Preparation And Electrochemical Properties Of Graphene/Nickel Oxide Composites

With the continuous depletion of non-renewable resources such as oil and coal, and people pay more attention to the environmental protection. The world energy crisis and environmental problems has become the major issues in today, people have to looking for new energy to solve the two problems. The new energy is stored by the form of electrical energy, so it is the urgent need for a new green and efficient storage device. Supercapacitors as a new energy storage device, it has more than lithium batteries with high power density, and more than traditional capacitors with high cycle life and greater energy density. Supercapacitors has two kinds of energy storage mechanisms, one is the double layer capacitance mechanism, another is the pseudocapacitance mechanism. The carbon material which provide electric double-layer capacitance was composited with metal oxide which provide pseudocapacitance, and then the supercapacitor have better electrochemical performance due to it have electric double-layer capacitance and pseudocapacitance at the same time. In this paper, graphene/nickel oxide composites were synthesized by different alcohols, and study the electrochemical properties of this composites. The presence of alcohols is used as a substitute for highly toxic and highly irritating reducing agents to reduce graphite oxide to graphene. The main content in the following aspects:1. Graphite oxide (GO) as raw materials which prepared by the modified Hummers method, and then GO solution, Ni(NO3)2-6H2O solution and benzene alcohol (BnOH) was mixt according to a certain mixing ratio, after hydrothermal reaction and subsequent microwave heat treatment, we can get the graphene/nickel oxide composite (G/NiO). Selecting different hydrothermal temperature (100-250℃), in order to research the influence of hydrothermal temperature on the material. XRD was confirmed that the prepared material was graphene/nickel oxide composite. TGA and XPS test found that the G/NiO-200 (hydrothermal temperature is 200 ℃) is a kind of structural stability, the reduction degree is better, and the content of NiO is the highest. SEM and TEM test results show that the resulting graphene/nickel oxide composite is a kind of globule-sheet structure, NiO nano-particles evenly dispersed on the graphene nano-film. By the electrochemical performance test, it was found that the G/NiO-200 composite based supercapacitor which under the current density of 1 A g-1, the specific capacitance can be reached 530 F g-1. This capacitance is much higher than that of pure graphene based super capacitor, and also higher than G/NiO composite based supercapacitor in other hydrothermal temperature. After 5000 cycles, the supercapacitor still remains a specific capacitance of 490 F g-1 (92% retention of the initial capacity), exhibiting excellent cycling stability.2. Using the modified Hummers method to prepared Graphite oxide (GO), and then GO solution, Ni(NO3)2·6H2O solution and propylene glycol was mixt according to a certain mixing ratio, after hydrothermal reaction and subsequent microwave heat treatment, we can get the graphene/nickel oxide composite (G/NiO). In order to study the effect of reducing agent content on the material, the amount of propylene glycol was (0%,1%,5% and 10%) respectively. The results of XRD confirm that the prepared material is graphene/nickel oxide composite. And the results of TGA and XPS showed that when the amount of propylene glycol is 1%, the reduction effect of G/NiO-2 composites is good, and the content of NiO is the highest. SEM and TEM tests found that the prepared G/NiO composite is a globule-sheet structure, and the NiO nanoparticles were uniformly fixed on the graphene sheet. The results of electrochemical performance test show that G/NiO-2 composite based supercapacitor which under the current density of 1 A g-1, the specific capacitance can be reached 357 F g-1. This capacitance is higher that G/NiO composite based supercapacitor in other content of propylene glycol. After 10000 cycles, this supercapacitor still have a specific capacitance of 336 F g-1 (94% retention of the initial capacity), exhibiting excellent cycling stability.3. Graphite oxide (GO) was prepared by the modified Hummers method, and then GO solution, Ni(NO3)2- 6H2O solution and glycerol was mixt according to a certain mixing ratio, after hydrothermal reaction and subsequent microwave heat treatment, we can get the graphene/nickel oxide composite (G/N). In order to study the effect of reducing agent content on the materials, different glycerol content (0%,1%,5% and 10%) added respectively. XRD has proved that the prepared material is graphene/nickel oxide composite (G/N). TGA and XPS results showed that when glycerol amount is 10%, the prepared G/N-4 composite is a stable structure, reducing effect is good and NiO content is highest. After electrochemical performance test show that G/N-4 composite based supercapacitor which under the current density of 1 A g-1, the specific capacitance can be reached 322 F g-1. This capacitance is higher that G/N composite based supercapacitor in other amount of glycerol. After 10000 cycles, this supercapacitor maintain a specific capacitance of 317 F g-1 (98% retention of the initial capacity), exhibiting excellent cycling stability.