Hollow NiS@CoS with core-satellite nanostructure derived from metal-organic framework (MOF)-on-MOF hybrids as an electrode material for supercapacitors.

Metal-organic frameworks (MOFs) have found wide applications in the field of supercapacitors due to their highly controllable porous structure, big specific surface area, and abundant chemical functional groups. MOF-on-MOF hybrids not only enhance the composition of MOFs (such as ligands and/or metal centers) but also provide greater structural diversity. By utilizing MOFs as precursors for preparing sulfides, the unique characteristics and inherent structure of MOFs are preserved but their conductivity and capacitance are enhanced. This study successfully synthesized hollow-structured NiS@CoS derived from an Ni-MOF@ZIF-67 hybrid structure, where the Ni-MOF serves as the core and ZIF-67 as the satellite. The NiS@CoS electrode demonstrated a specific capacity as high as 747.3 C g at 1 A g, and it could still maintain 77% of its initial capacity at 10 A g. Furthermore, the assembled NiS@CoS//AC hybrid supercapacitor (HSC) device achieved a maximum energy density of 30.8 W h kg when the power density was 750 W kg. The device exhibited remarkable cycling durability, retaining 85.4% of its initial capacitance after 5000 cycles. Therefore, the derived functional materials based on MOF-on-MOF provide a more scalable and promising approach for the preparation of efficient electrode materials.