Properties of graphene/nano diamond composite electrode

Composite electrode of graphitized nano diamond (GND) and graphene was prepared to satisfy the requirements of super capacitor on higher energy density, higher power density and longer service life. GND was prepared by vacuum heat treating nano diamond (ND). Graphene/GND composite electrodes with different mass ratios were prepared by ultrasonic mixing method. The electrochemical performance of the electrodes was tested and their structures were analyzed. Resluts show that when the mass ratio is 4∶1, the prepared grahpene/GND composite electrode exhibited a good characteristic of double layer capacitor, whose voltammetric curve is almost rectangular and the shape remains nearly stable as scanning speed changes. When the scanning speed is 2 mV/s and the solution is 0.5 mol/L K₂SO₄, the electrode has a high specific capacitance of 103.3 F/g which decays no more than 0.95% after 1000 scanning cycles, showing excellent cycling stability. TEM result indicates that graphene layers are formed on the surface of nano diamonds after heat treatment and that the surface of graphene is restricted by the diamond structure. The graphene layer spacing gradually increases from the inside to the outside and improves the conductivity of the electrode. The SEM analysis concludes that GND is uniformly adhered to the surface of the graphene, forming blocks between graphene sheets and preventing messy graphene stack, which is good for the diffusion of electrolyte and increases the specific capacitance of composite material and its electrochemical performance.