Hierarchical core–shell 2D MOF nanosheet hybrid arrays for high-performance hybrid supercapacitors

Abstract

Two-dimensional (2D) metal–organic frameworks (MOFs) with large surface area, ordered pores and ultrathin thickness have recently emerged as ideal electrode materials for supercapacitors (SCs). However, their straightforward applications are restricted by the drawbacks of self-stacking and unsatisfactory electrical conductivity. Herein, ultrathin Ni-MOF nanosheets have been grafted on zeolite imidazolate framework (ZIF-L)-derived porous Co₃O₄ nanosheets to form hierarchical core–shell Co₃O₄@Ni-MOF 2D nanosheet hybrid arrays. The porous Co₃O₄ “core” acts as a conductive skeleton for anchoring Ni-MOF and provides shortened ion diffusion paths. The Ni-MOF “shell” can expose large active sites. Benefiting from these merits and the synergic effects of the “core and “shell”, the Co₃O₄@Ni-MOF/NF shows a high specific capacity (capacitance) of 225.6 mA h g⁻¹ (1980.7 F g⁻¹) at 1 A g⁻¹ with decent capacitance retention (82.2% after 2000 cycles). The asymmetric two-electrode cell assembled from Co₃O₄@Ni-MOF/NF exhibits an energy density of 37.05 W h kg⁻¹ at a power density of 800 W kg⁻¹ with good long-term durability (75% capacitance retention after 10 000 cycles). Moreover, two charged cells can power a red light-emitting diode (LED) for up to 16 min, manifesting the great promise of Co₃O₄@Ni-MOF/NF for real energy storage devices.