MXene/Graphene Heterostructures as High-Performance Electrodes for Li-Ion Batteries

BlueP encapsulated Janus MoSSe as a promising heterostructure anode material for LIBs

In this work, the significance of BlueP-Janus MoSSe heterostructures in LIBs is explored in detail by using density functional theory calculations. The Janus MoSSe possesses two different atomic layers, and hence two different heterostructures, BlueP-SMoSe and BlueP-SeMoS, are taken into account. The heterostructure formation energies are computed to check their stability. Besides, ab initio molecular dynamics simulations and phonon studies are done to check their thermal and dynamical stabilities, respectively. The adsorption and diffusion of Li at different surfaces of both the heterostructures are calculated. Our study reveals that the heterostructures show strong Li intercalation capability with ultrafast Li diffusion barrier energies. The electronic properties of the lithiated heterointerfaces are also explored. Both the heterostructures can hold a maximum of two layers of Li ions on each side of both BlueP and MoSSe to give a large storage capacity, signifying their extraordinary potential to be appropriate as an anode material for Li-ion batteries. Additionally, due to their strong mechanical strength, the 2D BlueP-Janus MoSSe heterostructures can withstand massive volume expansion during the lithiation-delithiation reaction, which is remarkably beneficial for manufacturing flexible anodes. Based on the above findings, the newly designed heterostructures are expected to open a new avenue for the next generation of electronic devices.

Interfacial Design of Ti3C2Tx MXene/Graphene Heterostructures Boosted Ru Nanoclusters with High Activity Toward Hydrogen Evolution Reaction

The development of a cost-competitive and efficient electrocatalyst is both attractive and challenging for hydrogen production by hydrogen evolution reaction (HER). Herein, a facile glycol reduction method to construct Ru nanoclusters coupled with hierarchical exfoliated-MXene/reduced graphene oxide architectures (Ru-E-MXene/rGA) is reported. The hierarchical structure, formed by the self-assembly of graphene oxides, can effectively prohibit the self-stacking of MXene nanosheets. Meanwhile, the formation of the MXene/rGA interface can strongly trap the Ru3+ ions, resulting in the uniform distribution of Ru nanoclusters within Ru-E-MXene/rGA. The boosted catalytic activity and underlying catalytic mechanism during the HER process are proved by density functional theory. Ru-E-MXene/rGA exhibits overpotentials of 42 and 62 mV at 10 mA cm-2 in alkaline and acidic electrolytes, respectively. The small Tafel slope and charge transfer resistance (Rct) values elucidate its fast dynamic behavior. The cyclic voltammetry (CV) curves and chronoamperometry test confirm the high stability of Ru-E-MXene/rGA. These results demonstrate that coupling Ru nanoclusters with the MXene/rGA heterostructure represents an efficient strategy for constructing MXene-based catalysts with enhanced HER activity.

Molecularly Imprinted Polymer Biosensor Based on Nitrogen-Doped Electrochemically Exfoliated Graphene/Ti3 CNTX MXene Nanocomposite for Metabolites Detection

Rapid and accurate quantification of metabolites in different bodily fluids is crucial for a precise health evaluation. However, conventional metabolite sensing methods, confined to centralized laboratory settings, suffer from time-consuming processes, complex procedures, and costly instrumentation. Introducing the MXene/nitrogen-doped electrochemically exfoliated graphene (MXene@N-EEG) nanocomposite as a novel biosensing platform in this work addresses the challenges associated with conventional methods, leveraging the concept of molecularly imprinted polymers (MIP) enables the highly sensitive, specific, and reliable detection of metabolites. To validate our biosensing technology, we utilize agmatine as a significant biologically active metabolite. The MIP biosensor incorporates electrodeposited Prussian blue nanoparticles as a redox probe, facilitating the direct electrical signaling of agmatine binding in the polymeric matrix. The MXene@N-EEG nanocomposite, with excellent metal conductivity and a large electroactive specific surface area, effectively stabilizes the electrodeposited Prussian blue nanoparticles. Furthermore, increasing the content of agmatine-imprinted cavities on the electrode enhances the sensitivity of the MIP biosensor. Evaluation of the designed MIP biosensor in buffer solution and plasma samples reveals a wide linear concentration range of 1.0 nM-100.0 μM (R2 = 0.9934) and a detection limit of 0.1 nM. Notably, the developed microfluidic biosensor offers low cost, rapid response time to the target molecule (10 min of sample incubation), good recovery results for detecting agmatine in plasma samples, and acceptable autonomous performance for on-chip detection. Moreover, its high reliability and sensitivity position this MIP-based biosensor as a promising candidate for miniaturized microfluidic devices with the potential for scalable production for point-of-care applications.

MXene-Based Chemo-Sensors and Other Sensing Devices

MXenes have received worldwide attention across various scientific and technological fields since the first report of the synthesis of Ti3C2 nanostructures in 2011. The unique characteristics of MXenes, such as superior mechanical strength and flexibility, liquid-phase processability, tunable surface functionality, high electrical conductivity, and the ability to customize their properties, have led to the widespread development and exploration of their applications in energy storage, electronics, biomedicine, catalysis, and environmental technologies. The significant growth in publications related to MXenes over the past decade highlights the extensive research interest in this material. One area that has a great potential for improvement through the integration of MXenes is sensor design. Strain sensors, temperature sensors, pressure sensors, biosensors (both optical and electrochemical), gas sensors, and environmental pollution sensors targeted at volatile organic compounds (VOCs) could all gain numerous improvements from the inclusion of MXenes. This report delves into the current research landscape, exploring the advancements in MXene-based chemo-sensor technologies and examining potential future applications across diverse sensor types.

Properties of Layered TMDC Superlattices for Electrodes in Li-Ion and Mg-Ion Batteries

In this work, we present a first-principles investigation of the properties of superlattices made from transition metal dichalcogenides for use as electrodes in lithium-ion and magnesium-ion batteries. From a study of 50 pairings, we show that, in general, the volumetric expansion, intercalation voltages, and thermodynamic stability of vdW superlattice structures can be well approximated with the average value of the equivalent property for the component layers. We also found that the band gap can be reduced, improving the conductivity. Thus, we conclude that superlattice construction can be used to improve material properties through the tuning of intercalation voltages toward specific values and by increasing the stability of conversion-susceptible materials. For example, we demonstrate how pairing SnS2 with systems such as MoS2 can change it from a conversion to an intercalation material, thus opening it up for use in intercalation electrodes.

