Morphology control and capacitive performance of Co₃O₄ nanostructures synthesized by NH₄F-assisted hydrothermal on Ni foam

Co3O4 is considered as an excellent capacitive materials for advanced supercapacitors. In this work, three different morphologies of Co3O4 nanostructures, nanowires, nanosheets, both nanowires and nanosheets structure were prepared by the hydrothermal reaction and subsequent heat treatment. The morphological evolutions of different intermediates at different reaction stages were examined and we proposed the mechanism of NH4F regulating the morphology. It was found that NH4F possibly controls the species and morphology of intermediates by adjusting the pH of the hydrothermal system. Finally, the Co3O4 with mixed structure exhibits a specific capacitance of 1005.4 F g(-1) at 2 A g(-1), and its capacitance retention can maintain to be 99.5% even after 4000 cycles. The excellent electrochemical performance is mainly attributed to the nanostructure composed of both hexagonal nanosheets and needle-like nanowires. We believe this work provides insights for Co3O4 electrode with multi-morphological nanostructures used for the development of advanced supercapacitors.