Hollow C-LDH/Co9S8 nanocages derived from ZIF-67-C for high- performance asymmetric supercapacitors.

The design of supercapacitor electrode materials greatly depends on the rational construction of nanostructures and the effective combination of different active materials. Due to the poor electrical conductivity and mechanical strength, nickel-cobalt double hydroxide (NiCo-LDH) cannot reach the theoretical high specific capacitance value, while Co9S8 shows many interesting features, such as excellent electrochemical properties, high conductivity, and greatly improved redox reactions. Therefore, we prepared ZIF-67-C derived hollow NiCo-LDH (C-LDH)/Co9S8 nanocages containing two components of Co9S8 and NiCo-LDH through a multistep transformation method. The prepared C-LDH/Co9S8 nanoparticles showed a hollow rhomboid dodecahedron structure, and many NiCo-LDH nanosheets were reasonably distributed on the surface. In the three-electrode test, it can be obtained that its specific capacitance is 1654 F·g-1 when current density is 2 A·g-1 and 82.5% capacitance retention after 5000 cycles. Moreover, asymmetric supercapacitors (ASCs) prepared with C-LDH/Co9S8 as cathode and AC as anode can achieve a large energy density of 47.3 Wh·kg-1 under the condition of high power density of 1505 W·kg-1. After 10,000 cycles, capacitance retention rate is 80.9%, exhibit excellent cycle performance, suggesting the great potential of hollow C-LDH/Co9S8 nanocages in the application of supercapacitors.