Review of MXenes research progress in 2020

In 2020, which is destined to be extraordinary, the research of MXenes has achieved leapfrog development. According to the data of Web of Science, the number of research papers related to MXenes has reached 1,458 in 2020. Considering the impact of the COVID-19 epidemic on scientific research Compared with the number of 941 papers published in 2019, it is not easy to achieve such results. Today, let us lead everyone to take stock of representative work in the 2020 MXenes study.

•Top Science/Nature

The Argonne National Laboratory and Professor Dmitri V. Talapin from the University of Chicago published a research paper titled Covalent surface modifications and superconductivity of two-dimensional metal carbide MXenes in the top international academic journal Science. It is a general strategy to perform substitution and elimination reactions to control the functional groups on the surface of MXene. Successfully synthesized MXenes with O, NH, S, Cl, Se, Br and Te surface functional groups, and MXenes without any surface functional groups. The prepared MXene has some unique structures and electronic properties. Surface functional groups can control the distance between atoms in the MXene lattice. Compared with the TiC lattice, Tin+1Cn (n=1, 2) with Te2-ligand will produce a huge planar extended lattice (>18%).

Professor Yang Shubins research group from Beijing University of Aeronautics and Astronautics and Professor Pulickel M. Ajayan from Rice University in the United States published a research paper titled: Conversion of non-van der Waals solids to 2D transition-metal chalcogenides in the top international academic journal Nature. A topological transformation method is used to convert van der Waals solid into 2D van der Waals transition metal chalcogenide with 2H/1T phase. This conversion is achieved by exposing non-van der Waals solids to chalcogen vapor, which can be controlled by controlling the entropy and vapor pressure of the reaction product. Heteroatom-substituted transition metal chalcogenides (such as yttrium and phosphorus) can also be prepared in this way. Therefore, the phase-selective 2D transition metal chalcogenides obtained by this general method can be used at high temperatures (1373 Kelvin) has good stability, and at the same time it can also realize the mass production of single-layer materials, which has far-reaching significance for the development of single-layer two-dimensional materials.

Professor Huang Qing from the Ningbo Institute of Materials, Chinese Academy of Sciences, Professor Patrice Simon from the University of Toulouse in France, and Professor Lin Zifeng from Sichuan University published in the top international academic journal Nature Materials on the topic: A general Lewis acidic etching route for preparing MXenes with enhanced electrochemical performance in non-aqueous electrolyte paper. Quite different from the traditional method, the paper proposes a method for preparing MXenes by selective etching of A in the MAX phase of non-traditional A elements using Lewis acid molten salt, and has been verified accordingly. When Ti3C2MXene etched by this method is used for lithium storage, it has a reversible capacity of 738C g-1 (205 mAh g-1) and a high coulombic efficiency.

• The internationally renowned academic journal Advanced Functional Materials even launched seven MXenes review articles in different research fields at the same time in one day. Let us review some representative review articles together.

The structure evolution and electrochemical reaction mechanism of MXene-based electrodes during different cycles need to be seeed. In-situ characterization, such as in-situ SEM, in-situ TEM, in-situ electrochemical Raman spectroscopy, in-situ XPS, etc. will greatly help us to fully understand the changes in the composition and structure of MXene-based electrodes, such as surface functional groups and electrolysis The dynamic and dynamic formation process of the interface between the liquid and the SEI film.

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Professor Feng Jinkui of Shandong University published a review article titled: Recent Advances of Emerging 2D MXene for Stable and Dendrite-Free Metal Anodes in the international high-level academic journal Advanced Functional Materials, summarizing the application of MXene materials in stable non-dendritic metal anodes Progress and prospects for future research directions: i) increase the diversity of synthesis methods for MXenes used in metal anodes; ii) design more MXene-based host structures for metal anodes; iii) improve MXene and liquid electrolyte; iv) Explore the application of MXene in more metal anodes; v) Design a variety of flexible MXene/metal composite anodes; vi) evaluate practical application capabilities; vii) recycling technology; viii) combine with advanced technologies.

Professor Joselito M. Razal from Deakin University, Professor Yury Gogotsi from Drexel University and Professor Genevieve Dion published in the internationally renowned academic journal Advanced Functional Materials on the topic: MXene-Based Fibers, Yarns, and Fabrics for Wearable Energy Storage Devices A review article summarizing the technology and research progress of preparing MXene-based textile electrodes, as well as the development prospects of MXene-based fibers with controllable mechanical, electronic and electrochemical properties: i) Size: expand the fiber electrode from several centimeters to several meters; ii) Improve the mechanical properties of the fiber electrode to withstand the mechanical stress that the fiber will encounter in the preparation of textiles. Once these needs are met, the advantages of industrial textiles will double.

