【Research Background】

Due to the increasing global demand for energy, people have begun extensive research on new high-performance energy storage equipment. Supercapacitors, such as electrochemical capacitors (EC), are used as supplemental energy storage devices for batteries in electric vehicles, wearables, and portable electronic devices due to their fast charge / discharge performance, high power density, and excellent cycle life. Wide application. In 2011, MXenes was reported as a new two-dimensional graphene-like material. However, compared to graphene, MXenes is considered to be a promising two-dimensional supercapacitor material due to its metal conductivity and hydrophilicity, which has the advantages of large specific surface area, high electrical conductivity, and good cycle stability. . However, its low specific capacity limits its widespread use.

[Achievement Profile]
Recently, in order to solve this problem, the team of Professor Min Jae Ko of Hanyang University has uniformly deposited NiCo2S4 nano flakes (called MXene-NiCo2S4 @ NF) on the surface of MXene on conductive foam nickel, which is used as a binderless composite in supercapacitor applications. electrode. NiCo2S4 nanosheets increase the surface area of the composite electrode, thereby increasing its specific capacity from 106.34 C g-1 to 596.69 C g-1 at 1 A g-1. Compared with the original MXene, MXene-NiCo2S4 @ NF maintains the high retention rate of the original MXene and shows excellent cycle stability after 3000 cycles, which is 80.4% of the initial specific capacity. Due to the combined advantages of NiCo2S4 (high specific capacity) and MXene (high retention and good cycle stability), the electrochemical performance of the composite electrode for supercapacitors has improved. Using MXene-NiCo2S4 as the positive electrode and activated carbon as the negative electrode, the produced asymmetric solid supercapacitor showed an energy density of 27.24 Wh kg-1 at a power density of 0.48 kW kg-1. The results were published online in the Journal of Industrial and Engineering Chemistry: 3D Hierarchical Transition-Metal Sulfides Deposited on MXene as Binder-Free Electrode for High-Performance Supercapacitors


[Picture and text guide]

Figure 1. Schematic diagram of MXene-NiCo2S4 electrode fabrication process

Figure 2. (a) XRD spectrum of MXene-NiCo2S4 and (b) XPS measurement spectrum; (c, d) nuclear-level spectra of Ni 2p and s2p regions

Figure 3. (a, b) SEM (inner images of (a) and (b) show the inserted MXene) and (c, d) TEM images of the MXene-NiCo2S4 electrode at different magnifications Showing SAED Atlas

Figure 4. (a) GCD curves of 60-MXene-NiCo2S4 @ NF electrodes at different scan rates and CV curves and (b) different current densities d) Cyclic stability of 60-MXene-NiCo2S4 @ NF electrode and 0-MXene-NiCo2S4 @ NF electrode after several cycles at 10 A g-1 and (inside picture) 60-MXene-NiCo2S4 @ NF sample at 3000 SEM image after cycling
Figure 5. (a) Schematic diagram of ASC device (b) CV curve of the device at different scan rates (c) Charge and discharge curve of the device at different current densities (d) Power density and energy comparison chart of ASC device

[Summary of this article]
In this study, a novel 3D MXene-NiCo2S4 nanostructure was prepared as a binderless electrode for chemical capacitors. The proposed structure not only overcomes the low specific capacitance of MXene, but also improves the weak cycle stability and low conductivity of TMS. First, an MXene colloid solution was synthesized and fixed to NF without using a binder, which effectively reduced internal resistance and accelerated charge transfer. Then, the precursor was electrodeposited on the surface of the MXene nanoplate, and sodium sulfide nonahydrate was added thereto, and then vulcanized by a hydrothermal anion exchange reaction. The fabricated MXene-NiCo2S4 electrode exhibits excellent electrochemical performance, high specific capacity (596.69 C g-1 at 1 A g-1), and excellent cycle stability (the original capacity is maintained after 3000 cycles). 80%). The cyclic stability is mainly due to the unique nanostructure of the MXene structure, which not only provides a large surface area, but also withstands volume changes due to applied charges and redox reactions. In addition, the ASC device assembled with MXene-NiCo2S4 as the positive electrode and AC as the negative electrode exhibited a high energy density of 27.2 Wh · kg-1 and a high power density of 0.48 kW · kg-1. The results show that the proposed 3D nanostructure can improve the performance of supercapacitors and other energy storage devices.

Literature link:
https://doi.org/10.1016/j.jiec.2019.10.028