Manipulation of electrochemical properties of MXene electrodes for supercapacitor applications by chemical and magnetic disorder

The potential of two-dimensional MXenes as electrodes in supercapacitor applications has been studied extensively. However, the role of chemical and magnetic disorder in their electrochemical parameters, e.g., capacitance, has not been explored yet. In this work, we have systematically addressed this for V2-xMnxCO2 MXene solid solutions with an analysis based upon the results from first-principles electronic structure calculations. We find that the variations in the total capacitance over a voltage window depend on the degree of chemical and magnetic disorder. In the course of our investigation, it was also found that the magnetic structure on the surface can substantially influence the redox charge transfer, an as yet unexplored phenomenon. A significantly large charge transfer and thus a large capacitance can be obtained by manipulating the chemical composition and the magnetic order of the surfaces. These findings can be useful in designing operational supercapacitor electrodes with magnetic constituents.

Black phosphorene/SnSe van der Waals heterostructure as a promising anchoring anode material for metal-ion batteries

Black phosphorene (BP) is a glowing two-dimensional semiconducting layer material for cutting-edge microelectronics, with high carrier mobility and thickness-dependent band gap. Here, based on van der Waals (vdW)-corrected first-principles approaches, we investigated stacked BP/tin selenide (BP/SnSe) vdW heterostructure as an anode material for metal ion batteries, which exhibits a significant theoretical capacity, along with relatively durable binding strength compared to the constituent BP and SnSe monolayers. Our calculations demonstrated that the Li/Na adatom favors insertion into the interlayer region of BP/SnSe vdW heterostructure owing to synergistic interfacial effect, resulting in comparable diffusivity to the BP and SnSe monolayers. Subsequently, the theoretical specific capacities for Li/Na are found to be as high as 956.30 mAhg-1and 828.79 mAhg-1, respectively, which could be attributed to the much higher storage capacity of Li/Na adatoms in the BP/SnSe vdW heterostructure. Moreover, the electronic structure calculations reveal that a large amount of charge transfer assists in semiconductor-to-metallic transition upon lithiation/sodiation, ensuring good electrical conductivity. These simulations verify that the BP/SnSe vdW heterostructure has immense potential for application in the design of metal-ion battery technologies.

Interlayer electronic coupling regulates the performance of FeN MXenes and Fe2B2 MBenes as high-performance Li- and Al-ion batteries

When two-dimensional (2D) materials are stacked into van der Waals structures, interlayer electronic coupling can induce excellent properties in energy storage materials. Here, we investigate the interlayer coupling of the FeN/Fe2B2 heterojunction as an anode material, which is constructed using vertically planar FeN and puckered Fe2B2 nanosheets. These structures were searched by the CALYPSO method and computed by density functional theory calculations. The stabilities of the FeN monolayer, Fe2B2 monolayer, and FeN/Fe2B2 heterojunction were tested in terms of dynamics, mechanics, and thermodynamics, respectively. These structures have good performances as anode materials, including the capacities of the FeN (Fe2B2) monolayer of 9207 mA h g-1 (2713 mA h g-1) and 3069 mA h g-1 (1005 mA h g-1) for Al and Li, respectively. The stable FeN/Fe2B2 heterojunction shows extremely low diffusion barriers of 0.01 eV, a high Al ion capacity of 4254 mA h g-1, and relatively low voltages. Hess's law revealed that the interlayer electronic coupling impacts the adsorption process of the FeN layer in the FeN/Fe2B2 heterojunction, which decreases the pz orbital of the N atom for the heterojunction. The unequal distribution of electrons between the layers results in interlayer polarization; the value of interlayer polarization was quantitatively calculated to be 0.64 pC m-1. The presence of adsorbed Li and Al atoms between the layers helps maintain the original structure and prevents the interlayer sliding from damaging the heterojunction. These findings offer insights for understanding the structural and electronic properties of the FeN/Fe2B2 heterojunction, which provides crucial information for rational design and advanced synthesis of novel electrode materials.

Pillaring Behavior of Organic Molecules on MXene: Insights from Molecular Dynamics Simulations

Pillaring MXene with organic molecules is an effective approach to expand the interlayer spacing and increase the accessible surface area for enhanced performance in energy storage applications. Herein, molecular dynamics simulations are employed to explore the pillaring effect of six organic molecules on Ti3C2O2. The interlayer spacing and structural characteristics of MXene after the insertion of different organic molecules are examined, and the influence of the type and quantity of organic molecules on the pillared MXene structure is systematically investigated. The results demonstrate that the inserted molecules are influenced by interactions between MXene layers, resulting in a thinner morphology. Effective pillar support on MXene is achieved only when a specific quantity of organic molecules is inserted between the layers. Furthermore, different organic molecules occupy distinct surface areas on MXene when acting as pillars. Pillaring molecules with a Pi-conjugated ring structure require a larger surface area on MXene, whereas those with a branched structure occupy a smaller surface area. Additionally, organic molecules containing oxygen functional groups tend to aggregate due to hydrogen bonding, impeding their diffusion within MXene sheets. Considering the interlayer expansion of MXene, surface area occupation, and diffusion characteristics, the isopropylamine demonstrates the most favorable pillaring effect on MXene. These findings provide valuable insights into the design and application of pillared MXenes in energy storage and other applications. Further studies on the properties and applications of the optimized pillared MXene structures will be conducted in the future.

Graphene Film with a Controllable Microstructure for Efficient Electrochemical Energy Storage

The agglomeration of graphene sheets and undesired pore size distribution usually lead to unsatisfactory electrochemical properties of reduced graphene oxide (RGO) film electrodes. Herein, crumpled exfoliated graphene (EG) sheets are adopted as the microstructure-regulating agent to tune the morphology and micro-/mesopore amounts with the aim of increasing active surface sites and ion transportation paths in electrodes. With the optimum ratio between EG and GO, the resulting 75%-EG/RGO shows significantly improved specific gravimetric capacitance (C_s) and rate capability when compared with pure RGO electrodes in a symmetrical supercapacitor system. Moreover, when coupling the 75%-EG/RGO cathode with a Zn anode to form a Zn ion hybrid supercapacitor (ZHS), the 75%-EG/RGO exhibits a much higher C_s of 327.39 F g^-1 at 0.1 A g^-1 and can maintain 91.7% capacitance after 8000 cycles. Systematic ex situ X-ray diffraction (XRD) and X-ray photoelectron spectra (XPS) measurements reveal that the charge storage mechanism is based on both reversible physical adsorption and dual ion uptake. Furthermore, the quasi-solid-state flexible ZHS also presents high capacitive performance and can maintain ∼100% capacitance under various bending states, demonstrating potential application in wearable electronics. This strategy opens up a new path for constructing high-performance graphene film electrodes.

