First principles insights into stability of defected MXenes in water
First principles molecular dynamics reveals how different types of defects on the Ti 3 C 2 T x MXene surface influence its interaction with water.
Chemistry↗
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In Situ Formation of Ripplocations in Hybrid Organic–Inorganic MXenes
Abstract Inorganic–organic hybrid MXenes (h‐MXenes) are a family of 2D transition metal carbides and nitrides functionalized with alkylimido and alkylamido surface groups. Using cryogenic and room temperature scanning transmission electron microscopy (STEM) and electron energy‐loss spectroscopy (EELS), it is shown that ripplocations, a form of a fundamental defect in 2D and layered structures, are abundant in this family of materials. Furthermore, detailed studies of electron probe sample interactions, focusing on structural deformations caused by the electron beam are presented. The findings indicate that at cryogenic temperatures (≈100 K) and below a specific dose threshold, the structure of h‐MXenes remains largely intact. However, exceeding this threshold leads to electron beam‐induced deformation through ripplocations. Interestingly, the deformation behavior, required dose, and resultant structure are highly dependent on temperature. At 100 K, it is demonstrated that the electron beam can induce ripplocations in situ with a high degree of precision.
Chemistry↗
Accelerating Discovery of Atomistic Defects via Machine Learning
The quantification of defects such as vacancies in crystalline structures is a cornerstone of materials science research. Traditional efforts often rely on manual detection, a process that is time-intensive, prone to human error, and challenging to scale. Here we leverage machine learning (ML) methods to identify and quantify vacancies within a crystalline lattice, aiming to expedite detection while improving accuracy. Additionally, we explore the transferability of these ML techniques, identifying characteristics of atomistic imaging data that complicate this task. We show how the integration of ML can drive innovation, providing a powerful tool that will play an increasingly crucial role in the future of materials science.
2D materials↗
Flexible and high-performance electrochromic devices enabled by self-assembled 2D TiO 2 /MXene heterostructures
Transition metal oxides (TMOs) are promising electrochromic (EC) materials for applications such as smart windows and displays, yet the challenge still exists to achieve good flexibility, high coloration efficiency and fast response simultaneously. MXenes (e.g. Ti 3 C 2 T x ) and their derived TMOs (e.g. 2D TiO 2 ) are good candidates for high-performance and flexible EC devices because of their 2D nature and the possibility of assembling them into loosely networked structures. Here we demonstrate flexible, fast, and high-coloration-efficiency EC devices based on self-assembled 2D TiO 2 /Ti 3 C 2 T x heterostructures, with the Ti 3 C 2 T x layer as the transparent electrode, and the 2D TiO 2 layer as the EC layer. Benefiting from the well-balanced porosity and connectivity of these assembled nanometer-thick heterostructures, they present fast and efficient ion and electron transport, as well as superior mechanical and electrochemical stability. We further demonstrate large-area flexible devices which could potentially be integrated onto curved and flexible surfaces for future ubiquitous electronics.
36 MATERIALS SCIENCE↗
Establishing a Theoretical Landscape for Identifying Basal Plane Active 2D Metal Borides (MBenes) toward Nitrogen Electroreduction
Abstract To achieve efficient ammonia synthesis via electrochemical nitrogen reduction reaction (NRR), a qualified catalyst should have both high specific activity and large active surface area. However, integrating these two merits into one single material remains a big challenge due to the difficulty in balancing multiple reaction intermediates. Here, it is demonstrated that the boron‐analogues of MXenes, namely “MBenes”, could cope with the challenge and achieve the high activity and large reaction region simultaneously toward NRR. Using extensive density functional theory computations and taking 16 MBenes as representatives, it is identified that seven MBenes (CrB, MoB, WB, Mo 2 B, V 3 B 4 , CrMnB 2 , and CrFeB 2 ) not only have intrinsic basal plane activity for NRR with limiting potentials ranging from −0.22 to −0.82 V, but also possess superior capability of suppressing the competitive hydrogen evolution reaction. Particularly, different from the MXenes whose surface oxidation may block the active sites, once oxidized, these MBenes can catalyze NRR via the self‐activating process, reducing O*/OH* into H 2 O* under reaction conditions, and favoring the N 2 electroreduction. As a result, the exceptional activity and selectivity, high active area (≈10 19 m −2 ), and antioxidation nature render these MBenes as pH‐universal catalysts for NH 3 production without introducing any dopants and defects.
