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

Abstract

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.