【Job description】

As one of the ideal materials in the field of energy storage devices, MXene has received extensive attention. However, like other two-dimensional materials, MXene also faces the problem of self-stacking during the preparation and application process, which results in the reduction of the electrochemically active surface. At the same time, the wetting of the electrolyte in the electrode and the ion transmission will be affected. In order to overcome the problem of self-stacking of nanosheets and at the same time improve the in-plane ion conductivity, Frédéric Favier from Université Paul Sabatier first used MgO nanoparticles as a hard template to successfully prepare expanded MXene (EM) electrodes, compared to the original MXene nanosheet , EM electrode exhibits good electrochemical performance.

At the same time, the researchers also used urea as a molecular template and obtained Ti3C2Tx-MXene foam (MF) through the subsequent heat treatment process. Similarly, this unique porous structure overcomes the shortcomings brought by self-stacking and exhibits good electrical performance. Chemical properties. As a supercapacitor electrode material, MF has a very high capacitance, especially at high magnification, it still has good performance. The work was published in the top energy journal Nano Energy with the title "Modifications of MXene layers for supercapacitors".

【Graphic introduction】

Figure 1. Schematic diagram of different MXene sample preparations: the top is MXene film preparation; the middle is MgO auxiliary preparation EM; the bottom is urea molecular template preparation MF.

Figure 2. XRD patterns of different samples: (a) Ti3AlC2 MAX phase, (b) MXene, (c) EM, (d) MF.

Figure 3. SEM photos of different samples: (a) Ti3AlC2 MAX phase, (b) MXene, (cd) EM, (ef) MF.

Figure 4. SEM photographs of the surface morphology of (a) MXene film and (bd) MF.

Figure 5. Electrochemical performance characterization of electrode materials without binder when using 1M KOH as electrolyte in the three-electrode system: (a) Comparison of CV curves of different samples at 5 mV s-1 scan rate; (b) MF The CV curve of the electrode at different scan speeds; (c) the comparison of the specific capacitance of each comparative sample with the current density; (d) the current density of 5 A g-1 and 5000 cycles, the capacity of the different samples remains contrasted.

Figure 6. Schematic diagram of ion transmission in the electrode when different comparative samples are used as electrodes.

Figure 7. Electrochemical test of MF // MF symmetric capacitors: (a) CV curve at different sweep speeds; (b) Cycling performance test at a current density of 5 A g-1

Figure 8. Electrochemical test of MF // MnO2 asymmetric capacitors: (a) CV curve at different sweep rates; (b) constant current charge and discharge test at different current densities; (c) specific energy, energy density with power Relationship diagram; (d) Cycle retention rate.

【Work Summary】

In this work, the expanded MXene and MXene cellular materials were prepared by the hard template method and the hole-making method, respectively, so as to solve the self-stacking problem faced by MXene as a two-dimensional material. At the same time, in the 1M KOH electrolyte system, the electrochemical properties of the expanded MXene and MXene cell materials are greatly improved compared to the original MXene material.

This benefits from the increased electrochemically active surface by overcoming self-stacking and good ion transport capabilities. In addition, both MF // MF symmetric capacitors and MF // MnO2 asymmetric capacitors exhibit excellent performance. This work provides a good idea for the application of MXene nanosheet energy storage device electrodes.

【references】

Y. Zhu, K. Rajoua, S. Le Vot, O. Fontaine, P. Simon, Fréé. Favier, Modifications of MXene layers for supercapacitors, Nano Energy (2020), doi: https://doi.org/10.1016/ j.nanoen.2020.104734.

Source of information: DT New Materials