Niche Applications of MXene Materials in Photothermal Catalysis

MXene materials have found emerging applications as catalysts for chemical reactions due to their intriguing physical and chemical applications. In particular, their broad light response and strong photothermal conversion capabilities are likely to render MXenes promising candidates for photothermal catalysis, which is drawing increasing attention in both academic research and industrial applications. MXenes are likely to satisfy all three criteria of a desirable photothermal catalyst: strong light absorption, effective heat management, and versatile surface reactivity. However, their specific functionalities are largely dependent on their structure and composition, which makes understandings of the structure–function relationship of crucial significance. In this review, we mainly focus on the recent progress of MXene–based photothermal catalysts, emphasizing the functionalities and potential applications of MXene materials in fields of photothermal catalysis, and provide insights on design principles of highly efficient MXene–based photothermal catalysts from the atomic scale. This review provides a relatively thorough understanding of MXene–based materials for photothermal catalysis, as well as an in–depth investigation of emerging high-prospect applications in photothermal catalysis.

Interfacial effects on lithium-ion diffusion in two-dimensional lateral black phosphorus-graphene heterostructures

Lateral heterostructures constructed from different two-dimensional (2D) materials can be potentially used in lithium-ion batteries (LIBs). The interface between two different components strongly affects LIB charge and discharge processes. Herein, the atomic structures, electronic properties, and Li-ion diffusion characteristics of lateral black phosphorus-graphene (BP-G) heterostructures are studied via first-principles calculations. The obtained results reveal that BP-G heterostructures with either zigzag (ZZ) or misoriented interfaces constructed according to Clar's rule possess a small number of interfacial states and are electronically stable. Furthermore, compared with the perfect ZZ interface of BP-G, Clar's interfaces provide a larger number of diffusion paths with much lower energy barriers. The findings of this study suggest that lateral BP-G heterostructures can provide insights for rapid charge and discharge processes in LIBs.

A High Performance Triboelectric Nanogenerator Based on MXene/Graphene Oxide Electrode for Glucose Detection

A smart sensing platform based on a triboelectric nanogenerator (TENG) possesses various advantages such as self-powering, convenience, real-time and biocompatibility. However, the detection limit of the TENG-based sensor is required to be improved. In this study, a high performance TENG-based glucose sensor was proposed by using the Ti₃C₂T_x (MXene)/graphene oxide (GO) composite electrode. The MXene and GO nanosheets are popular 2D materials which possessed high conductivity and a rich surface functional group. The MXene/GO thin films were prepared through electrostatic self-assembly technology, which can effectively impede the agglomeration of two nanoflakes. The as-prepared MXene/GO film presented outstanding mechanical property. To figure out the relationship between the nanostructure of MXene/GO film and the TENG, a series of MXene/GO-based TENG with different GO sizes was characterized. As a result, the TENG with 400 nm GO demonstrated the highest output performance. Subsequently, the optimized TENG was used in glucose detection application without the assistance of a glucose enzyme. This simple and flexible TENG shows promising potential in biosensors and non-invasive health monitoring.

Metal Ion-Induced Porous MXene for All-Solid-State Flexible Supercapacitors

MXenes are normally used for energy storage applications. However, large nanosheets and restacking are detrimental to the ion diffusion and thus limit its rate capability. Here, a strategy to prepare flexible and porous MXene-M supercapacitor electrodes can simultaneously enlarge the interlayer spacing between layers and create holes in the layers. As a result, Ti₃C₂T_x-Mn presents an excellent lifespan, with still 248 F g^-1 after 100 000 cycles at a current density of 100 A g^-1. Moreover, Ti₃C₂T_x-Mn-based symmetric all-solid-state supercapacitor exhibits outstanding volumetric energy up to 52.4 mWh cm^-3 and retains 38.4 mWh cm^-3 at an ultrahigh volumetric power density of 55.3 W cm^-3. We believe this work provides an idea for the later regulation of MXene layer spacing and the design of porous structures, and can be widely used in the next-generation high-energy density and power density practical applications.

Role of Nanomaterials in the Fabrication of bioNEMS/MEMS for Biomedical Applications and towards Pioneering Food Waste Utilisation

bioNEMS/MEMS has emerged as an innovative technology for the miniaturisation of biomedical devices with high precision and rapid processing since its first R&D breakthrough in the 1980s. To date, several organic including food waste derived nanomaterials and inorganic nanomaterials (e.g., carbon nanotubes, graphene, silica, gold, and magnetic nanoparticles) have steered the development of high-throughput and sensitive bioNEMS/MEMS-based biosensors, actuator systems, drug delivery systems and implantable/wearable sensors with desirable biomedical properties. Turning food waste into valuable nanomaterials is potential groundbreaking research in this growing field of bioMEMS/NEMS. This review aspires to communicate recent progress in organic and inorganic nanomaterials based bioNEMS/MEMS for biomedical applications, comprehensively discussing nanomaterials criteria and their prospects as ideal tools for biomedical devices. We discuss clinical applications for diagnostic, monitoring, and therapeutic applications as well as the technological potential for cell manipulation (i.e., sorting, separation, and patterning technology). In addition, current in vitro and in vivo assessments of promising nanomaterials-based biomedical devices will be discussed in this review. Finally, this review also looked at the most recent state-of-the-art knowledge on Internet of Things (IoT) applications such as nanosensors, nanoantennas, nanoprocessors, and nanobattery.

Tuning the structural stability and electrochemical properties in graphene anode materials by B doping: a first-principles study

The first-principles method of density functional theory (DFT) is used to study the structural stability and electrochemical properties of B doped graphene with concentrations of 3.125%, 6.25% and 18.75% respectively, and their lithium storage mechanism and characteristics are further studied. The results show that the doped systems all have negative adsorption energy, indicating that the structures can exist stably, and the adsorption energy of lithium ions on graphene decreases with the increase of B doping concentration. Among them, the B₆C₂₆ structure has the lowest adsorption energy and can adsorb more lithium ions. The density of states indicates that doping with B can increase the conductivity of graphene greatly. Subsequently, the CI-NEB method to search for the transition state of the doped structure is used, showing that the B₆C₂₆ structure has the lowest diffusion barrier and good rate performance. Therefore, these findings provide a certain research foundation for the development and application of lithium-ion battery anode materials.

