and application sectors. However, the spontaneous oxidation of MXenes, which is critical to its processing and product lifespan, has gotten less attention due to its chemical complexity and poorly understood oxidation mechanism. This perspective focuses on the oxidation stability of MXenes and addresses the most recent advancements in understanding and the possible countermeasures to limit the spontaneous oxidation of MXenes. A section is dedicated to the presently accessible methods for monitoring oxidation, with a discussion on the debatable oxidation mechanism and coherently operating factors that contribute to the complexity of MXenes oxidation. The current potential solutions for mitigating MXenes oxidation and the existing challenges are also discussed with prospects to prolong MXene's shelf-life storage and expand their application scope.

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.

Metal-Organic Framework Composites and Their Derivatives as Efficient Electrodes for Energy Storage Applications: Recent Progress and Future Perspectives

Metal-organic frameworks (MOFs) have been important electrochemical energy storage (EES) materials because of their rich species, large specific surface area, high porosity and rich active sites. Nevertheless, the poor conductivity, low mechanical and electrochemical stability of pristine MOFs have hindered their further applications. Although single component MOF derivatives have higher conductivity, self-aggregation often occurs during preparation. Composite design can overcome the shortcomings of MOFs and derivatives and create synergistic effects, resulting in improved electrochemical properties for EES. In this review, recent applications of MOF composites and derivatives as electrodes in different types of batteries and supercapacitors are critically discussed. The advantages, challenges, and future perspectives of MOF composites and derivatives have been given. This review may guide the development of high-performance MOF composites and derivatives in the field of EES.

Single-Phase Ternary Compounds with a Disordered Lattice and Liquid Metal Phase for High-Performance Li-Ion Battery Anodes

Si is considered as the promising anode materials for lithium-ion batteries (LIBs) owing to their high capacities of 4200 mAh g-1 and natural abundancy. However, severe electrode pulverization and poor electronic and Li-ionic conductivities hinder their practical applications. To resolve the afore-mentioned problems, we first demonstrate a cation-mixed disordered lattice and unique Li storage mechanism of single-phase ternary GaSiP2 compound, where the liquid metallic Ga and highly reactive P are incorporated into Si through a ball milling method. As confirmed by experimental and theoretical analyses, the introduced Ga and P enables to achieve the stronger resistance against volume variation and metallic conductivity, respectively, while the cation-mixed lattice provides the faster Li-ionic diffusion capability than those of the parent GaP and Si phases. The resulting GaSiP2 electrodes delivered the high specific capacity of 1615 mAh g-1 and high initial Coulombic efficiency of 91%, while the graphite-modified GaSiP2 (GaSiP2@C) achieved 83% of capacity retention after 900 cycles and high-rate capacity of 800 at 10,000 mA g-1. Furthermore, the LiNi0.8Co0.1Mn0.1O2//GaSiP2@C full cells achieved the high specific capacity of 1049 mAh g-1 after 100 cycles, paving a way for the rational design of high-performance LIB anode materials.

Van der Waals Interaction-Driven Self-Assembly of V2O5 Nanoplates and MXene for High-Performing Zinc-Ion Batteries by Suppressing Vanadium Dissolution

Aqueous zinc-ion batteries (AZIBs) are attractive energy storage devices that benefit from improved safety and negligible environmental impact. The V₂O₅-based cathodes are highly promising, but the dissolution of vanadium is one of the major challenges in realizing their stable performance in AZIBs. Herein, we design a Ti₃C₂T_x MXene layer on the surface of V₂O₅ nanoplates (VPMX) through a van der Waals self-assembly approach for suppressing vanadium dissolution during an electrochemical process for greatly boosting the zinc-ion storage performance. Unlike conventional V₂O₅/C composites, we demonstrate that the VPMX hybrids offer three distinguishable features for achieving high-performance AZIBs: (i) the MXene layer on cathode surface maintains structural integrity and suppresses V dissolution; (ii) the heterointerface between V₂O₅ and MXene enables improved host electrochemical kinetics; (iii) reduced electrostatic repulsion exists among host layers owing to the lubricating water molecules in the VPMX cathode, facilitating interfacial Zn²⁺ diffusion. As a result, the as-made VPMX cathode shows a long-term cycling stability over 5000 cycles, surpassing other reported V₂O₅-based materials. Especially, we find that the heterointerface between V₂O₅ and MXene and lubricated water molecules in the host can achieve an enhanced rate capability (243.6 mAh g^-1 at 5.0 A g^-1) for AZIBs.

Metal-Organic Framework Materials for Electrochemical Supercapacitors

Exploring new materials with high stability and capacity is full of challenges in sustainable energy conversion and storage systems. Metal-organic frameworks (MOFs), as a new type of porous material, show the advantages of large specific surface area, high porosity, low density, and adjustable pore size, exhibiting a broad application prospect in the field of electrocatalytic reactions, batteries, particularly in the field of supercapacitors. This comprehensive review outlines the recent progress in synthetic methods and electrochemical performances of MOF materials, as well as their applications in supercapacitors. Additionally, the superiorities of MOFs-related materials are highlighted, while major challenges or opportunities for future research on them for electrochemical supercapacitors have been discussed and displayed, along with extensive experimental experiences.