Professor Majid Beidaghi of Auburn University in the United States published a review article titled A Review of the Effects of Electrode Fabrication and Assembly Processes on the Structure and Electrochemical Performance of 2D MXenes in the internationally renowned academic journal Advanced Functional Materials, summarizing the advantages of MXene-based electrodes Research progress in assembly methods, such as combining MXenes with other electrochemically active nanomaterials, has proven to be an effective way to prepare high-performance electrode materials. For example, MXene and 2D TMO heterojunction can combine the high specific capacitance of TMO and the high conductivity of MXenes. At the same time, the two can effectively prevent aggregation and re-stacking, which will improve the capacitance and rate performance. However, in some cases, the synthesis of heterojunctions or composite electrodes will introduce additional defects.

Since most MXene synthesis methods produce aqueous dispersions, wet chemical methods are often used to synthesize MXene-based composite materials. Among them, stacking is a common problem of synthetic composite materials. The use of suitable surfactants may be a practical solution to this problem. The morphology of composite materials can be prepared and designed by using electrostatic adsorption. However, in this type of process, how to remove the remaining surfactant is a big problem.

When MXene composite is used as the electrode material of the battery, MXene is mainly used as a conductive framework to support higher electrochemically active materials. It is designed into a stable structure and can withstand the volume expansion of nanoparticles during the process of embedding and de-embedding. It is a very important consideration. The main challenge is to control the pore size and morphology of the composite material to ensure the uniform distribution of nanoparticles on the surface of MXene.

Professor Wu Zhongshuai from the Dalian Institute of Physics, Chinese Academy of Sciences published a research progress report titled Recent Advances and Promise of MXene-Based Nanostructures for High-Performance Metal Ion Batteries in the internationally renowned academic journal Advanced Functional Materials, systematically summarizing the MXenes-based nanomaterials Research progress in batteries has emphasized that MXenes can be used as active materials, as well as conductive substrates and even as current collectors. In addition, the method of loading, coating and forming a sandwich structure of MXene-based composites in different dimensions (0D, 1D and 2D) was elaborated, and the prospects for future research directions were put forward.

Professor Jong-Min Lee from Nanyang Technological University in Singapore and Professor Xiao Xu from University of Electronic Science and Technology of Singapore published a review article titled Transition metal nitrides for electrochemical energy applications in the top international review journal Chem Soc Rev, summarizing the transition metal nitride-based nano The latest research progress of materials mainly focuses on geometric structure design, electronic structure engineering, and applications in electrochemical energy conversion and storage, including electrocatalysis, supercapacitors and rechargeable batteries. Finally, the future research directions of transition metal nitride-based nanomaterials are prospected:

For energy storage applications: 1) The stable voltage window of supercapacitors is not only determined by the inherent properties of transition metal nitrides, but also affected by the electrolyte used. Compared with the most commonly used aqueous electrolytes, ionic liquids or Organic electrolytes can provide higher output voltages, thereby producing higher energy density; 2) Transition metal nitrides are currently the most widely used in lithium-ion batteries, but due to limited lithium resources, they cannot reach the actual high The need for scale power usage. The application research of transition metal nitrides in sodium-potassium ion batteries with more abundant reserves and cheaper prices is still in the initial stage. 3) The high conductivity and catalytic activity of transition metal nitrides can promote the redox reaction kinetics when capturing polysulfide lithium and dissolving Li2S2/Li2S. However, the detailed catalytic mechanism is not completely clear at present and needs to be explored more deeply. 4) From the perspective of chemical composition, the current research is mainly focused on the composite of transition metal nitrides, inorganics, carbon, etc., almost no organics are introduced. Taking into account the diversity and versatility of organics, compounding transition metal nitrides with organics may inspire new ideas.

Professor Husam N. Alshareef from King Abdullah University of Science and Technology in Saudi Arabia published a review article titled MXene Printing and Patterned Coating for Device Applications in the top international academic journal Advanced Materials. The review systematically summarized MXenes through printing/coating methods. And applications in different fields, and prospects for the future development direction of graphical MXenes. In the current early stage of development, only a few printing and coating methods are used to deposit and coat MXenes materials. Although some devices have been reported to have outstanding performance, more research focus should be placed on the transition from laboratory research to large-scale applications in practical applications. Ultimately, researchers need to conduct detailed studies on optimizing the inks used in the printing/coating process. Facing the future, the improvement of the ability to print fine structures will greatly improve the performance of the device, lower production costs and the ease of integration, thereby promoting the miniaturization of MXene-based devices.

