Zeolitic imidazolate framework-derived Co3S4@Co(OH)2 nanoarrays as self-supported electrodes for asymmetric supercapacitors

Rational design of high performance self-supported core-shell nanoarrays for asymmetric supercapacitors (ASCs) is highly desired yet challenging. Herein, starting from a 2D Co-based zeolitic imidazolate framework (Co-ZIF-L), Co3S4@Co(OH)(2) nanosheet arrays (NSAs) are prepared on Ni foam through a facile two-step hydrothermal synthesis and used as a self-supported electrode for ASCs. In such a unique architecture, crosslinked ultrathin Co(OH)(2) nanoflakes are anchored on Co-ZIF-L-derived Co3S4 nanosheets with strong adhesion. The Co3S4@Co(OH)(2) NSAs exhibit a high specific capacitance of 2974.0 F g(-1) (1 A g(-1)) with superior rate capacity (76.0% at 10 A g(-1)), due to multiple advantages offered by the hierarchical core-shell structure, such as high electrical conductivity, efficient charge transport, highly exposed active sites, and the synergistic effect between Co3S4 and Co(OH)(2). Moreover, an ASC based on Co3S4@Co(OH)(2) NSAs and activated carbon (AC) can exhibit a high energy density of 41.0 W h kg(-1) at a high power density of 1125.9 W kg(-1) with decent cycling stability (capacitance retention of 75.0% after 10 000 cycles). Two connected ASCs can light up a red light-emitting diode (LED) for more than 3 min, further demonstrating the potential of Co3S4@Co(OH)(2) NSAs in practical electrochemical energy storage. The strategy developed here can be simply extended to the fabrication of other core-shell structures with versatile functions.