MXene based nanocomposite films

Since the first report in 2011, two-dimensional transition metal carbide/nitride MXenes have aroused widespread attention owing to the particular structure and physiochemical properties. In the last few years, MXene-based nanocomposite films have been widely investigated, showing promising applications in many fields. However, poor mechanical properties and thermal/electrical conductivities of MXene-based nanocomposite films still limited their practical applications. Herein, we summarize the fabrication approach of MXene-based nanocomposite films and discuss the mechanical properties and other applications, including electromagnetic interference shielding, thermal conductivity, and supercapacitors. Then, several vital factors for fabricating high performance MXene based nanocomposite films have been refined. To further fabricate high performance MXene-based nanocomposite films, some effective sequential bridging strategies are also discussed. Lastly, a conclusion of the challenges and opportunities of MXene-based nanocomposite films is provided to facilitate their development and application for various purposes in the future of scientific research.

Advances of MXenes; Perspectives on Biomedical Research

The last decade witnessed the emergence of a new family of 2D transition metal carbides and nitrides named MXenes, which quickly gained momentum due to their exceptional electrical, mechanical, optical, and tunable functionalities. These outstanding properties also rendered them attractive materials for biomedical and biosensing applications, including drug delivery systems, antimicrobial applications, tissue engineering, sensor probes, auxiliary agents for photothermal therapy and hyperthermia applications, etc. The hydrophilic nature of MXenes with rich surface functional groups is advantageous for biomedical applications over hydrophobic nanoparticles that may require complicated surface modifications. As an emerging 2D material with numerous phases and endless possible combinations with other 2D materials, 1D materials, nanoparticles, macromolecules, polymers, etc., MXenes opened a vast terra incognita for diverse biomedical applications. Recently, MXene research picked up the pace and resulted in a flood of literature reports with significant advancements in the biomedical field. In this context, this review will discuss the recent advancements, design principles, and working mechanisms of some interesting MXene-based biomedical applications. It also includes major progress, as well as key challenges of various types of MXenes and functional MXenes in conjugation with drug molecules, metallic nanoparticles, polymeric substrates, and other macromolecules. Finally, the future possibilities and challenges of this magnificent material are discussed in detail.

Next-Generation Intelligent MXene-Based Electrochemical Aptasensors for Point-of-Care Cancer Diagnostics

Delayed diagnosis of cancer using conventional diagnostic modalities needs to be addressed to reduce the mortality rate of cancer. Recently, 2D nanomaterial-enabled advanced biosensors have shown potential towards the early diagnosis of cancer. The high surface area, surface functional groups availability, and excellent electrical conductivity of MXene make it the 2D material of choice for the fabrication of advanced electrochemical biosensors for disease diagnostics. MXene-enabled electrochemical aptasensors have shown great promise for the detection of cancer biomarkers with a femtomolar limit of detection. Additionally, the stability, ease of synthesis, good reproducibility, and high specificity offered by MXene-enabled aptasensors hold promise to be the mainstream diagnostic approach. In this review, the design and fabrication of MXene-based electrochemical aptasensors for the detection of cancer biomarkers have been discussed. Besides, various synthetic processes and useful properties of MXenes which can be tuned and optimized easily and efficiently to fabricate sensitive biosensors have been elucidated. Further, futuristic sensing applications along with challenges will be deliberated herein.

Thermal treatment for promoting interfacial interaction in Co-BDC/Ti3C2Tx hybrid nanosheets for hybrid supercapacitors

The design and synthesis of high-performance metal-organic frameworks (MOFs)-based electrodes are important for hybrid supercapacitors (HSC). Herein, enhanced interfacial interaction in Co-BDC/Ti₃C₂T_x (denoted as CoTC) hybrid nanosheets is achieved through thermal treatment, giving remarkably improved capacity performance compared with CoTC. The low temperature annealing treatment enables modulation of the bridging bonds content of CoTC and thus regulates the interfacial coupling effect between Co-BDC and Ti₃C₂T_x. Moreover, both the detailed XPS and XANES analysis reveal that the strong interfacial interactions between the two components promote a partial electron transfer from Ti₃C₂T_x to Co-BDC through the Ti-O-Co interfacial bonds. Consequently, it endows the Co-BDC with enhanced conductivity as well as the higher valence of Ti species in Ti₃C₂T_x, hence contributes a remarkable enhanced specific capacity. This work will provide a pathway to design advanced MOF/MXene materials for HSC.

Defect-Selectivity and "Order-in-Disorder" Engineering in Carbon for Durable and Fast Potassium Storage

Defect-rich carbon materials possess high gravimetric potassium storage capability due to the abundance of active sites, but their cyclic stability is limited because of the low reversibility of undesirable defects and the deteriorative conductivity. Herein, in situ defect-selectivity and order-in-disorder synergetic engineering in carbon via a self-template strategy is reported to boost the K⁺ -storage capacity, rate capability and cyclic stability simultaneously. The defect-sites are selectively tuned to realize abundant reversible carbon-vacancies with the sacrifice of poorly reversible heteroatom-defects through the persistent gas release during pyrolysis. Meanwhile, nanobubbles generated during the pyrolysis serve as self-templates to induce the surface atom rearrangement, thus in situ embedding nanographitic networks in the defective domains without serious phase separation, which greatly enhances the intrinsic conductivity. The synergetic structure ensures high concentration of reversible carbon-vacancies and fast charge-transfer kinetics simultaneously, leading to high reversible capacity (425 mAh g^-1 at 0.05 A g^-1 ), high-rate (237.4 mAh g^-1 at 1 A g^-1 ), and superior cyclic stability (90.4% capacity retention from cycle 10 to 400 at 0.1 A g^-1 ). This work provides a rational and facile strategy to realize the tradeoff between defect-sites and intrinsic conductivity, and gives deep insights into the mechanism of reversible potassium storage.