Constructing robust polymer/two-dimensional Ti3C2TX solid-state electrolyte interphase via in-situ polymerization for high-capacity long-life and dendrite-free lithium metal anodes

We constructed an artificial polymer/two-dimensional Ti₃C₂T_X (MXene) solid electrolyte interphase (SEI) on a Li metal surface via an in-situ polymerization strategy. The polymer layer provides excellent interface contact and outstanding adaptability for the volume expansion of Li metal, decreasing interface impedance. On the other hand, the two-dimensional MXene with a low Li nucleation energy barrier is beneficial for uniform Li deposition and restraint of interfacial side reactions. In this work, a dense and durable MXene-integrated SEI between the Li metal anode and solid-state electrolyte (SSE) interface is constructed to render the Li/SSE/Li cell to maintain a stable polarization voltage of approximately 50 mV at a capacity of 0.50 mAh cm^-2 for over 1000 h. It enables the Li/SSE/LiFePO₄ cell to deliver a capacity of 130.1 mAh g^-1 at 1C with a capacity retention of 91.4% after 900 cycles. Therefore, we believe that this facile in-situ polymerization method for constructing a layer of polymer/MXene SEI at the interface between Li metal anodes and SSE can promote the practical applications of Li metal batteries.

Hybrid MXene-Graphene/Hexagonal Boron Nitride Structures: Electronic and Molecular Adsorption Properties

Recent advances in experimental techniques allow for the fabrication of hybrid structures. Here, we study the electronic and molecular adsorption properties of the graphene (G)/hexagonal boron nitride (h-BN)-MXenes (Mo2C) hybrid nanosheets. We use first-principles calculations to explore the structure and electronic properties of the hybrid structures of G-2H-Mo2C and h-BN-2H-Mo2C with two different oxygen terminations of the Mo2C surface. The embedding of G or h-BN patches creates structural defects at the patch-Mo2C border and adds new states in the vicinity of the Fermi energy. Since this can be utilized for molecular adsorption and/or sensing, we investigate the ability of the G-M-O1 and BN-M-O1 hybrid structures to adsorb twelve molecules. Generally, the adsorption on the hybrid systems is significantly higher than on the pristine systems, except for N2 and H2, which are weakly adsorbed on all systems. We find that OH, NO, NO2, and SO2 are chemisorbed on the hybrid systems. COOH may be chemisorbed, or it may dissociate depending on its location at the edge between the G/h-BN and the MXene. NH3 is chemisorbed/physisorbed on the BN/G-M-O1 systems. CO, H2S, CO2, and CH4 are physisorbed on the hybrid systems. Our results indicate that the studied hybrid systems can be used for molecular filtration/sensing and catalysis.

Black phosphorene/NP heterostructure as a novel anode material for Li/Na-ion batteries

Designing heterostructured anode materials has been rendered supremely appealing to large-scale energy storage systems and storage device researchers. Recently, black phosphorene has experienced explosive development and been sought for widespread application in various domains including anode materials for electrochemistry. Hence, in this work, the black phosphorene/NP heterostructure (black P/NP) as a novel anode material for Li/Na batteries was systematically studied on the basis of first-principle calculations. Our simulations disclose that black P/NP is dynamically stable at room temperature and exhibits metallic properties. Charge density difference calculations and work function analysis demonstrate that electron charge transfer between the pristine single-layer components leads to enhanced Li/Na ion adsorption on the interlayer. To be specific, the calculated adsorption energies for Li/Na are -2.27 and -2.13 eV, respectively, which are sufficient to prevent metal aggregation during cycling. Besides, it is predicated that black P/NP has a positive and low open-circuit voltage. Excitingly, the diffusion barriers for Li and Na ions on black P/NP are 0.17 and 0.04 eV, respectively, which are superior to other typical heterostructures. Our results may be a new paradigm and reference for phosphorene-based heterostructures used as electrode materials of metal-ion batteries.

MXene-Graphene Composites: A Perspective on Biomedical Potentials

MXenes, transition metal carbides and nitrides with graphene-like structures, have received considerable attention since their first discovery. On the other hand, Graphene has been extensively used in biomedical and medicinal applications. MXene and graphene, both as promising candidates of two-dimensional materials, have shown to possess high potential in future biomedical applications due to their unique physicochemical properties such as superior electrical conductivity, high biocompatibility, large surface area, optical and magnetic features, and extraordinary thermal and mechanical properties. These special structural, functional, and biological characteristics suggest that the hybrid/composite structure of MXene and graphene would be able to meet many unmet needs in different fields; particularly in medicine and biomedical engineering, where high-performance mechanical, electrical, thermal, magnetic, and optical requirements are necessary. However, the hybridization and surface functionalization should be further explored to obtain biocompatible composites/platforms with unique physicochemical properties, high stability, and multifunctionality. In addition, toxicological and long-term biosafety assessments and clinical translation evaluations should be given high priority in research. Although very limited studies have revealed the excellent potentials of MXene/graphene in biomedicine, the next steps should be toward the extensive research and detailed analysis in optimizing the properties and improving their functionality with a clinical and industrial outlook. Herein, different synthesis/fabrication methods and performances of MXene/graphene composites are discussed for potential biomedical applications. The potential toxicological effects of these composites on human cells and tissues are also covered, and future perspectives toward more successful translational applications are presented. The current state-of-the-art biotechnological advances in the use of MXene-Graphene composites, as well as their developmental challenges and future prospects are also deliberated. Due to the superior properties and multifunctionality of MXene-graphene composites, these hybrid structures can open up considerable new horizons in future of healthcare and medicine.

Functional Group Regulated Ni/Ti3C2Tx (Tx = F, -OH) Holding Bimolecular Activation Tunnel for Enhanced Ammonia Borane Hydrolysis

Developing economical and efficient catalyst for hydrogen generation from ammonia borane (AB) hydrolysis is still a huge challenge. As an alternative strategy, the functional group regulation of metal nanoparticles (NPs)-based catalysts is believed to be capable of improving the catalytic activity. Herein, a series of Ni/Ti₃C₂T_x-Y (T_x = F, -OH; Y denotes etching time (d)) catalysts are synthesized and show remarkably enhanced catalytic activity on the hydrolysis of AB in contrast to the corresponding without regulating. The optimized Ni/Ti₃C₂T_x-4 with a turnover frequency (TOF) value of 161.0 min^-1 exhibits the highest catalytic activity among the non-noble monometallic-based catalyst. Experimental results and theory calculations demonstrate that the excellent catalytic activity benefits from the bimolecular activation channels formed by Ni NPs and Ti₃C₂T_x-Y. H₂O and AB molecules are activated simultaneously in the bimolecular activation tunnel. Bimolecular activation reduces the activation energy of AB hydrolysis, and hydrogen generation rate is promoted. This article provides a new approach to design effective catalysts and further supports the bimolecular activation model for the hydrolysis of AB.