Professor Maowen Xu from Southwest University in Advanced Energy MaterThe title published on ials: MXenes for Non-Lithium-Ion (Na, K, Ca, Mg, and Al)Batteries and Supercapacitors review article, systematically summarized the synthesis, structure, performance and performance of MXene in non-lithium ion energy storage technology Application, and forecast the future development direction:

i) Find out the limiting factors and shortcomings of the large-scale preparation of MAX phase materials and MXene materials, reduce synthesis costs, explore key factors affecting the synthesis process, and explore novel environmentally friendly etching methods.

ii) Explore the reaction mechanism between MXene nanosheets and different solvents, and improve the stability of MXene dispersion in water and organic solvents, such as adding antioxidants and other strategies.

iii) Study the effect of MXene surface chemistry on performance.

iv) Deepen the calculation ability of theoretical simulation, and design more potential MAX and MXene phase materials through theoretical simulation.

v) Development and application of MXene-based solid-state secondary batteries.

vi) Through reasonable structural design, make full use of the structural advantages of MXene to increase its volume capacity

vii) Develop flexible and transparent MXene film for future wearable electronic devices.

viii) MXene-based hybrid supercapacitors have both high power density and energy density, and have high practical value.

Professor Jilei Liu from Hunan University published a review article in the internationally renowned academic journal Advanced Energy Materials: The Role of Cation Vacancies in Electrode Materials for Enhanced Electrochemical Energy Storage: Synthesis, Advanced Characterization and Fundamentals, systematically summarizing the electrochemistry of cation vacancies The latest developments in energy storage materials, including corresponding synthesis methods and characterization techniques, and positioning their roles in practical applications from the perspective of chemical materials, key challenges and opportunities for future development, especially transition metal oxides with cation defects and emerging The transition metal carbide (MXene). Many effective strategies can be used to promote the formation of cation defects, adjust the concentration of vacancies, including variable valence cation/anion doping, maintain balance in solutions with different pH values, and selectively remove cations in components. Annealing and plasma etching in an atmosphere. The direction of future research is mainly reflected in the following aspects:

i) Quantitative determination of cation vacancies and their spatial distribution, especially in highly disordered nanostructures, is still challenging.

ii) The defect structure is generally metastable. Therefore, cationic defect materials (especially those with large specific surface area and porous nanostructured materials) usually encounter the problem of physical and chemical instability.

iii) In order to accurately understand the role of cation vacancies, we need to exclude other factors that affect the performance of metal oxides/carbides.

iv) Although the presence of cation vacancies leads to an increase in the storage charge capacity and rate, it is still unclear how cation vacancies improve the energy storage performance of metal oxides/carbides.

Professor Andre´ D. Taylor from New York University published a review article titled Layer-by-Layer Assembly of Two-Dimensional Materials: Meticulous Control on the Nanoscale in the internationally renowned academic journal Matter. The layer-by-layer assembly technology provides a unique and universal In this way, the special properties of 2D materials can be displayed on macroscopic devices, and new 2D material-based functional composites can be innovatively designed. The most important thing is that the layer-by-layer assembly technology can achieve the effect of simultaneously controlling the thickness and layered structure of 2D materials, thereby enabling the materials to achieve the best performance advantages in many applications. The unique properties of graphene-based materials, MXenes and TMD, as well as strong ζ-potential and easy dispersion in water make it the best candidate for layer-by-layer assembly technology. The performance of the composite prepared by this assembly technology is greatly improved compared with the corresponding non-layer-by-layer composite composite, which benefits from the control of interface contact and thickness on the nano-scale, which prevents 2D materials The re-stacking problem. Through the layer-by-layer assembly of 2D materials, many possibilities can be used to extend the high-performance materials we know. In principle, it is important to expand the MXene and TMD composite system with composition diversity, and it is also the focus of future research directions. As researchers continue to expand and develop new and unique 2D material families with layered structures, the future prospects for layer-by-layer assembly are very broad.

Professor Song Li from the University of Science and Technology of China and Dr. Shuangming Chen published a review article titled Tuning 2DMXenes by Surface Controlling and Interlayer Engineering: Methods, Properties, and Synchrotron Radiation Characterizations in the internationally renowned academic journal Advanced Functional Materials, which summarized comprehensively and systematically MXenes-based nanomaterials have surface control, interlayer engineering and characterization based on simultaneous X-ray absorption. Although the surface functional groups and interlayer engineering of MXenes have a very important influence on its structure and application, the research on the influence of single functional groups is usually limited to theoretical calculations. Therefore, novel synthesis methods and subsequent processing methods are still needed to prepare MXenes with specific surface functional groups. Researchers need to work harder to achieve selective intercalation through specific intercalating agents to improve performance. On the other hand, the design of MXene-based composite materials with outstanding performance is also crucial to its breakthroughs in various fields. It is worth noting that benefiting from the development of SR light sources and the need for in-depth research on the structure and mechanism of MXenes in the corresponding fields, many other SR-based characterization methods besides XAS are urgently needed to be developed to explore the development of MXenes materials, such as SXRD, SXPS, FTIR and APXPS technology based on XR, etc.

