Fabrication of Ni₃S₂@polypyrrole core-shell nanorod arrays on nickel foam as supercapacitor device

A free-standing Ni₃S₂@polypyrrole core-shell nanorod arrays have been successfully prepared and been directly used as supercapacitor. First, needle-like Ni₃S₂ nanorods array was grown on Ni foam through a hydrothermal process, and was then electrochemically deposited with polypyrrole (PPy) layer. The composition, microstructure, and morphology of the obtained composite material have been studied by attenuated total reflection Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscope. Our results indicate that the needle-like Ni₃S₂ nanorods with diameter about 200 nm and 3 μm in length have grown evenly on Ni foam, and the thickness of the coated PPy layer can be tuned by the electrodeposition time. The electrochemical properties of the obtained free-standing Ni₃S₂/Ni@PPy composite foam have been evaluated by a three-electrode system. Our results reveal that the composite foam with the PPy shell layer about 300 nm in thickness displays the best performance, and the area specific capacitance was measured to be over 5 times that of the Ni₃S₂/Ni foam to reach 55.4 mF/cm². The improvement has been attributed to the unique hierarchical core-shell microstructure and to the proper amount of PPy deposition. Moreover, the electrochemical stability of the material has been checked to indicate its potential as high-performance supercapacitors.