Latest ArticlesElectrochemical reduction of N2, as an eco-friendly alternative, not only allows the use of protons in water as a source of hydrogen under mild conditions but also can be driven by renewable electric energy. The major challenge is to identify high-efficiency electrocatalysts. MXene is a new class of 2D transition metal carbides, nitrides, and carbonitrides that have received significant attention in electrocatalysis. The investigations on MXene in electrocatalytic nitrogen fixation are rapidly proceeding, and some breakthroughs have emerged very recently due to MXenes' satisfactory catalytic activity. Here, the recent progress concerning the MXene-based catalysts for electrochemical N2 reduction reaction (NRR) is highlighted. In regards to giving guidelines for exploring more efficient MXene-based catalysts for the NRR, the fabrication and surface modification of MXene are discussed. Besides, the shortcomings and challenges of current research are summarized and the future research directions are prospected.
Combining high conductivity, hydrophilicity and excellent electrochemical performance in one, MXenes have attracted increasing attention since their inception. However, easy to stack caused by the van der Waals' force between the layers limits their practical application. Fortunately, intercalating other substances between layers of MXenes and getting intercalated MXene-based layered composites (IMLCs) with open structure can improve their physical and chemical properties effectively. Larger available surface helps expose more active sites and enlarged layer spacing facilitates ion transport. In addition, other substances fixed in the interlayers by MXenes' two-dimensional confinement effect can produce synergistic effect and expand their applicable range greatly. This review is dedicated to summarizing the preparation methods and applications of IMLCs, emphasizing the advantages of them in the fields of energy storage, catalysis, sensors, electromagnetic interference (EMI) shielding and biomedicine. Furthermore, prospects and further developments in these gratifying fields are also commented.
The geometrically multiplied development of 2D MXenes has already promoted the prosperity of various fields of scientific researches especially but not limited in energy storage and conversion. Notably, cation intercalation can improve the interlayer spacing of MXenes resulting in tunable physical and chemical properties. Moreover, the synchrotron radiation X-ray characterizations have also shown high potential on exploring the property and structure of cation intercalated MXenes. This review is mainly focused on the recent achievements of cation intercalated MXenes through different methods on energy storage systems. Synchrotron-based X-ray absorption spectroscopic characterizations are emphasized to probe the local coordination and electronic structure in intercalated MXenes. The outlook of cation intercalation on MXenes and their applications are also discussed.
Available onlineSilicon monoxide (SiO) is a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical specific capacity (~2400 mAh/g), low working potential (< 0.5 V vs. Li+/Li), low cost, easy synthesis, nontoxicity, abundant natural source and smaller volume expansion than Si. However, low intrinsic electrical conductivity, low initial Coulombic efficiency (ICE) and inevitable volume expansion (~200%) impede its practical application. Here we fabricate SiO/wrinkled MXene composite (SiO-WM) by an electrostatic self-assembly method. Importantly, this method is simple, scalable and taking into account all the issues of SiO. As a result, the SiO-WM exhibits improved rate capability, cycling performance and ICE than bare SiO.
In this study, two-dimensional V2CTx MXene has been prepared by selectively etching Al layers from V2AlC MAX phase by NaF+HCl etching at 90 ℃ for 72 h and its performance as supercapacitor (SC) electrode were tested using simulating seawater as electrolyte. V2CTx MXene-based electrodes shows a good capacitance of 181.1 F/g, which is in accordance with the volumetric specific capacitance of 317.8 F/cm3, and with 89.1% capacitance retention even after 5000 cycle. Compared with other MXenes, V2CTx have better electrochemical performance as SC electrode. This work provides an innovative strategy to apply V2CTx MXene as SC electrode in safety and effective seawater electrolyte.
Designing efficient electrocatalysts with low Pt loadings for hydrogen evolution reaction (HER) is urgently required for renewable and sustainable energy conversion. Here, we report a strategy that Pt nanoparticulates are spontaneously immobilized on porous MXene/MAX monolith as HER catalysts by utilizing the redox reaction between Ti3C2Tx MXene and [PtCl4]2- in H2PtCl6 aqueous solution. By taking advantage of homogeneously distributed Pt nanoparticulates on highly electrically conductive porous Ti3C2Tx/Ti3AlC2 monolith, the as-prepared electrocatalysts show high catalytic performance for hydrogen evolution. Specifically, the binder-free electrocatalysts have Pt loadings as low as 8.9 μg/cm2, with low overpotential of 43 mV at a current density of 10 mA/cm2 and low Tafel slope that three times lower than porous Ti3C2Tx/Ti3AlC2 without Pt loading. This strategy offers a new approach to constructing ultra-low Pt-loading HER catalysts on the basis of in situ redox reaction between noble metal ions and MXenes.