Guo, Xiangyu↗
MXene binder stabilizes pseudocapacitance of conducting polymers
Unlike conventional additives, the use of MXene as a binder improves the electrochemical performance of conducting polymers. The approach is extendable to a large family of poorly conducting organic materials for sustainable energy storage devices.
Boota, Muhammad↗
Electrical and Elastic Properties of Individual Single-Layer Nb 4 C 3 T x MXene Flakes
2D carbides and nitrides (MXenes) are widely recognized for their exceptional promise for numerous applications. However, physical property measurements of their individual monolayers remain very limited despite their importance for revealing the intrinsic physical properties of MXenes. The first mechanical and electrical measurements of individual single-layer flakes of Nb 4 C 3 T x MXene, which are prepared via an improved synthetic method are reported. Characterization of field-effect transistor devices based on individual single-layer Nb 4 C 3 T x flakes shows an electrical conductivity of 1024 ± 165 S cm -1 , which is two orders of magnitude higher than the previously reported values for bulk Nb 4 C 3 T x assemblies, and an electron mobility of 0.41 ± 0.27 cm 2 V -1 s -1 . Atomic force microscopy nanoindentation measurements of monolayer Nb 4 C 3 T x membranes yield an effective Young's modulus of 386 ± 13 GPa, assuming a membrane thickness of 1.26 nm. This is the highest value reported for nanoindentation measurements of solution-processable 2D materials, revealing the potential of Nb 4 C 3 T x as a primary component for various mechanical applications. In conclusion, the agreement between the mechanical properties of 2D Nb 4 C 3 T x MXene and cubic NbC suggests that the extensive experimental data on bulk carbides could be useful for identifying new MXenes with improved functional characteristics.
36 MATERIALS SCIENCE↗
Rare earth separation in voltage-gated 2D MXene membranes
The separation of rare earth elements (REEs) has historically been a complicated and expensive process, producing significant amounts of pollution. To this end, MXene membranes (MXMs) have attracted researchers' interest. It has been demonstrated that MXMs are capable of separating ions and that it is possible to precisely control the separation rate by applying a voltage to the membrane. Indeed, due to their chemical nature, MXenes show outstanding electrical conductivity. However, the effect of applied voltage on the permeation rate and separation effects of iconic species remains an intriguing area of research. In this work, we demonstrate how applying different voltages (gate voltage) to a MXM affects the permeation rate of various REE ions. Our hypothesis to explain MXMs behavior towards REE is that under negative voltage, the interlayer spacing decreases due to attraction between charged MXene surfaces and intercalated cations, increasing the separation factor between REEs. Under positive voltage, the interlayer spacing increases due to repulsion between the MXene surfaces and intercalated cations. However, we demonstrate relatively poor separation capability for REEs at 1mM starting concentration and 1.0 V applied DC voltage (separation factor ~1-3). This study demonstrates the need for future experiments to observe varied experimental conditions and chemical functionalization to determine whether MXene membranes can be an efficient platform for REE separation.
36 MATERIALS SCIENCE↗
Pseudocapacitance of Vanadium Carbide MXenes in Basic and Acidic Aqueous Electrolytes
Not provided.
