Nickel-molybdenum metal hydroxide wrapped ZIF-67 for supercapacitor applications

Zeolitic imidazolate frameworks (ZIFs) are hopeful materials for energy storage due to their uniform pores, large specific surface area, and good stability. Particularly, the conductivity of Co-based ZIF-67 is 1000 times higher than that of Zn-based ZIF-8, making cobalt-based ZIF-67 widely studied as an energy storage material. At present, there are few reports on the direct synthesis of hollow-structured ZIF-67. Herein, hollow leaf-like Co-ZIF-67 is directly synthesized in an aqueous solution using a simple and environment-friendly method. Then, nickel‑molybdenum layered double hydroxides (NiMo-LDH) nanosheets were wrapped on the Co-ZIF-67 by a hydrothermal treatment. The resulting [email protected] composite has a specific capacitance of 1734 F g−1 (1 A g−1), and its asymmetric supercapacitor (ASC) provides a high energy density of 97.7 Wh kg−1 at a power density of 800 W kg−1 with excellent rate capability (at a power density of 7887 W kg−1 at 10 A g−1 and an energy density of 65.5 Wh kg−1) and cycling stability (88 % capacitance retention after 5000 cycles). The combination of the favorable features of Co-ZIF-67 and NiMo-LDHs and their synergistic effects, especially the unique three-dimensional interconnected nanostructure contributes to the enhanced properties; thus, the composites show great potential as electrode materials for supercapacitors.