Theoretical Design and Structural Modulation of a Surface-Functionalized Ti3C2Tx MXene-Based Heterojunction Electrocatalyst for a Li-Oxygen Battery

Two-dimensional MXene with high conductivity has metastable Ti atoms and inert functional groups on the surface, greatly limiting application in surface-related electrocatalytic reactions. A surface-functionalized nitrogen-doped two-dimensional TiO₂/Ti₃C₂T_x heterojunction (N-TiO₂/Ti₃C₂T_x) was fabricated theoretically, with high conductivity and optimized electrocatalytic active sites. Based on the conductive substrate of Ti₃C₂T_x, the heterojunction remained metallic and efficiently accelerated the transfer of Li⁺ and electrons in the electrode. More importantly, the precise regulation of active sites in the N-TiO₂/Ti₃C₂T_x heterojunction optimized the adsorption for LiO₂ and Li₂O₂, facilitating the sluggish kinetics with a lowest theoretical overpotential in both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Employed as an electrocatalyst in a Li-oxygen battery (Li-O₂ battery), it demonstrated a high specific capacity of 15 298 mAh g^-1 and a superior cyclability with more than 200 cycles at 500 mA g^-1, as well as the swiftly reduced overpotential. Furthermore, combined with the in situ differential electrochemical mass spectrometry, ex situ Raman spectra, and SEM tests, the N-TiO₂/Ti₃C₂T_x heterojunction electrode presented a superior stability and reduced side reaction along with the high performance toward the ORR and OER. It provides an efficient insight for the design of high-performance electrocatalysts for metal-oxygen batteries.

High-Efficiency Electromagnetic Interference Shielding of rGO@FeNi/Epoxy Composites with Regular Honeycomb Structures

With the rapid development of fifth-generation mobile communication technology and wearable electronic devices, electromagnetic interference and radiation pollution caused by electromagnetic waves have attracted worldwide attention. Therefore, the design and development of highly efficient EMI shielding materials are of great importance. In this work, the three-dimensional graphene oxide (GO) with regular honeycomb structure (GH) is firstly constructed by sacrificial template and freeze-drying methods. Then, the amino functionalized FeNi alloy particles (f-FeNi) are loaded on the GH skeleton followed by in-situ reduction to prepare rGH@FeNi aerogel. Finally, the rGH@FeNi/epoxy EMI shielding composites with regular honeycomb structure is obtained by vacuum-assisted impregnation of epoxy resin. Benefitting from the construction of regular honeycomb structure and electromagnetic synergistic effect, the rGH@FeNi/epoxy composites with a low rGH@FeNi mass fraction of 2.1 wt% (rGH and f-FeNi are 1.2 and 0.9 wt%, respectively) exhibit a high EMI shielding effectiveness (EMI SE) of 46 dB, which is 5.8 times of that (8 dB) for rGO/FeNi/epoxy composites with the same rGO/FeNi mass fraction. At the same time, the rGH@FeNi/epoxy composites also possess excellent thermal stability (heat-resistance index and temperature at the maximum decomposition rate are 179.1 and 389.0 °C respectively) and mechanical properties (storage modulus is 8296.2 MPa).

The interlayer coupling modulation of a g-C3N4/WTe2 heterostructure for solar cell applications

Constructing van der Waals (vdW) heterostructures has been proved to be an excellent strategy to design or modulate the physical and chemical properties of 2D materials. Here, we investigated the electronic structures and solar cell performances of the g-C₃N₄/WTe₂ heterostructure via first-principles calculations. It is highlighted that the g-C₃N₄/WTe₂ heterostructure presents a type-II band edge alignment with a band gap of 1.24 eV and a corresponding visible light absorption coefficient of ∼10⁶ cm⁻¹ scale. Interestingly, the band gap of the g-C₃N₄/WTe₂ heterostructure could increase to 1.44 eV by enlarging the vdW gap to harvest more visible light energy. It is worth noting that the decreased band alignment difference resulting from tuning the vdW gap, leads to a promotion of the power conversion efficiency up to 17.68%. This work may provide theoretical insights into g-C₃N₄/WTe₂ heterostructure-based next-generation solar cells, as well as a guide for tuning properties of vdW heterostructures.

g-C₃N₄/WTe₂ heterostructure with tunable vdW gap shows a favorable solar energy conversion performance.

Proton dynamics in water confined at the interface of the graphene-MXene heterostructure

Heterostructures of 2D materials offer a fertile ground to study ion transport and charge storage. Here, we use ab initio molecular dynamics to examine the proton-transfer/diffusion and redox behavior in a water layer confined in the graphene-Ti₃C₂O₂ heterostructure. We find that in comparison with the similar interface of water confined between Ti₃C₂O₂ layers, the proton redox rate in the dissimilar interface of graphene-Ti₃C₂O₂ is much higher, owing to the very different interfacial structure as well as the interfacial electric field induced by an electron transfer in the latter. Water molecules in the dissimilar interface of the graphene-Ti₃C₂O₂ heterostructure form a denser hydrogen-bond network with a preferred orientation of water molecules, leading to an increase in proton mobility with proton concentration in the graphene-Ti₃C₂O₂ interface. As the proton concentration further increases, proton mobility decreases due to increasingly more frequent surface redox events that slow down proton mobility due to binding with surface O atoms. Our work provides important insights into how the dissimilar interface and their associated interfacial structure and properties impact proton transfer and redox in the confined space.

Temperature-Invariant Superelastic Multifunctional MXene Aerogels for High-Performance Photoresponsive Supercapacitors and Wearable Strain Sensors

Assembling MXene two-dimensional (2D) nanosheets solely into structurally robust three-dimensional (3D) multifunctional macroarchitectures with temperature-invariant elasticity is significant for widening their potential applications but has remained exceedingly challenging. To this end, a facile freeze-induced co-assembly was developed to allow the disparate integration of MXene 2D nanosheets into the directive heterogeneities to easily customize the controllable 3D architectures for geometry accessibility, structure integrity, and function adaptability. With functionalized cellulose nanocrystal serving as a structural modifier and cross-linking by polyurethane as well as manipulating the directionally ice templating process, multilevel nanostructured configurations with interconnected porous channels could be obtained for biomimetic aerogel electrodes across multiple length scales. Benefiting from the high ion pathway from the low-tortuosity topology, MXene aerogels showed outstanding electrochemical property (225 F/g), high-rate capacity, and temperature-invariant superelasticity (from 0 to 150 °C), which surpassed some of the best reported values. MXene quasi-solid-state supercapacitors presented superior electrochemistry (energy density: 38.5 μWh/cm²) and outstanding cycle ability (86.7% after 4000 cycles). Exhibiting excellent photoresponse capacity, they could be used as an integrated photodetector. More importantly, specially designed bio-mimicking structures with mechanically self-adaptive resilience could promote MXene 3D aerogels to apply in wearable electronic devices, monitoring various human motions. This work will shed light on MXene aerogels for smart and self-powered lightweight electronics.

