Wang Xiaohui, Research Group of High Performance Ceramics, Institute of Metal Research, Chinese Academy of Sciences, has made new progress in Raman spectroscopy to identify surface functional groups of two-dimensional carbide MXene. The Raman peak is identified by in-situ measurement of Raman spectroscopy combined with computational simulation (castep module), and the root cause of MXene high capacitance is clarified. The research results are published on ACS Nano. (ACS Nano 2016, 10, 11344−11350)
First principle calculation combined with in situ electrochemical Raman spectroscopy reveals the origin of MXene tantalum capacitor
In recent years, with the continuous research and understanding of graphene, people have gradually realized the great potential of two-dimensional materials in basic and applied research, which has opened the door to discover more two-dimensional materials. MXene is a novel transition metal carbon/nitride two-dimensional crystal with a structure similar to graphene. The chemical formula is Mn+1XnTx, where n = 1, 2, 3, M is an early transition metal element, and X is carbon or nitrogen. The element, T, is a functional group such as -OH, -O or -F carried on the surface. This type of material can be obtained by hydrofluoric acid stripping layered ceramic material MAX phase, which has excellent mechanical, electronic, magnetic and other properties, especially in the application of electrochemical supercapacitor.
Many literatures have reported the excellent performance of MXene in supercapacitors prepared with H2SO4 aqueous solution as electrolyte, but they have not clearly stated why H2SO4 was chosen as the electrolyte. Recently, the research team led by researcher Wang Xiaohui of the Institute of Metal Research of the Chinese Academy of Sciences revealed the essence of ultra-high capacitance in the H2SO4 electrolyte by MXene represented by Ti3C2Tx by in situ electrochemical Raman characterization. The team demonstrated the effects of different functional groups on the stability and bonding properties of MXene through the previous lattice dynamics study (CASTEP module). It was found that the Raman spectrum of Ti3C2Tx is heavily dependent on the type of functional groups, which can be identified by Raman spectroscopy. Type of functional group (Phys. Chem. Chem. Phys. 17, 9997−10003, 2015). On the basis of this, combined with the advantages of Raman spectroscopy fast, non-destructive and non-contact, the Raman spectral changes of Ti3C2Tx MXene in different electrolytes (H2SO4, (NH4)2SO4, MgSO4) were studied. The change in the H2SO4 electrolyte is obvious, and there is almost no change in the other two electrolytes. By comparing the Raman peaks, it is found that MXene realizes the transition from Ti3C2(OH)2 to Ti3C2O(OH) in H2SO4. This transition is caused by the presence of hydrogen ions, which is also indicated in H2SO4. The Ti3C2Tx stores charge in this tantalum-capacitance behavior in which a redox reaction occurs, thereby obtaining a relatively high capacitance. This also opens up new research ideas for MXene's future research on capacitors. This research was published on ACS nano (ACS Nano, 10, 11344−11350, 2016).
In addition, as an electrode material, good electrical conductivity is also a prerequisite for achieving high performance. The energy band structure and Fermi surface of the multilayer MXene stack were calculated by the first principle method, and the anisotropy of the electronic conductance was predicted. The intrinsic conductive properties were obtained by measuring the single particle MXene in situ, and the conductive properties were confirmed. Anisotropic (Sci. Rep. 5, 16329, 2015). This conductive anisotropic accordion structure may also have potential applications in the sensor field.
Wang Xiaohui, Research Group of High Performance Ceramics, Institute of Metal Research, Chinese Academy of Sciences, has long been committed to layered nanoceramic materials and electrochemical energy storage materials. The research field involves ternary layered MAX phase processable conductive ceramics, two-dimensional MXene and lithium ion battery cathode material LiFePO4. Recent work of the group is also: Nano Letters (16, 795−799, 2016), Phys. Chem. Chem. Phys. (18, 20256−20260, 2016), ChemNanoMat (3, 292−297, 2017).
The research team relies on the National (Joint) Laboratory of Materials Science in Shenyang, and welcomes undergraduates, postgraduates, and postdocs with backgrounds in chemistry, physics, and materials. Questionnaire homepage: http://
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