Mo-doped ZIF-67 derived Ni, Co, Mo trimetallic sulfide/ carbon nanotubes for supercapacitors

Abstract

Supercapacitors have the advantages of high power density, rapid charge and discharge rates, and extended cycling stability. However, their energy density and specific capacity are still inadequate to satisfy the current requirements for energy storage in the industry. The current work demonstrates the synthesis of Mo-ZIF-67/CNT composites through mechanical stirring and co-precipitation. After that, Ni, Co and Mo trimetallic sulfide/CNT composites (Ni-Co-Mo-S/CNT) are produced through further ion exchange/etching and vulcanization processes. The material has multiple valence states of three different metal ions, providing a large number of oxidation-reduction sites. The doping of CNT endows it with a unique coral-like structure, which helps to form its huge specific surface area and larger mesopores. Furthermore, the effect of vulcanization temperature on the electrochemical performance of the material is also studied. According to the results, the Ni-Co-Mo-S/CNT-180, which is vulcanized at 180 °C, exhibits the most outstanding electrochemical performance. The electrode exhibits impressive performance with a specific capacitance of 1728.6 F/g at a current density of 1 A/g. It also has good rate capability, maintaining 55.8 % of the specific capacitance when the current density increases tenfold. Finally, the prepared Ni-Co-Mo-S/CNT-180//AC asymmetric supercapacitor generated a high energy density of 43 Wh/kg at a power density of 735 W/kg. After 2000 charge-discharge cycles at a current density of 1 A/g, it maintains a capacity of 76.42 %. This study serves as a reference for researching multi-metal sulfides as electrode materials for high-performance supercapacitors.