Advances in the Synthesis of 2D MXenes

2D transition metal carbides, nitrides, and carbonitrides, also known as MXenes, are versatile materials due to their adjustable structure and rich surface chemistry. The physical and chemical diversity has recognized MXenes as a potential 2D material with a wide spectrum of application domains. Since the discovery of MXenes in 2011, a wide variety of synthetic routes has been proposed with advancement toward large-scale preparing methods for MXene nanosheets and derivative products. Herein, the critical synthesis aspects and the operating conditions that influence the physical and chemical characteristics of MXenes are discussed in detail. The emerging etching methods including HF etching methods, in situ HF-forming etching methods, electrochemical etching methods, alkali etching methods, and molten salt etching methods, as well as delamination strategies are discussed. Considering the future developments and practical applications, the large-scale synthesis routes and the antioxidation strategies of MXenes are also summarized. In summary, a generalized overview of MXenes synthesis protocols with an outlook for the current challenges and promising technologies for large-scale preparation and stable storage is provided.

Black phosphorene/blue phosphorene van der Waals heterostructure: a potential anode material for lithium-ion batteries

Van der Waals (vdW) heterostructure-based electrodes have invoked tremendous research interest due to their intriguing properties and their capability to break the limitations of the restricted properties of single-material systems. Herein, based on first-principles approaches, we propose that the black phosphorene/blue phosphorene (BLK-P/BLE-P) vdW heterostructure can be a capable anode material for power-driving lithium-ion batteries (LIBs), as it exhibits a large theoretical capacity, together with a relatively strong binding strength compared with the individual BLK-P and BLE-P monolayers. Our calculation results show that the Li adatom prefers to intercalate into the interlayer of the BLK-P/BLE-P vdW heterostructure due to the synergistic interfacial effect, resulting in a high binding strength and a diffusivity comparable to the BLK-P and BLE-P monolayers. Subsequently, the theoretical specific capacity is found to be as high as 552.8 mA h g^-1, which can be attributed to the much higher storage capacity of Li adatoms in the BLK-P/BLE-P vdW heterostructure. Furthermore, electronic structure calculations reveal that a large amount of charge transfer assists in semiconductor to metallic transition upon lithiation, which would ensure good electrical conductivity. These simulations prove that the BLK-P/BLE-P heterostructure has great potential in LIBs and is essential for future battery design.

Recent Progress of Two-Dimensional Materials for Ultrafast Photonics

Owing to their extraordinary physical and chemical properties, two-dimensional (2D) materials have aroused extensive attention and have been widely used in photonic and optoelectronic devices, catalytic reactions, and biomedicine. In particular, 2D materials possess a unique bandgap structure and nonlinear optical properties, which can be used as saturable absorbers in ultrafast lasers. Here, we mainly review the top-down and bottom-up methods for preparing 2D materials, such as graphene, topological insulators, transition metal dichalcogenides, black phosphorus, and MXenes. Then, we focus on the ultrafast applications of 2D materials at the typical operating wavelengths of 1, 1.5, 2, and 3 μm. The key parameters and output performance of ultrafast pulsed lasers based on 2D materials are discussed. Furthermore, an outlook regarding the fabrication methods and the development of 2D materials in ultrafast photonics is also presented.

First-Principles Evaluation of Volatile Organic Compounds Degradation in Z-Scheme Photocatalytic Systems: MXene and Graphitic-CN Heterostructures

It is a formidable challenge to use the traditional trial-and-error method to identify suitable catalysts for the photocatalytic degradation of volatile organic compounds (VOCs). In this work, by performing density functional theory calculations, we designed three Z-scheme g-CN/M₂CO₂ (M = Hf, Zr, and Sc) heterostructures, which not only exhibit favorable structure stability but also show promising ability for photocatalytic degradation of VOCs. The enhancement of the photocatalytic activity of these three Z-scheme systems can be ascribed to the low recombination rate of electron-hole pairs because photoelectrons migrated from the g-CN layer to the M₂CO₂ layer as well as the internal electric fields in the Z-scheme heterojunction. Among the three heterostructures, only g-CN/Zr₂CO₂ presents favorable spectra utilization under photoirradiation as well as the direct band gap. As a result, in the Z-scheme g-CN/Zr₂CO₂ heterostructure, the electrons in the conduction band of g-CN migrate to the holes in the valence band of the Zr₂CO₂ layer, which improves extraction and utilization of photogenerated electrons in the g-CN sheet. Moreover, the Z-scheme g-CN/Zr₂CO₂ system shows superior performance for photocatalytic VOC degradation in comparison with individual g-CN and Zr₂CO₂, which can be attributed to the enhanced VOC adsorption capacity as well as excellent ability to photoactivate O₂ and H₂O into ^•O₂^- and ^•OH radicals. Our findings pave a new promising way to facilitate the application of MXene-based materials for VOC photocatalytic degradation.

A V3C2MXene/graphene heterostructure as a sustainable electrode material for metal ion batteries

Individually, MXene and graphene based frameworks have been recognized as promising 2D electrode materials for metal ion batteries. Herein, we have engineered a heterostructure of V₃C₂MXene and graphene using computational design. A comprehensive investigation of designed heterostructure has been reported in this work. Simulated heterostructure has been evaluated for various functionalities such as high performance of thermal stability, metal ion intercalation, diffusion energy using density functional theory method. Interestingly, simulation examinations and obtained calculations demonstrate the high storage capacity of Li and Ca (598.63 mAh g^-1), and Na (555.87 mAh g^-1) with the designed V₃C₂/graphene model. Promising diffusion energy barriers for Li (0.11 eV), Na (0.17 eV) and Ca (0.15 eV) ions are also investigated and have explained systematically in the present work. Moreover, we have achieved high capacity and fast charge/discharge rates of V₃C₂/graphene heterostructure indicating its promising electrode potential efficiency for ion batteries especially for Na ion battery. Thus, our investigation demonstrate the advantages of newly designed V₃C₂MXene and graphene heterostructure for advance metal ion batteries.

