Since their discovery in 2011, the number of 2D transition metal carbides and nitrides (MXenes) has steadily increased. Currently more than 40 MXene compositions exist. The ultimate number is far greater and in time they may develop into the largest family of 2D materials known. MXenes’ unique properties, such as their metal‐like electrical conductivity reaching ≈20 000 S cm−1, render them quite useful in a large number of applications, including energy storage, optoelectronic, biomedical, communications, and environmental. The number of MXene papers and patents published has been growing quickly. The first MXene generation is synthesized using selective etching of metal layers from the MAX phases, layered transition metal carbides and carbonitrides using hydrofluoric acid. Since then, multiple synthesis approaches have been developed, including selective etching in a mixture of fluoride salts and various acids, non‐aqueous etchants, halogens, and molten salts, allowing for the synthesis of new MXenes with better control over their surface chemistries. Herein, a brief historical overview of the first 10 years of MXene research and a perspective on their synthesis and future development are provided. The fact that their production is readily scalable in aqueous environments, with high yields bodes well for their commercialization.
This content will become publicly available on April 11, 2024
- Award ID(s):
- 2101001
- Publication Date:
- NSF-PAR ID:
- 10408788
- Journal Name:
- Nanotechnology
- Volume:
- 34
- Issue:
- 25
- Page Range or eLocation-ID:
- 252001
- ISSN:
- 0957-4484
- Sponsoring Org:
- National Science Foundation
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MXenes are a rapidly growing class of 2D transition metal carbides and nitrides, finding applications in fields ranging from energy storage to electromagnetic interference shielding and transparent conductive coatings. However, while more than 20 carbide MXenes have already been synthesized, Ti 4 N 3 and Ti 2 N are the only nitride MXenes reported so far. Here by ammoniation of Mo 2 CT x and V 2 CT x MXenes at 600 °C, we report on their transformation to 2D metal nitrides. Carbon atoms in the precursor MXenes are replaced with N atoms, resulting from the decomposition of ammonia molecules. The crystal structures of the resulting Mo 2 N and V 2 N were determined with transmission electron microscopy and X-ray pair distribution function analysis. Our results indicate that Mo 2 N retains the MXene structure and V 2 C transforms to a mixed layered structure of trigonal V 2 N and cubic VN. Temperature-dependent resistivity measurements of the nitrides reveal that they exhibit metallic conductivity, as opposed to semiconductor-like behavior of their parent carbides. As important, room-temperature electrical conductivity values of Mo 2 N and V 2 N are three and one order of magnitude larger than those ofmore »
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Abstract MXenes are 2D materials with relatively high surface areas, high electrical conductivities, functional transition metal surfaces, tunable surface chemistries, and solution processability. Due to these properties, 2D MXenes have attracted widespread attention as electrode materials for energy storage devices, including electrochemical capacitors, with high power and energy densities. However, many studies have shown that the electrochemical performance of MXene electrodes is considerably affected by their structure and morphology. These properties are, for the most part, controlled by the method used for the assembly of 2D MXene flakes and the electrode fabrication methods. A successful electrode assembly and fabrication method should address several challenges, such as the restacking of 2D flakes, to achieve electrode structures and morphologies that deliver high ionic transport properties, electrical conductivity, and mechanical stability. This review aims to provide insight into the current state‐of‐the‐art assembly and fabrication methods used to design and fabricate high performance electrodes based on MXenes. The major challenges to be addressed and possible future directions in the fabrication of MXene electrodes for practical energy storage applications are highlighted.
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m H2SO4electrolyte as follows: V‐Ti4N3Tx> Cr‐Ti4N3Tx> Mo‐Ti4N3Tx> Mn‐Ti4N3Tx> pristine Ti4N3Txwith overpotentials as low as 330 mV at −10 mA cm−2with a charge‐transfer resistance of 70 Ω. Scanning electrochemical microscopy (SECM) reveals the electrochemical activity of individual MXene flakes. The SECM data corroborate the bulk HER activity trend for M‐Ti4N3Txas well as provide the first experimental evidence that HER results from catalysis on the MXene basal plane. These electrocatalytic results demonstrate a new pathway to tune the electrochemical properties of MXenes for water splitting and related electrochemical applications.
