Preparation of Ni(OH)_2-graphene sheet-carbon nanotube composite as electrode material for supercapacitors

摘要

Ni(OH)_2-graphene sheet-carbon nanotube composite was prepared for supercapacitance materials through a simple two-step process involving solvothermal synthesis of graphene sheet-carbon nanotube composite in ethanol and chemical precipitation of Ni(OH)_2. According to N_2 adsorption/desorption analysis, the Brunauer-Emmett-Teller surface area of graphene sheet-carbon nanotube composite (109.07 m~2 g~(-1) was larger than that of pure graphene sheets (32.06 m~2 g~(-1)), indicating that the added carbon nanotubes (15 wt.%) could prevent graphene sheets from restacking in the solvothermal reaction. The results of field emission scanning electron microscopy and transmission electron microscopy showed that Ni(OH)_2 nanosheets were uniformly loaded into the three-dimensional interconnected network of graphene sheet-carbon nanotube composite. The microstructure enhanced the rate capability and utilization of Ni(OH)_2. The specific capacitance of Ni(OH)_2-graphene sheet-carbon nanotube composite was 1170.38 F g~(-1) at a current density of 0.2 A g~(-1) in the 6 mol L~(-1) KOH solution, higher than those provided by pure Ni(OH)_2 (953.67 Fg~(-1)) and graphene sheets (178.25 Fg~(-1)). After 20 cycles at each current density (0.2,0.4,0.6,0.8,1.0 and 1.2 A g~(-1)), the capacitance of Ni(OH)_2-graphene sheet-carbon nanotube composite decreased 26.96% of initial capacitance compared to 74.52% for pure Ni(OH)_2.