Synthesis of Graphene/Metal Nanoparticle Composite via Quasi-Two-Step Reduction at Room Temperature for Electro-Oxidation of Ethanol inAlkaline Medium

Recently, renewable green energies such as fuel cells are increasingly considered due to depletion of fossil fuels and environmental pollution. Providing efficient and cost-effectivecatalysts is one of the most important programs in the development of fuel cells. One of the ways for improving the electrocatalytic activity of the fuel cell catalysts is to introduce a support material with an appropriate electrical conductivity and capability of dispersing and carrying thecatalyst particles effectively [1,2]. Among the various carbon materials for loading the catalyst nanoparticles, graphene, is one of the excellent candidate due to mechanical flexibility, chemicalstability, thermal conductivity, high surface area and its two-dimensional single or several atomiclayers [3]. In this work, we use a quasi-two-step reduction method at room temperature to produce a non noble effective metal nanoparticle-graphene composite for the electro oxidation of ethanol in order of application in direct alcohol fuel cells. Graphite oxide was synthesized from natural graphite powder using a modified Hummers’method. After the bath sonication (Struers Metason) and then centrifuging and removing unexfoliated materials, a suspension of graphene oxide (GO) was obtained. Nickel nanoparticles synthesized using a little amount of a diluted aqueous solution of NaBH4 as the reductant agent at room temperature. A suspension of GO (1 mg.ml-1) and an appropriate amount of polyvinylpyrrolidone wereprepared and followed by bath ultrasonication for 30 min. then GO colloidal dispersion added to the suspension of nickel nanoparticles and followed by stirring. A little amount of a dilutedaqueous solution of NaBH4 added to the suspension gradually. After completion the reaction, thehomogeneous suspension stirred for 12 h. All experimental steps were conducted at room temperature (25 °C). Finally, the black product was collected by centrifugation and then washed several times with ethanol and DI water. The resultant product was dried at 45 °C in air-oven andused for the following experiments. A catalyst ink of rGO/NiNP composite and FEP in IPA were prepared and dropped on the glassy carbon electrode at the loading of 0.034 mg.cm-2. The effect of temperature on the ethanol oxidation for rGO/NiNP composite catalyst wasinvestigated by performing voltammograms at scan rate of 100 mVs-1 at the temperatures of 25 and 60 ◦C (Fig. 1). Current density increased significantly with the higher temperature, i.e. peak current density was greater, indicating an increase in reaction kinetics

Keywords:

Quasi-Two-Step Reduction , Nickel Nanoparticles , Polyvinylpyrrolidone , Ethanol Oxidation