Supercapacitors have attracted much attention due to their high power density, excellent rate performance and long cycle life. The successful manufacture of flexible supercapacitors mainly depends on the design of the device structure and the innovation of flexible electrode materials. MXene has the advantages of large specific surface area, high metal conductivity, and good mechanical properties. It is considered to be a promising electrode material for flexible supercapacitors. In recent years, many methods such as vacuum filtration, spinning or spraying, hydrothermal treatment and ice template assembly have been used to manufacture MXene. Although vacuum filtration, spin coating or spraying can achieve the preparation of flexible MXene films, the preparation process is time-consuming and low in efficiency, which hinders its large-scale production. In addition, the compact structure of these flexible MXene membranes often results in limited electrolyte accessible surface area, resulting in undesirable electrochemical performance. On the contrary, hydrothermal treatment and ice template assembly methods can give MXene a three-dimensional porous structure, which is beneficial to improve its electrochemical performance. However, these MXene structures usually cannot be used as highly flexible electrodes due to unsatisfactory mechanical properties. Therefore, there is an urgent need to develop a strategy to achieve the scalable preparation of flexible MXene films with excellent mechanical properties and a good porous structure.
In view of this, Professor Niu Zhiqiang and Dr. Shuai Wang of Nankai University proposed a synchronous reduction and self-assembly strategy to fabricate flexible MXene films, in which the MXene films were synchronously reduced and self-assembled on the surface of the Zn foil. The self-assembled MXene film shows high conductivity, large specific surface area and excellent mechanical properties, and has broad application prospects in flexible supercapacitor electrode materials.

Article highlights:
1. The self-assembly of MXene film can be expanded by controlling the area of the Zn substrate. By adjusting the pattern of the Zn substrate, an interdigitated MXene pattern can also be obtained through a selective reduction/assembly process. The obtained MXene film has higher conductivity, larger specific surface area and excellent mechanical properties.
2. As a proof of concept, flexible sandwich and micro supercapacitors were designed based on the above-mentioned MXene film electrodes. The sandwich and micro supercapacitors both show stable electrochemical performance under different bending states.

Figure 1 Preparation and characterization

Figure 2 Electrochemical performance of sandwich supercapacitors based on MXene film electrodes

Figure 3 Electrochemical performance of miniature supercapacitors based on MXene film electrodes
Original link:
https://doi.org/10.1002/adfm.202101302