Self-templated transformation of MOFs into layered double hydroxide nanoarrays with selectively formed Co9S8 for high-performance asymmetric supercapacitors

Abstract

Metal-organic frameworks (MOFs) with tunable pore size, stable porous architectures and large specific surface areas have been widely used as precursors for supercapacitor electrode materials. Herein, MOF-derived hollow nickel cobalt layered double hydroxide (NiCo-LDH) nanoarrays embedded with selectively formed Co9S8 nanoparticles on flexible carbon fibers (CC@NiCo-LDH/Co9S8) are reported. The 2D hollow NiCo-LDH framework from self-templated transformation of MOFs enhances the flow efficiency of ions at interlayers to further reduce the resistance of ion transportation. Significantly, the embedded Co9S8 nanoparticles from selective sulfurization of Co exhibit rich active sites and intimate contact of LDH/Co9S8, which effectively improves the electrochemical properties of CC@NiCo-LDH/Co9S8 hybrids, such as electrical conductivity, capacity performance and structural stability. Due to synergistic interaction of NiCo-LDH nanosheets and embedded Co9S8 nanoparticles, the as-prepared CC@NiCo-LDH/Co9S8 electrode material exhibits an ultrahigh capacitance of 2438 F g−1 at 5 A g−1. Furthermore, the as-assembled asymmetric supercapacitor (ASC) device of CC@NiCo-LDH/Co9S8//activated carbon (AC) achieves a maximum energy density of 38.0 Wh kg−1 at 800.0 W kg−1 and outstanding cycling stability with 93.1％ retention of the initial capacitance after 5000 cycles.