Purposely synthesis of hierarchical CuS nanoflowers composed of ultrathin nanoflakes with exposed (0 0 1) facets using a solvent-template ionic liquid and their application in supercapacitors

Two hierarchical CuS nanostructures assembled by nanoflakes with exposed (0 0 1) facets are purposely synthesized using ionic liquid 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) as solvent-template. [Bmim]Cl can act as efficient template for the formation of flake-like building blocks by adsorbing on the (0 0 1) facet of CuS. More importantly, the viscosity of [Bmim]Cl can be altered by changing the temperature; thereby, the self-assemble process of the building blocks can be controlled and accordingly the shapes of the products are “tailored”. The structural properties of the as-formed compact CuS nanoflowers (C-CuS) and loose CuS nanoflowers (L-CuS) are tested by XRD, SEM, TEM, HRTEM, and XPS, and the growth mechanisms are discussed in depth. When used as the electrode materials for supercapacitors, C-CuS exhibit higher specific capacitance and better rate capability than L-CuS. The improved capacitive performance of C-CuS may be due to the structural synergistic effect of ultrathin building units and dense hierarchical nanostructure.