Ni Foam-Ni₃ S₂ @Ni(OH)₂ -Graphene Sandwich Structure Electrode Materials: Facile Synthesis and High Supercapacitor...

A novel Ni foam-Ni₃ S₂ @Ni(OH)₂ -graphene sandwich-structured electrode (NF-NN-G) with high areal mass loading (8.33 mg cm^-2 ) has been developed by sulfidation and hydrolysis reactions. The conductivity of Ni₃ S₂ and Ni(OH)₂ were both improved. The upper layer of Ni(OH)₂ , covered with a thin graphene film, is formed in situ from the surface of the lower layer of Ni₃ S₂ , whereas the Ni₃ S₂ grown on Ni foam substrate mainly acts as a rough support bridging the Ni(OH)₂ and Ni foam. The graphene stabilized the Ni(OH)₂ and the electrochemical properties were effectively enhanced. The as-synthesized NF-NN-G-5mg electrode shows a high specific capacitance (2258 F g^-1 at 1 A g^-1 or 18.81 F cm^-2 at 8.33 mA cm^-2 ) and an outstanding rate property (1010 F g^-1 at 20 Ag^-1 or 8.413 F cm^-2 at 166.6 mA cm^-2 ). This result is around double the capacitance achieved in previous research on Ni₃ S₂ @Ni(OH)₂ /3DGN composites (3DGN=three-dimensional graphene network). In addition, the as-fabricated NF-NN-G-5mg composite electrode has an excellent cycle life with no capacitance loss after 3000 cycles, indicating a potential application as an efficient electrode.