Preparation Of Grapheme-carbon Nanotubes Supported Nanocatalysts And Their Performance In Methanol Electro-oxidation Reaction

Direct methanol fuel cell (DMFC) is an electrochemical device that can convert the chemical energy of a methanol fuel into electrical energy through chemical reactions on the interface of electrode and electrolyte with the advantages of high energy conversion efficiency?low-operation temperature and low emissions. However, the prohibitively high cost and insufficient durability of traditional platinum electrocatalysts have severely limited their widespread commercialization. So it is desirable to find new low-cost catalysts with high performance to replace or reduce the expensive and scarce Pt.Currently, one-dimensional (1D) CNTs and two-dimensional (2D) graphene sheets have received particular attention as superior supports, due to their unique structures and properties, for example:large specific surface area, excellent electrical conductivity, good electrochemical durability and mechanical stability. However, pristine CNTs are hydrophobic and surface-inert, and they generally need chemical oxidative modification and/or the use of polymeric surfactants to make them processable, moreover, graphene sheets tend to stack irreversibly, which greatly decreases the surface area and deteriorates electron transport. Based on the above questions and ideas, we design the work plan as follows:(1) A three-dimensional (3D) nitrogen-doped reduced graphene oxide (rGO)-carbon nanotubes (CNTs) architecture supporting ultrafine Pd nanoparticles is prepared and used as a highly efficient electrocatalyst. Graphene oxide (GO) is first used as a surfactant to disperse pristine CNTs for electrochemical preparation of 3D rGO@CNTs, and subsequently one-step electrodeposition of the stable colloidal GO-CNTs solution containing Na2PdCl4 affords rGO@CNTs-supported Pd nanoparticles. Further thermal treatment of the Pd/rGO@CNTs hybrid with ammonia achieves not only in situ nitrogen-doping of the rGO@CNTs support but also extraordinary size decrease of the Pd nanoparticles to below 2.0 nm. The resulting catalyst is characterized by scanning and transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. Cyclic voltammetry is used to evaluate the catalyst performance for the methanol oxidation reaction and the peak current density of Pd/NrGO@NCNTs was found to be 895.9 A g-1,which is almost 1.74 times and 7.47 times higher than those of Pd/rGO@CNTs (514.2 Ag-1) and commercial Pd/C (120.0 Ag-1) catalysts, respectively. Moreover, the Pd/NrGO@NCNTs catalystss show exceedingly high mass activity?superior durability and good anti-CO poisoning ability.(2) Three-dimensional reduced graphene oxide-carbon nanotubes supported copper nanosheets with platinum skim is prepared easily and used as a highly efficient electrocatalyst. Firstly, graphene oxide (GO) is used as a surfactant to well disperse pristine CNTs with a little CuSO4 for electrochemical preparation of 3D rGO@CNTs supporting Cu nanosheets, and then reacted with H2PtCl6 via a subsequent immerse reduction to realize the partial replacement of Cu with Pt to prepare the three-dimensional reduced graphene oxide-carbon nanotubes supported copper nanocubes with platinum skim electrocatalysts. The nanostructure and morphology of electrocatalysts are characterized by scanning electron microscope, transmission electron microscopy, X-ray diffraction, Raman spectrum, X-ray photoelectron spectroscopy. Cyclic voltammetry, chronoamperometry and CO stripping voltammograms were taken to evaluated the electrocatalytic performance. The results indicate that the Pt/Cu/rGO@CNTs not only equipped with outstanding electrocatalytic activity but also have a robust tolerance of catalyst poisoning.