Chemistry↗
Nacre-like MXene/Polyacrylic Acid Layer-by-Layer Multilayers as Hydrogen Gas Barriers
MXenes are a promising class of 2D nanomaterials and are of particular interest for gas barrier applications due to their high aspect ratio. However, MXene nanosheets naturally bear a negative charge, which prevents assembly with negatively charged polymers, such as polyacrylic acid (PAA), into gas barrier coatings. Here, we present MXene- and PAA-based layer-by-layer (MXene/ PAA LbL) multilayers formed by leveraging hydrogen bonding interactions. When assembled in acidic conditions, MXene/PAA LbL multilayers exhibit conformal, pinhole-free, nacre-like structures. The MXene/PAA LbL multilayers yield high blocking capability and low permeability (0.14 ± 0.01 cc·mm·m −2 ·day −1 · MPa −1 ) for hydrogen gas which is over 9000 times lower than uncoated niobium (Nb) substrate. These nacre-like structures are also electronically conductive (σ DC , up to 370 ± 30 S cm −1 ). Because these multilayers utilize hydrogen bonding, their properties are highly sensitive to the pH of the assembly and its external environment. Specifically, the reversible deconstruction of these multilayers under basic conditions is experimentally verified. This study shows that hydrogen bonding interactions can be leveraged to form MXene LbL multilayers as gas barriers, electronically conductive coatings, and deconstructable thin films via pH control.
36 MATERIALS SCIENCE↗
Achieving superlubricity with 2D transition metal carbides (MXenes) and MXene/graphene coatings
Not Available
2D materials↗
Tuning the Microenvironment of Water Confined in Ti 3 C 2 T x MXene by Cation Intercalation
Not Available
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Spectroscopic signature of negative electronic compressibility from the Ti core-level of titanium carbonitride MXene
Two-dimensional transition metal carbides, carbonitrides, and nitrides called MXenes exhibit high metallic conductivity, ion intercalation capability and reversible redox activity, prompting their applications in energy storage and conversion, electromagnetic interference (EMI) shielding, and electronics, among many other fields. It has been shown that replacement of about 50% of carbon atoms in the most popular MXene family member, titanium carbide (Ti 3 C 2 T x ), by nitrogen atoms, forming titanium carbonitride (Ti 3 CNT x ), leads to drastically different properties, such as very high negative charge in solution and extreme EMI shielding effectiveness, exceeding all known materials, even metals at comparable thicknesses. Here, by using ultraviolet photoemission spectroscopy (UPS), the electronic structures of Ti 3 CNT x and Ti 3 C 2 T x are systematically investigated and compared as a function of charge carrier density. We observe that, in contrast to Ti 3 C 2 T x , the Ti 3p core-level of Ti 3 CNT x exhibits a counterintuitive shift to a lower binding energy of up to approximately 250 meV upon increasing the electron density, which is a spectroscopic signature of negative electronic compressibility (NEC). These experimentally measured chemical potential shifts are well-captured by the density functional theory (DFT) calculation. The DFT results also further suggest that the hybridization of titanium-nitrogen bonding in Ti 3 CNT x helps promoting the available states of Ti atoms for receiving more electron above the Fermi level and leads to the observed NEC. Furthermore, our findings explain the differences in electronic properties between the two very important and widely studied MXenes and also suggest a new strategy to apply the NEC effect of Ti 3 CNT x in energy and charge storage applications.
2D materials↗
Ultrastrong Ionotronic Films Showing Electrochemical Osmotic Actuation
Abstract A multifunctional soft material with high ionic and electrical conductivity, combined with high mechanical properties and the ability to change shape can enable bioinspired responsive devices and systems. The incorporation of all these characteristics in a single material is very challenging, as the improvement of one property tends to reduce other properties. Here, a nanocomposite film based on charged, high‐aspect‐ratio 1D flexible nanocellulose fibrils, and 2D Ti 3 C 2 T x MXene is presented. The self‐assembly process results in a stratified structure with the nanoparticles aligned in‐plane, providing high ionotronic conductivity and mechanical strength, as well as large water uptake. In hydrogel form with 20 wt% liquid, the electrical conductivity is over 200 S cm −1 and the in‐plane tensile strength is close to 100 MPa. This multifunctional performance results from the uniquely layered composite structure at nano‐ and mesoscales. A new type of electrical soft actuator is assembled where voltage as low as ±1 V resulted in osmotic effects and giant reversible out‐of‐plane swelling, reaching 85% strain.
Chemistry↗