Preparation And Electrochemical Catalytic Properties Of Graphene Based Composite Materials

Direct alcohol fuel cells(DAFC) have been extensively investigated in the field of new energy sources as high efficiency and clean energy. The key to improve the efficiency and utilization of energy conversion is anode catalyst layer, and the most important research is catalyst materials. Since the advent of graphene materials, its application fields have been constantly expanded, especially it has been the first choice as catalyst support material in electrode for it has great specific surface area and excellent electrical conductivity. Pt and other precious metal materials are always used as catalyst for fuel cells with good catalytic effects while showing some problems. Therefore, this study focuses on finding a new economic nanoscale metal materials as catalysts and synthesizing graphene based metal composites with good performance and stability.The preparation methods of graphene/nickel-based composite materials were based on two conventional methods and a new method. As precursor material, the preparation of graphene oxide was firstly studied, and it was found that the higher quality film was obtained by the Hummers method without adding sodium nitrate. Then a chemical plating solution was made up, and nickel was plated on the surface of sulfonated-graphene by traditional chemical plating. The morphology of the obtained composite is regular and the uniform particle size of nano-nickel is well-distributed, while the process is complex; using a simple in situ reduction method to prepare the graphene nickel-based composite material, the key point lies in selection of reducing agent and dosage of surfactant. Study about the common reducing reagent of graphene oxide: hydrazine hydrate, sodium borohydride, hydrogen iodide reagent found that three different kinds of reducing agents have different reduction mechanisms to oxygen containing functional groups on the surface of graphene oxide, resulting in different final morphology and the most suitable reduction reagent is sodium borohydride. As usual surfactant agent, sodium dodecyl benzene sulfonate can help graphene surface be more hydrophilicity and wettability, which is contributed to the preparation of nickel composite materials, however, sodium dodecyl benzene sulfonate is oily, and adding the amount will make the sample morphology become worse. In alkaline conditions nickel ion would react with hydrazine hydrate to generate a complex material [Ni(N2H4)3]2+, the next step is to generate Ni. In the solution, the obtained graphene and nickel occurred meanwhile before compound, the preparation process and final sample morphology by this method is between two methods above. The method is simple and easy to repeat, and the morphology of the composite is good. The sample configurations of three methods are made to nano-catalyst coating materials, then tested for cyclic voltammetry and chronoamperometry in alkaline solution with alcohols to characterize catalytic oxidations of alcohols. As a result of special valence state and the structure change of nanometer nickel material, it is a good catalyst for catalytic oxidation of alcohols at room temperature. The results show that at room temperature the graphene/nickel nano-composites prepared by the last two methods can be the effective catalytic to catalyze oxidation of methanol and ethanol. In situ reduction method the methanol catalytic performance shows best when adding amount of nickel salt is 0.145 g, result shows that the starting voltage is 0.4 V, and peak current density value is 8.9 mA, maximum power is 6.23 mW, while catalytic ethanol catalytic oxidation effect is not obvious; in coordination compound method the catalytic performance shows best when the adding amount of nickel salt was 0.131 g, result shows that starting voltage is 0.326 V, peak current is 8.71 mA during the process to catalyst methanol, and the peak current is 2.273 mA, and power density value is 1.23 mW during the process to catalyst ethanol.