The problem of water pollution has become increasingly serious, and it has already threatened the survival of mankind and has become an obstacle to the healthy development of human health. Here, we prepared a novel polyvinyl alcohol (PVA)/polyacrylic acid (PAA)/MXene fiber membrane by electrospinning. After heat treatment of film and subsequent modification with Pd nanoparticles, PVA/PAA/MXene@PdNPs composite nanofiber membrane with high specific surface area and excellent catalytic performance was finally prepared. The uniform distribution of MXene sheets in the composite fiber membrane not only solves the problem that the MXene sheet is not easy to be monolayerized, but also can grow the self-reduced Pd nanoparticles on the MXene sheets. In addition, the composite nanofiber membrane exhibits excellent catalytic ability and cycle stability for 4-nitrophenol (4-NP) and 2-nitrophenol (2-NA), providing new strategy for the study of catalytic composite materials related to degradation of wastewater.
Two-dimensional (2D) Ti3C2Tx MXene is an attractive additive not only used in base oil due to its low friction coefficient, but also used in composites due to its high aspect ratio and rich surface functional groups. So far there has been intense research into polymer matrix composites reinforced with Ti3C2Tx. Here we report on the use of 2D Ti3C2Tx to enhance the mechanical and frictional properties of Al matrix composites. Ti3C2Tx/Al composites were designed and prepared by pressureless sintering followed by hot extrusion technique. The prepared composites exhibit a homogeneous distribution of Ti3C2Tx. The Vickers hardness and the tensile strength continuously increase with increasing Ti3C2Tx content. A hardness of 0.52 GPa and a tensile strength of 148 MPa were achieved in the 3 wt% Ti3C2Tx/Al composite. The frictional properties of pure Al and the Ti3C2Tx/Al composite were comparably studied under dry sliding. A low friction coefficient of 0.2, twice lower than that of pure Al, was achieved in the 3 wt% Ti3C2Tx/Al composite. Ti3C2Tx acting as a solid lubricant reduces the abrasive wear in the composite, improving the frictional properties of Al matrix composites.
Ti3C2 belongs to MXenes family, which is a new two-dimensional material and has been applied in many fields. With simple method of hydrothermal and high temperature calcination, nanostructured Ni/Ti3C2Tx hybrid was synthesized. The stable layer structure of Ti3C2 MXene providing high surface area as well as excellent electronic conductivity are beneficial for deposition and decomposition of discharge product Li2O2. Furthermore, possessing special catalytic activity, Ni nanoparticles with size of about 20 nm could accelerate Li2O2 breaking down. Taking advantage of two kinds of materials, Ni/Ti3C2Tx hybrid as cathode of Li-O2 battery can achieve a maximal specific capacity of 20, 264 mAh/g in 100 mA/g and 10, 699 mAh/g in 500 mA/g at the first cycle. This work confirms that the prepared Ni/Ti3C2Tx hybrid exhibiting better cycling stability points out a new guideline to improve the electrochemical performance of lithium-oxygen batteries.
MXene-based electrode materials exhibit favorable supercapacitor performance in sulfuric acid due to praised pseudocapacitance charge storage mechanism. However, self-stacking of conventional MXene electrodes severely restricts their electrochemical performance, especially at high loading. Herein, a flexible cross-linked porous Ti3C2Tx-MXene-reduced graphene oxide (Ti3C2Tx-RGO) film is skillfully designed and synthesized by microscopic explosion of graphene oxide (GO) at sudden high temperature. The generated chamber structure between layers could hold a few of electrolyte, leading to a close-fitting reaction at interlayer and avoiding complex ions transmission paths. The Ti3C2Tx-RGO film displayed a preferable rate performance than that of pure Ti3C2Tx film and a high capacitance of 505 F/g at 2 mV/s. Furthermore, the uniform intralayer structure and unique energy storage process lead to thickness-independenct electrochemical performances. This work provides a simple and feasible improvement approach for the design of MXene-based electrodes, which can be spread other electrochemical systems limited by ions transport, such as metal ions batteries and catalysis.
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