Computational insights into modulating the performance of MXene based electrode materials for rechargeable batteries

MXene, a still-growing large family of two-dimensional (2D) materials, has aroused enormous attention in the scientific community. Owing to their high specific surface area, good electronic conductivity, stability, and hydrophilicity, MXene has found a wide application involving electromagnetic interference shielding, sensors, catalysis, and energy storage, etc. In the field of energy storage, MXenes are promising electrode materials for various metal-ion batteries and they are also effective anchoring materials for Li-S batteries. One of the most unique features of MXene is its abundant compositions, which renders us large room to modulate its properties. Besides, other effective approaches applicable to traditional 2D materials can also be used to optimize the performance of MXene. Theoretical calculations have played a significant role in predicting and screening high-performance MXene based electrode materials. So far, theoretical researchers have made much progress in optimizing the performance of MXene as electrode materials for various rechargeable batteries. In the present review, started by a brief introduction of the involved mechanism and basic calculation methods, we comprehensively overview the latest theoretical studies of modulating the performance of MXene based electrode materials for rechargeable batteries.

Nb2CTx MXene as High-Performance Energy Storage Material with Na, K, and Liquid K-Na Alloy Anodes

Two-dimensional MXenes perform well as hosts in batteries, which are promising for next-generation energy storage materials. With low price and high performance, sodium (Na) and potassium (K) own the potential to replace lithium in energy storage devices, but the larger radii and dendrite growth restrict their commercialization. Herein, we successfully synthesized an accordion-like Nb₂CT_x MXene, whose crystal structure integrity and lamellar separation have been confirmed by characterization methods like high-resolution transmission electron microscopy (HR-TEM). Combined with solid Na and K and liquid K-Na alloy as anodes, the Nb₂CT_x MXene shows excellent electrochemical performance, such as high capacity retention after large current shock in tests of rate performance and long time stability for more than 500 cycles, etc. Also, the Nb₂CT_x MXene coupled with liquid K-Na anode performs better than that coupled with solid K for the dendrite-controlling character of the liquid electrode. The Nb₂CT_x MXene would boost the exploitation of more suitable host materials for Na/K-ion batteries and promote an in-depth understanding of MXenes.

Exploring the Efficient Na/K Storage Mechanism and Vacancy Defect-Boosted Li+ Diffusion Based on VSe2/MoSe2 Heterostructure Engineering

As typical 2D materials, VSe₂ and MoSe₂ both play a complementary role in Li/Na/K storage. Therefore, we designed and optimized the VSe₂/MoSe₂ heterostructure to gain highly efficient Li/Na/K-ion batteries. Most importantly, achieving fast Li/Na/K-ion diffusion kinetics in the interlayer of VSe₂/MoSe₂ is a key point. First of all, first-principles calculations were carried out to systematically investigate the packing structure, mechanical properties, band structure, and Li/Na/K storage mechanism. Our calculated results suggest that a large interlayer spacing (3.80 Å), robust structure, and metallic character pave the way for achieving excellent charge-discharge performance for the VSe₂/MoSe₂ heterostructure. Moreover, V and Mo ions both suffer a very mild redox reaction even if Li/Na/K ions fill the interlayer space. These structures were all further verified to show thermal stability (300 K) by means of the AIMD method. By analyzing the Li/Na/K diffusion behavior and the effect of vacancy defect on the structural stability and energy barrier for Li interlayer diffusion, it is found that the VSe₂/MoSe₂ heterostructure exhibits very low-energy barriers for Na/K interlayer diffusion (0.21 eV for Na and 0.11 eV for K). Compared with the VSe₂/MoSe₂ heterostructure, the V_0.92Se_1.84/MoSe₂ heterostructure not only can still maintain a stable structure and metallic character but also has much lower energy barrier for Li interlayer diffusion (0.07 vs 0.48 eV). These discoveries also break new ground to eliminate the obstacles preventing Li⁺ diffusion in the interlayer of other heterostructure materials. Besides, both VSe₂/MoSe₂ and V_0.92Se_1.84/MoSe₂ heterostructures have low average open-circuit voltage (OCV) values during Li/Na/K interlayer diffusion (1.07 V for V_0.92Se_1.84/MoSe₂ vs Li⁺, 0.86 V for VSe₂/MoSe₂ vs Na⁺, and 0.54 V for VSe₂/MoSe₂ vs K⁺), such low OCV values are beneficial for anode materials with excellent electrochemical properties. The above findings offer a new route to design anode materials for Li/Na/K-ion batteries.

A high-throughput assessment of the adsorption capacity and Li-ion diffusion dynamics in Mo-based ordered double-transition-metal MXenes as anode materials for fast-charging LIBs

Utilizing the latest SCAN-rVV10 density functional, we thoroughly assess the electrochemical properties of 35 Mo-based ordered double transition metal MXenes, including clean Mo2MC2 (M = Sc, Ti, V, Zr, Nb, Hf, Ta) and surface functionalized structures Mo2MC2T2 (T = H, O, F and OH), for the potential use as anode materials in lithium ion batteries (LIBs). The first principles molecular dynamics simulations in combination with the calculations of the site adsorption preferences for Li atoms on all investigated MXenes reveal that both Li-saturated adsorption structures and theoretical capacities of Mo-based MXenes are fundamentally influenced by the surface terminations. We find that the adsorption of Li atoms on either -OH or -F functionalized MXenes is chemically unstable. In particular, the F-groups prefer to form a separate fluoride layer with Li atoms, detaching from the Mo2MC2 substrates. The Li atoms could form a stable single adsorption layer on the -H, -O and intrinsic MXenes surface, exhibiting theoretical capacities in the range from 121 mA h g-1 to 195 mA h g-1. Besides -F and -OH terminations, the remaining Mo-based MXenes also possess superior flat open circuit voltage (OCV) profiles with the most reversible storage capacity below 1.0 V during the charging/discharging cycles. We further predict the low barrier heights of Li-ion diffusion, at a range of 0.03-0.06 eV for most Mo-based MXenes except -O and -H terminations, exceeding that of graphene or Ti3C2. Furthermore, combining the Vineyard transition state theory (TST) with the phonon spectra obtained from density functional perturbation theory (DFPT), the mean planar diffusion coefficient is calculated to be 2 × 10-8 m2 s-1 at 300 K for intrinsic Mo2MC2 monolayers. Although the overall specific capacity is fundamentally restricted with the relatively heavy molecular mass of MXenes, we conclude that Mo-based structures, especially the intrinsic Mo2MC2 (M = Sc, Ti, V) monolayers, might be promising anode materials from the aspect of fast charging/discharging application for LIBs.

