Hierarchical porous Co9S8 nanowire arrays derived from zeolitic imidazolate framework on Ni foam for button-type asymmetric supercapacitor

Hierarchical porous Co9S8 nanowire arrays grown on Ni foam with the sacrificial template of zeolitic imidazolate framework (ZIF) are successfully synthesized via multi-step preparation for the supercapacitor. Introducing of ZIF-67 is favorable to the formation of the hierarchical pores and small active powder. It is beneficial to provide large surface area and short diffusion channel, which can reduce volume expansion and ensure architecture stability. ZIF-derived Co9S8 displays the large specific capacitance because of its abundant redox sites and high electrical conductivity. The Co9S8/NF electrode has the outstanding electrochemical properties with the specific capacitance of 369.1 mAh g−1 at 1 A g−1, 75.5% retention at 20 A g−1, respectively. After 5000 cycles the specific capacitance can reach 75% retention at 20 A g−1. Furthermore, a button-type asymmetric supercapacitor (ASC) is assembled with Co9S8/NF as positive electrode and displays the maximum specific energy of 48.2 Wh kg−1 at the specific power of 799.8 W kg−1, excellent cycling life with 77% retention of the initial capacitance after 5000 cycles.