Preparation of graphene composite electrode material by electrostatic self-assembly method

MXenes is a new two-dimensional transition metal carbide or carbonitride material. Its chemical formula can be represented by Mn+1XnTx, where M refers to transition metal, X refers to C or N, n is generally 1-3, Tx Refers to the surface group. Because of its high specific surface area, high conductivity and good hydrophilic properties, it is widely used in energy storage fields such as lithium ion batteries, sodium ion batteries, and supercapacitors. Similar to graphene, the aggregation and stacking of MXene nanosheets is inevitable, which seriously affects its electrochemical performance.

Figure 1 MXene/rGO composite material synthesis process diagram.

Recently, Professor Yury Gogotsi of Drexel University and others used positively charged reduced graphene oxide (rGO) and negatively charged titanium carbide MXene nanosheets as raw materials, synthesized by electrostatic self-assembly method MXene/rGO composite material was developed as a supercapacitor electrode material, showing superior electrochemical performance. This result was published in the international journal Adv. Funct. Mater.

Figure 2 (a) CV diagram of MXene and MXene/rGO in 3 M H2SO4 electrolyte with a sweep rate of 20 mV/s; (b) M/G -5% electrode CV diagram at different scanning speeds; (c) The relationship between the peak current of M/G-5% electrode and the scanning rate (2-50 mV/s); (d) M/G- Charge and discharge curves of 5% electrodes at different current densities; (ef)Mass specific capacitance and volume specific capacitance of MXene and MXene/rGO electrodes at different scanning speeds.

Figure 3 (a) CV diagrams of MXene and M/G-5% electrodes in symmetric supercapacitors at different scanning speeds; (b) mass ratio capacitance diagrams; MXene And M/G-5% electrode in a symmetrical supercapacitor (c) mass; (d) volume energy and power density diagram.

M/G-5% (5% is the mass fraction of rGO) composite material exhibits ultra-high conductivity (2261 S/cm) and density (3.1 g/cm^3) and superior Electrochemical performance. Using 3 M H2SO4 electrolyte as the electrolyte, the electrochemical performance of the MXene/rGO electrode was measured using a three-electrode system.

At scanning speed of 2 mV/s, M/G-5% electrode volume specific capacitance is as high as 1040 F/cm^3; at scanning speed of 100 mV/s and 1 V/s, volume specific capacitance It is 777 and 634 F/cm^3, which reflects good rate performance. In order to test the performance of the M/G-5% electrode in practical applications, it was applied to a symmetrical supercapacitor, which showed an ultra-high volumetric specific energy density of 32.6 Wh/L.

The author explained in the article the reason why the MXene/rGO electrode has such good electrochemical performance:

(1) Inserting rGO nanosheets between the MXene layers can not only effectively inhibit MXene Stacking between layers can increase the layer spacing of MXene to form a well-aligned alternate arrangement structure. This is conducive to the rapid diffusion and transportation of electrolyte ions, and improves the electrochemical utilization and rate performance of MXene;

(2) Good electrical conductivity is conducive to rapid ion transfer during charge and discharge, reducing internal impedance ;

(3) The high electrode density is beneficial to increase the volume specific capacitance.