NH4F assisted and morphology-controlled fabrication of ZnCo2O4 nanostructures on Ni-foam for enhanced energy storage devices

Abstract Four morphology-dependent ZnCo2O4 nanoarchitectures on Ni-foam with the aid of auxiliary reagent ammonium fluoride (NH4F) were facilely synthesized via a simple hydrothermal method and a consequent annealing process. With the gradual increase of NH4F, there was a morphological transformation from nanoflake, through nanowire@nanoflake and hetero-nanowire, to hierarchical leaf-like. The BET surface area and the specific capacitance at 1 A g−1 were both gradually improved, from 63.9 to 89.3 m2 g−1 and from 600 to 1700 F g−1, respectively, during the process of morphological change. The hierarchical leaf-like ZnCo2O4 had the lowest charge transfer resistance and the highest capacitive behavior, as well as considerable cycling performance (110% after 8000 cycles at 2 A g−1). A full button cell combining both anode material (AC) and cathode material (leaf-like ZnCo2O4) displayed satisfying energy density (63 Wh kg−1) and power density (795.5 W kg−1) as well as firm cycling performance (98% retention after 4000 cycles). The successful illumination of LEDs by the constructed full cell implied the promising practicability for future industrial green energy-storage devices usage of the ZnCo2O4 nanomaterials.