Professor Zhang Han of Shenzhen University published a review article titled MXene/Polymer Membranes: Synthesis, Properties, and Emerging Applications in the internationally renowned academic journal Chemistry of Materials. The review first discussed the synthesis methods and properties of 2D MXenes, which can be used as MXene /Polymer composite membrane precursor. Secondly, the assembly strategy and performance of MXene/Polymer composite membrane are summarized. In addition, the applications of MXene/Polymer composite membranes, such as filtration, electromagnetic shielding, supercapacitors, sensors, etc., are also summarized. The performance of MXene/Polymer composite film has a great relationship with the distribution of MXene nanosheets. According to reports, in the process of synthesizing MXene/Polymer composite membranes, MXene may aggregate, and then produce multi-scale phase separation. Therefore, it is necessary to focus research on improving the dispersibility of MXene nanosheets in the polymer matrix. This can be achieved through proper functionalization of polymer chains to achieve enhanced contact between MXene nanosheets and polymers.

Professor Husam N. Alshareef of King Abdullah University of Science and Technology in Saudi Arabia published a review article titled: MXene hydrogels: fundamentals and applications in the top international review journal Chem Soc Rev, summarizing the different structures of various MXene-based hydrogel systems. And the gelation mechanism and the corresponding driving force. In principle, similar to other hydrogels, the gelation of MXene-based hydrogels includes covalent and non-covalent cross-linking methods; due to the lack of research on basic issues, such as MXene nanosheets and hydrogel systems The mass/charge transfer between other components, the kinetics/thermodynamics of the assembly process, and the mechanism of the interaction between the components; the existing devices based on MXene hydrogels are all artificially prepared and remain in the experiment At the laboratory level, it is difficult to replicate or mass produce. This is also the direction that future researchers need to focus on.

•The 3rd International Transition Metal Carbide (MXenes) Academic Seminar hosted by Researcher Huang Qing and Professor Yury Gogotsi was successfully held in Ningbo Institute of Materials, Chinese Academy of Sciences. The development direction of MXene in the next ten years is prospected.

(PS: The high-definition original picture can be obtained by entering "MXene Challenge" in the background~)

Related literature links:

1.Covalent surfacemodifications and superconductivity of two-dimensional metal carbide MXenes

DOI: 10.1126/science.aba8311

2.Conversion of non-van derWaals solids to 2D transition-metal chalcogenides

https://doi.org/10.1038/s41586-019-1904-x

3. A general Lewis acidicetching route for preparing MXenes with enhanced electrochemical performance innon-aqueous electrolyte

https://doi.org/10.1038/s41563-020-0657-0

4. Interface Chemistry onMXene-Based Materials for Enhanced Energy Storage and Conversion Performance

DOI: 10.1002/adfm.202005190

5. Recent Advances of Emerging 2D MXene for Stable and Dendrite-Free Metal Anodes

https://doi.org/10.1002/adfm.202004613

6.MXene-Based Fibers, Yarns, and Fabrics for Wearable Energy StorageDevices

https://doi.org/10.1002/adfm.202000739

7. A Review of the Effects of Electrode Fabrication and Assembly Processes on the Structure and Electrochemical Performance of 2D MXenes

https://doi.org/10.1002/adfm.202005305

8. Recent Advances and Promise of MXene-Based Nanostructures for High-Performance Metal Ion Batteries

https://doi.org/10.1002/adfm.202000706

9. Transitionmetal nitrides for electrochemical energy applications

DOI: 10.1039/d0cs00415d

10. MXene Printing and Patterned Coating for Device Applications

https://dx.doi.org/10.1021/acs.chemmater.9b04408

11. MXenes for Non-Lithium-Ion (Na, K, Ca, Mg, and Al)Batteries and Supercapacitors

DOI: 10.1002/aenm.202000681

12. The Role of Cation Vacancies in Electrode Materials for Enhanced Electrochemical Energy Storage: Synthesis, Advanced Characterization and Fundamentals

https://doi.org/10.1002/aenm.201903780

13. Layer-by-Layer Assembly of Two-Dimensional Materials: Meticulous Control on the Nanoscale

https://doi.org/10.1016/j.matt.2020.03.012

14.Tuning 2D MXenes bySurface Controlling and Interlayer Engineering: Methods, Properties, andSynchrotron Radiation Characterizations

https://doi.org/10.1002/adfm.202000869

15. MXene/Polymer Membranes: Synthesis, Properties, and Emerging Applications

https://dx.doi.org/10.1021/acs.chemmater.9b04408

16. MXene hydrogels: fundamentals and applications

DOI: 10.1039/d0cs00022a

Source: MXene Frontier

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