【Research Background】

As a material for the development of two-dimensional layered structures in recent years, transition metal carbon/nitride (MXene) has many advantages, such as ultra-high conductivity, controlled layer structure, small band gap and oxidation activity. The functionalized surface, etc., has attracted a lot of attention from researchers as one of the most promising energy storage materials. MXene‘s synthesis methods, structural design and surface chemical reactions directly affect its electrochemical performance. Recently, Professor Zhang Wenkui of Zhejiang University of Technology published a review article on the famous international energy journal ChemSusChem: Two-Dimensional MXene-Based Energy Storage Materials: Interfacial Structure Design and Functionalization. In this review, the interface structure design and functionalization of MXene and MXene energy storage materials, as well as the structural characteristics and surface chemical reaction mechanism, are systematically summarized. In addition, the effects of structural properties on interface properties, functional groups, and interlayer spacing on energy storage performance are also detailed. Finally, it provides future research directions for the great scientific and technical challenges faced by advanced MXene energy storage materials.



[Graphic introduction]

Figure 1 MXenes used in the field of energy storage and conversion, the typical synthesis method, structural design and functional processing.

Figure 2 Etching mechanism diagram of hydrofluoric acid.

Figure 3 Summary of structural design and functional processing of MXene and MXene energy storage materials.

Figure 4 a) Sample preparation flow chart GITT test chart for representative CTAB-Sn(VI)@Ti3C2Tx; b) XRD and c) different surfactant layer spacing at different processing temperatures. d) the molecular structure of CTAB, e) the possible location of CTA+ between the MXene layers.

Figure 5 a) PVP-Sn(VI)@Ti3C2; b) CTAB-Sn(VI)@Ti3C2; c) CT-Sn(II)@Ti3C2 Microstructure and electrochemical properties of three MXene materials.

Figure 6 a) Preparation of porous MXene/CNT electrode; b) SEM image of Ti3C2Tx/CNT-SA; c) Non-diffusion control process of Ti3C2Tx/CNT-SA at a scan rate of 0.1 mV s-1 (k1v); The ratio of volumetric capacity to mass ratio capacity; e) diffusion and transfer of Na+ and electrons in MXene/CNT-SA porous electrodes.

[summary and outlook]

As a novel energy storage material, the electrochemical properties of MXene and MXene based electrode materials depend mainly on the structure and interface properties. Therefore, the relationship between interface structure design and electrochemical performance is discussed in detail. The structure and interface design mainly include the following three ways: (1) enlargement layer spacing; (2) optimization of surface functional groups; (3) modification of functional complexes. Larger layer spacing, low levels of -F-based functional groups and high levels of -O-based functional groups promote energy storage and enhance electrochemical performance. In general, both the control of surface functional groups and the modification of functional complexes are often accompanied by an increase in interlayer spacing.

Despite the great application prospects in the field of energy storage, the research on MXene and MXene base electrode materials is still in its infancy, and there is still a long way to go to meet the requirements of actual mass production in the future. Rationalized interface structure design and functionalization of MXene-based materials under green, efficient, and controlled synthesis conditions remains a significant challenge. For future research, this paper believes that the research should focus on the following aspects: (1) The exploration of high-quality MXene materials with large-scale sheets with nano-scale defects in mild and safe etching conditions requires consideration of low cost. With factors such as high output, this has far-reaching implications for industrial production. (2) The interactions and functions of MXene‘s functional groups (such as -O, -OH and -F), as well as their effects on electrochemical performance, are still in the cognitive stage and require in-depth systematic research. (3) The chemical and thermal stability of MXene may have a significant impact on its energy storage behavior, and further research is needed.

Literature link:

http://dx.doi.org/10.1002/cssc.201902537

Source: WeChat public number  MXene Frontier