Selective Etching of Silicon from Ti3SiC2 (MAX) To Obtain 2D Titanium Carbide (MXene)

Until now, MXenes could only be produced from MAX phases containing aluminum, such as Ti₃AlC₂. Here, we report on the synthesis of Ti₃C₂ (MXene) through selective etching of silicon from titanium silicon carbide—the most common MAX phase. Liters of colloidal solutions of delaminated Ti₃SiC₂‐derived MXene (0.5–1.3 mg mL^?1) were produced and processed into flexible and electrically conductive films, which show higher oxidation resistance than MXene synthesized from Ti₃AlC₂. This new synthesis method greatly widens the range of precursors for MXene synthesis.     

MXenes的制备、结构调控及电化学储能应用

MXenes因其独特的二维层状结构、较高的比表面积、优异的导电性、良好的表面亲水性和化学稳定性,受到国内外研究者的广泛关注。近年来,研究者普遍采用含氟刻蚀剂(HF与LiF-HCl等)选择性刻蚀MAX相中的A位元素,制备带有丰富表面基团的多层MXenes材料。由于含氟刻蚀剂的污染问题,当前采用更为绿色环保的无氟刻蚀剂(NaOH与ZnCl₂等)刻蚀MAX相的研究报道越来越多。MXenes的性能与其结构密切相关,不同制备方法对MXenes的层间距和表面基团的影响很大,进而也影响其性能。基于此,本文总结对比了文献中MXenes的制备方法,概述了MXenes层间距和表面基团的调控方法,同时介绍了MXenes在电化学储能方面的应用,最后对今后MXenes研究所面临的挑战和发展方向进行了展望。     

Bifunctional oxygen electrocatalysts for rechargeable zinc−air battery based on MXene and beyond

Oxygen electrocatalysts are of great importance for the air electrode in zinc–air batteries (ZABs). Owing to large surface area, high electrical conductivity and ease of modification, two-dimensional (2D) materials have been widely studied as oxygen electrocatalysts for the rechargable ZABs. The elaborately modified 2D materials-based electrocatalysts, usually exhibit excellent performance toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which have attracted extensive interests of worldwide researchers. Given the rapid development of bifunctional electrocatalysts toward ORR and OER, the latest progress of non-noble electrocatalysts based on layered double hydroxides (LDHs), graphene, and MXenes are intensively reviewed. The discussion ranges from fundamental structure, synthesis, electrocatalytic performance of these catalysts, as well as their applications in the rechargeable ZABs. Finally, the challenges and outlook are provided for further advancing the commercialization of rechargeable ZABs.     

气敏新材料MXenes在呼出气体传感器中的应用

电子鼻结合人工智能对呼出气进行检测、分析和识别已成为非侵入性医疗检测领域的研究热点.然而,目前已报道的气体传感材料尚不能同时满足高灵敏度、高选择性和稳定的室温检测,阻碍了气体传感器在医疗健康领域的应用及发展,寻找合适的传感材料具有重要的意义和挑战.新型二维层状纳米材料MXenes具有种类多、比表面积大、导电性能强、表面...     

A First-Principles Study on the Vibrational and Electronic Properties of Zr-C MXenes

Within the framework of density functional theory calculations,the structural,vibrational,and electronic properties of Zr_(n )C_(n-1)(n=2,3,and 4)and their functionalized MXenes have been investigated.We find that the most stable configurations for Zr-C MXene are the ones that the terminal groups F,O,and OH locate on the common hollow site of the superficial Zr layer and its adjacent C layer.F and OH-terminated Zr_3C_(2 )and Zr_4C_(3 )have small imaginary acoustic phonon branches aroundΓpoint while the others have no negative phonon modes.The pristine MXenes(Zr_2C,Zr_3C_(2 )and Zr_4C_3)are all metallic with large DOS contributed by the Zr atom at the Fermi energy.When functionalized by F,O and OH,new hybridization states appear and the DOS at the Fermi level are reduced.Moreover,we find that their metallic characteristic increases with an increase in n.For(Zr_(n )C_(n-1))O_2,Zr_2CO_(2 )is a semiconductor,Zr_3C_2O_(2 )is a semimetal,and Zr_4C_3O_(2 )becomes a metal.     

Gas-surface interactions on two-dimensional crystals

Two-dimensional (2D) crystals have developed into a popular mainstream research topic which is interesting for basic research and many applications. Gas-surface interactions, as reviewed here, are important for catalysis including noble metal-free catalysts, materials science, and surface science as well as environmental and energy technologies. Basic science concerns fundamental differences of 2D crystals and bulk materials as well as e.g. how the substrate of epitaxial 2D crystals affects their surface properties.Most of the attention so far obtained (gas-phase) water adsorption which always was an evergreen in surface science. However, studies about small inorganic/organic molecule adsorption (CO, CO₂, NO_x, O₂, H, rare gases, H₂S, SO₂, alkanes, benzene, alcohols, thiophene, etc.) and surface reactions on 2D crystals (CO oxidation, ethylene epoxidation, oxygen reduction reaction, SO₂ and H₂SO₃ oxidation) started to appear in the literature as well. This review describes all of these probe molecules, but focuses on experimental and theoretical surface science model studies usually conducted at ultra-high vacuum (UHV).The review focusses on graphene and functionalized graphene (graphene oxide, N-graphene, etc.) since the bulk of the literature deals with that system. However, included in fair detail are also many other 2D crystals such as silicatene, zeolite films (doped silicatene), metal dichalcogenides (such as MoS₂, WS₂), boron nitride, MXenes, germanene, silicene, TiO₂, graphane, graphone, and portlandene.As a prototypical example, in recent projects, the wetting properties of e.g. graphene for water were controversially discussed. Therefore, a long chapter is devoted to water on graphene. That dispute was originally based on contact angle measurements at ambient pressure. In the meanwhile detailed surface science works including theoretical modelling are available. Literature on other carboneous surfaces such as HOPG (see list of acronyms) will be considered as a reference. Related works are also visible for other inorganic 2D crystals such as silicatene, i.e., 2D-SiO₂, or 2D-MoS₂ as well as functionalized 2D crystals (i.e. graphene oxide, N-doped graphene, graphane, etc.). Hydrophobic systems also are interesting for applications.Although included in this review, but not described in very detail are electro chemistry studies, projects in the liquid phase, photo-chemistry, high pressure catalysis, and pure engineering studies (membranes, separation, fuel cells). However, in comparison with 2D crystals and to perhaps motivate related UHV surface chemistry projects in the future many of these projects were included to some extent.As a broader objective, this review summarizes the currently available knowledge needed to extend the use of 2D materials beyond the utilization of their remarkable electronic and mechanical properties.     

Two-dimensional hybrid nanomaterials derived from MXenes(Ti_3C_2T_x)as advanced energy storage and conversion applications

The development of two-dimensional hybrid nanomaterial derived from MXenes as high performance electrode material is the key component for the advanced ene rgy storage and conversion systems.In the past decades,MXene derived nanomaterials have attracted greatly interest in scientific activity and potential applications because of their unique synergistic properties such as high thermal stability,excellent electrical conductivity,large surface area,easy to handle and outstanding electro and photo chemical properties.This review is focused on the synthesis of hybrid nanomaterials from MXene(Ti_3C_2T_x) for renewable energy conversion and storage application including hydrogen evolution reaction,supercapacitor,lithium-ion batteries and photocatalysis.Finally,we also summarized the prospect and opportunities of novel two-dimensional hybrid nanomaterials derived MXene(Ti_3C_2T_x) fo r futuristic sustainable energy technology.