MXene Film Prepared by Vacuum-Assisted Filtration: Properties and Applications

Mechanical properties of two-dimensional material-based thin films: a comprehensive review

Two-dimensional (2D) materials are materials with a thickness of one or a few atoms with intriguing electrical, chemical, optical, electrochemical, and mechanical properties. Therefore, they are deemed candidates for ubiquitous engineering applications. Films and three-dimensional (3D) structures made from 2D materials introduce a distinct assembly structure that imparts the inherent properties of pristine 2D materials on a macroscopic scale. Acquiring the adequate strength and toughness of 2D material structures is of great interest due to their high demand for numerous industrial applications. This work presents a comprehensive review of the mechanical properties and deformation behavior of robust films composed of 2D materials that help them to attain other extraordinary properties. Moreover, the various key factors affecting the mechanical performance of such thin films, such as the lateral size of nanoflakes, fabrication technique of the film, thickness of the film, post-processing, and strain rate, are elucidated.

Layered MXene Films via Self-Assembly

MXene has attracted significant attention as a 2D material family due to its metallic conductivity and abundant surface functional groups and has been extensively studied and applied as bulk materials and microscale thin films. MXene possesses ionizable surfaces and edges, as well as high surface area. Its customizable dispersibility demonstrates unique advantages in self-assembly solution processing. Recent studies have demonstrated the application value of layered MXene films at the nanoscale thickness and the reliance of processing on self-assembly techniques. However, this field currently lacks sufficient attention. Here, the regulatory mechanisms are summarized for the preparation of layered MXene films through self-assembly techniques, as well as introduce their applications. Moreover, the future challenges of large-scale applications of MXene self-assembly techniques are proposed. It is believed that this review would provide a dynamic and promising path for the development of layered MXene self-assembly techniques.

MXene film electrodes with high mechanical strength, graded ion channels and high pseudocapacitive activity enabled by lignin-containing cellulose fibers

Cellulose nanofiber (CNF) has been widely used in MXene film electrodes to improve its mechanical properties and rate capability for supercapacitors. However, all the above enhancements are obtained with inevitably sacrificing the capacitance, because of the non-electrochemically-active characteristic of CNF. Herein, to address this issue, lignin-containing cellulose fibers (LCNF) is innovatively used to substitute CNF. Specifically, LCNF play a role as a bridge to significantly reinforce mechanical strength of LCNF/MXene film electrode (LM) by binding the adjacent MXene nanosheets, reaching a tensile strength of 34.2 MPa. Lignin in LCNF contributes to pseudocapacitance through the reversible conversion of its quinone/hydro-quinone (Q/QH2), thus yielding an excellent capacitance of 364.4 F g-1 at 1 A g-1. Meanwhile, LCNF has different diameters in which microfibers form a loose structure for LM, nanofibers enlarge d-spacing between adjacent MXene nanosheets, and fibers self-crosslinking creates abundant pores, thus constructing graded channels to achieve an outstanding rate capability of 87 % at 15 A g-1. The fabricated supercapacitor demonstrates a large energy density of 1.8 Wh g-1 at 71.3 W g-1. This work provides a promising approach to decouple the trade-off between electrochemical performance and mechanical properties of MXene film electrodes caused by using CNF, thus obtaining high-performance supercapacitors.

Self-standing membranes for separation: Achievements and opportunities

Supported membranes and mixed matrix membranes have a limitation of harming the mass transfer due to the incompatibility between the support layer or the matrix and the active components of the membrane. Self-standing membranes, which could structurally abandon the support layer, altogether avoid the adverse effect, thus greatly facilitating the transmembrane mass transfer process. However, the abandonment of the support layer also reduces the membrane's mechanical properties and formability. In this review, our emphasis will be on self-standing membranes within the realm of materials and separation engineering. We will explore the materials employed in the fabrication of self-standing membranes, highlighting their ability to simultaneously enhance membrane performance and promote self-standing characteristics. Additionally, we will delve into the diverse techniques utilized for crafting self-standing membranes, encompassing interfacial polymerization, filtration, solvent casting, Langmuir-Blodgett & layer-by-layer assembly, electrospinning, compression, etc. Throughout the discussion, the merits and drawbacks associated with each of these preparation methods were elucidated. We also provide a brief overview of the applications of self-standing membranes, including water purification, gas separation, organic solvent nanofiltration, electrochemistry, and membrane reactor, as well as a brief description of the general strategies for performance enhancement of self-standing membranes. Finally, the current status of self-standing membranes and the challenges they may encounter were discussed.

The dawn of MXene duo: revolutionizing perovskite solar cells with MXenes through computational and experimental methods

Integrating MXene into perovskite solar cells (PSCs) has heralded a new era of efficient and stable photovoltaic devices owing to their supreme electrical conductivity, excellent carrier mobility, adjustable surface functional groups, excellent transparency and superior mechanical properties. This review provides a comprehensive overview of the experimental and computational techniques employed in the synthesis, characterization, coating techniques and performance optimization of MXene additive in electrodes, hole transport layer (HTL), electron transport layer (ETL) and perovskite photoactive layer of the perovskite solar cells (PSCs). Experimentally, the synthesis of MXene involves various methods, such as selective etching of MAX phases and subsequent delamination. At the same time, characterization techniques encompass X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy, which elucidate the structural and chemical properties of MXene. Experimental strategies for fabricating PSCs involving MXene include interfacial engineering, charge transport enhancement, and stability improvement. On the computational front, density functional theory calculations, drift-diffusion modelling, and finite element analysis are utilized to understand MXene's electronic structure, its interface with perovskite, and the transport mechanisms within the devices. This review serves as a roadmap for researchers to leverage a diverse array of experimental and computational methods in harnessing the potential of MXene for advanced PSCs.