Two-dimensional graphene-HfS2 van der Waals heterostructure as electrode material for alkali-ion batteries

Poor electrical conductivity and large volume expansion during repeated charge and discharge is what has characterized many battery electrode materials in current use. This has led to 2D materials, specifically multi-layered 2D systems, being considered as alternatives. Among these 2D multi-layered systems are the graphene-based van der Waals heterostructures with transition metal di-chalcogenides (TMDCs) as one of the layers. Thus in this study, the graphene–hafnium disulphide (Gr–HfS₂) system, has been investigated as a prototype Gr–TMDC system for application as a battery electrode. Density functional theory calculations indicate that Gr–HfS₂ van der Waals heterostructure formation is energetically favoured. In order to probe its battery electrode application capability, Li, Na and K intercalants were introduced between the layers of the heterostructure. Li and K were found to be good intercalants as they had low diffusion barriers as well as a positive open circuit voltage. A comparison of bilayer graphene and bilayer HfS₂ indicates that Gr–HfS₂ is a favourable battery electrode system.

A high rate capacity, moderate volume expansion and energetically stable alkali ion graphene–HfS₂ electrode material.

High-Performance Electrocatalytic Conversion of N2 to NH3 Using 1T-MoS2 Anchored on Ti3C2 MXene under Ambient Conditions

Herein, 1T-MoS₂ nanospots assembled on conductive Ti₃C₂ MXene (1T-MoS₂@Ti₃C₂) are first developed to regard as efficient electrocatalytic nitrogen fixation catalysts with high selectivity. The 1T-MoS₂@Ti₃C₂ composite exhibits outstanding NRR activity with a faradic efficiency (FE) of 10.94% and a NH₃ yield rate of 30.33 μg h^-1 mg^-1_cat. at -0.3 V versus RHE. Notably, the 1T-MoS₂@Ti₃C₂ composite displays excellent stability and durability during the recycling test. The outstanding NRR catalytic activity is primarily attributed to the synergy effect between 1T-MoS₂ and Ti₃C₂ MXene. In addition, the isotopic experiment confirms the synthesized NH₃ deriving from the conversion of the supplied nitrogen.

Strain-engineered BlueP-MoS2 van der Waals heterostructure with improved lithiation/sodiation for LIBs and SIBs

Innovative van der Waals (vdW) heterostructures formed from various monolayers exhibit exceptional physical properties relevant to their corresponding individual layers. In addition, the strain engineering of 2D materials is significantly exciting because they have the potential to sustain much larger strain in comparison to their bulk counterparts. In this work, the influence of strain on a BlueP-MoS2 van der Waals heterostructure was studied in order to explore its performance in LIBs/SIBs by first-principles DFT calculations. To ascertain the influence of strain on the performance of the BlueP-MoS2 van der Waals heterostructure for electrodes in LIBs/SIBs, we gathered vertically aligned monolayers of MoS2 and BlueP with different amounts of strain and studied the Li/Na storage properties of the said material. The application of strain could effectively enhance the adsorption capability of both Li/Na at the surfaces/interface of the BlueP-MoS2 heterostructure in comparison to that of the pristine BlueP-MoS2 heterostructure along with improved storage capacity. On the other hand, the application of strain is robust to the high mobility of both Li/Na inside and outside surfaces of BlueP-MoS2 heterostructure which ensures the fast charge/discharge process and improved rate performance. The calculated electronic structure revealed that the applied strain converted the BlueP-MoS2 heterostructure from a semiconductor to a metal, indicating enhanced conductivity compared to that for the pristine BlueP-MoS2 heterostructure. All the above-mentioned findings suggest the high potential application of the BlueP-MoS2 vdW heterostructures for flexible nanoelectronic devices.

Spring-roll-like Ti3C2 MXene/carbon-coated Fe3O4 composite as a long-life Li-ion storage material

Fe₃O₄ is a promising anode material for Li-ion batteries because of its high theoretical capacity, low cost, and natural abundance.

Modulation engineering of 2D MXene-based compounds for metal-ion batteries

The increasing demand for next generation rechargeable metal-ion batteries (MIBs) has boosted the exploration of high-performance electrode materials. Two-dimensional (2D) transition metal carbides/nitrides (MXenes), the largest family of 2D materials, show extremely competitive potential applications in electrodes due to their excellent electrical conductivity, chemical diversity, and large specific surface area. However, the problems of uncontrollable surface functionalization, interlayer restack and collapse significantly hinder their practical applications. To this end, effective strategies to modify traditional MXenes for targeted electrochemical performance are highly desirable. In this mini review, we briefly summarize the most recent and constructive development in the modulation engineering of 2D MXene-based transition-metal compounds. Firstly, to modify traditional MXenes by intercalating, surface decorating and constructing heterostructures. Secondly, to design novel transition-metal compounds beyond MXenes by precisely controlling the atomic structures, proportions and compositions of constituent elements. Moreover, the critical challenges and perspectives for future research on MXene-based materials are also presented.

In Situ Fabricating Oxygen Vacancy-Rich TiO2 Nanoparticles via Utilizing Thermodynamically Metastable Ti Atoms on Ti3C2Tx MXene Nanosheet Surface To Boost Electrocatalytic Activity for High-Performance Li-O2 Batteries

Catalysts with high performance are urgently needed in order to accelerate the reaction kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in lithium-oxygen (Li-O₂) batteries. Herein, utilizing thermodynamically metastable Ti atoms on the Ti₃C₂Tx MXene nanosheet surface as the nucleation site, oxygen vacancy-rich TiO₂ nanoparticles were in situ fabricated on Ti₃C₂Tx nanosheets (V-TiO₂/Ti₃C₂Tx) and used as the oxygen electrode of Li-O₂ batteries. Oxygen vacancy (Vo) can boost the migration rate of electrons and Li⁺ as well as act as the active sites for catalyzing the ORR and OER. Based on the above merits, V-TiO₂/Ti₃C₂Tx-based Li-O₂ battery shows improved performance including the ultralow overpotential of 0.21 V, high specific capacity of 11 487 mA h g^-1 at a current density of 100 mA g^-1, and excellent round-trip efficiency (93%). This work proposes an effective strategy for researching high-performance oxygen electrodes for Li-O₂ batteries via introducing Vo-rich oxides on two-dimensional MXene.