Molten salt-shielded synthesis of Ti3AlC2 as a precursor for large-scale preparation of Ti3C2Tx MXene binder-free film electrode supercapacitors

MXenes are a group of two-dimensional materials that are promising for many applications, including as film electrode supercapacitors. When synthesizing such materials, special attention is paid to the conditions for obtaining the MAX phase, the chemical, morphological and structural features of which determine the functional properties of the final product. In this study, the Ti3AlC2 precursor is proposed to be obtained using a technologically simple and accessible method of synthesis in molten salt. This method allows reducing the reaction temperature and creating an antioxidant atmosphere. Ti3C2Tx MXene electrode films are produced by the easily scalable blade coating method without a binder. The synthesized materials were studied by X-ray phase analysis and scanning electron microscopy. Electrochemical testing of Ti3C2Tx film electrodes was carried out in a three-electrode configuration in aqueous solutions of 1M H2SO4, 6M KOH, 1M LiOH and 1M Na2SO4 electrolytes. The maximum specific capacity value for Ti3C2Tx MXene binder-free film electrode supercapacitors is obtained in 1M H2SO4 electrolyte (480 F g-1 at a scan rate of 1 mV s-1). The simple, low-cost and scalable production technology and promising electrochemical characteristics of the Ti3C2Tx MXene binder-free film electrode make it an excellent candidate for new-generation supercapacitors.

MXene-based electrochemical devices applied for healthcare applications

The initial part of the review provides an extensive overview about MXenes as novel and exciting 2D nanomaterials describing their basic physico-chemical features, methods of their synthesis, and possible interfacial modifications and techniques, which could be applied to the characterization of MXenes. Unique physico-chemical parameters of MXenes make them attractive for many practical applications, which are shortly discussed. Use of MXenes for healthcare applications is a hot scientific discipline which is discussed in detail. The article focuses on determination of low molecular weight analytes (metabolites), high molecular weight analytes (DNA/RNA and proteins), or even cells, exosomes, and viruses detected using electrochemical sensors and biosensors. Separate chapters are provided to show the potential of MXene-based devices for determination of cancer biomarkers and as wearable sensors and biosensors for monitoring of a wide range of human activities.

A Review of Manufacturing Methods for Flexible Devices and Energy Storage Devices

Given the advancements in modern living standards and technological development, conventional smart devices have proven inadequate in meeting the demands for a high-quality lifestyle. Therefore, a revolution is necessary to overcome this impasse and facilitate the emergence of flexible electronics. Specifically, there is a growing focus on health detection, necessitating advanced flexible preparation technology for biosensor-based smart wearable devices. Nowadays, numerous flexible products are available on the market, such as electronic devices with flexible connections, bendable LED light arrays, and flexible radio frequency electronic tags for storing information. The manufacturing process of these devices is relatively straightforward, and their integration is uncomplicated. However, their functionality remains limited. Further research is necessary for the development of more intricate applications, such as intelligent wearables and energy storage systems. Taking smart wear as an example, it is worth noting that the current mainstream products on the market primarily consist of bracelet-type health testing equipment. They exhibit limited flexibility and can only be worn on the wrist for measurement purposes, which greatly limits their application diversity. Flexible energy storage and flexible display also face the same problem, so there is still a lot of room for development in the field of flexible electronics manufacturing. In this review, we provide a brief overview of the developmental history of flexible devices, systematically summarizing representative preparation methods and typical applications, identifying challenges, proposing solutions, and offering prospects for future development.

Biomass-Derived Flexible Carbon Architectures as Self-Supporting Electrodes for Energy Storage

With the swift advancement of the wearable electronic devices industry, the energy storage components of these devices must possess the capability to maintain stable mechanical and chemical properties after undergoing multiple bending or tensile deformations. This circumstance has expedited research efforts toward novel electrode materials for flexible energy storage devices. Nonetheless, among the numerous materials investigated to date, the incorporation of metal current collectors or insulative adhesives remains requisite, which entails additional costs, unnecessary weight, and high contact resistance. At present, biomass-derived flexible architectures stand out as a promising choice in electrochemical energy device applications. Flexible self-supporting properties impart a heightened mechanical performance, obviating the need for additional binders and lowering the contact resistance. Renewable, earth-abundant biomass endows these materials with cost-effectiveness, diversity, and modulable chemical properties. To fully exploit the application potential in biomass-derived flexible carbon architectures, understanding the latest advancements and the comprehensive foundation behind their synthesis assumes significance. This review delves into the comprehensive analysis of biomass feedstocks and methods employed in the synthesis of flexible self-supporting carbon electrodes. Subsequently, the advancements in their application in energy storage devices are elucidated. Finally, an outlook on the potential of flexible carbon architectures and the challenges they face is provided.