Synthesis Of Graphene Support Pd Based Catalysts Composites And Their Electrocatalytic Properties For Formic Acid Oxidation

Direct formic acid fuel cell （DFAFC） have wide applications in low temperature fuel cell due to thelow-pollution, abundant sources, high energy efficiency, the easy storage andtransportation of the fuel. At the presence, we have found that the calalytic activity of Pd for formicacid oxidation is higher than that of other metals. Moreover, Pd is abundant on the earth. It is widelyemployed as an essential and effective catalyst in DFAFC systems. The corresponding electrocatalyticbehavior is closely related to the category and surface properties of the carbon supports. Furthermore,the dispersion, particle size and distribution of noble metal catalyst are also directly dependent uponthe structure and composition of carbon supports. The recent emergence of graphene nanosheets hasopened a new avenue for utilizing the new carbon material as a support due to their high specificsurface area, excellent electronic conductivity and high chemical stability. Recently, graphene hasreceived attention as the catalyst support for fuel cell applications. However, the superficial wettingability, surface area and electronic conductivity of graphene still remain to be great limitations insome aspects, therefore, hindering its further applications as a carbon support in DFAFC. To reducethe cost of fuel cell, the total amount of expensive noble metal catalysts has to be reduced, but theoverall performance of fuel cells have to remain unchanged or higher. In this dissertation, newstructure of classical catalysts and new catalyst supports of graphene with excellent wetting abilityand high conductivity in fuel cells have been developed and investigated. The micrographs, structureand properties of the catalysts applications have been investigated. The activity and stability ofinfluence has been evaluated the regularity of components and structure for formic acid oxidation.And discusses the connections between the graphene surfaces and metal nanoparticles, providetheoretical support for the DFAFC of application prospect. The main points in this dissertation aresummarized as follows:1. Comparison of catalytic performance on different carbon materials supported Pd catalysts forformic acid oxidation. The graphene nanosheets supporting Pd catalysts were prepared by a single-stepchemical reduction method.The electrocatalytic performance for formic acid oxidation of the preparedPd/graphene composite was studied as an electrode material in comparison with the compositecatalysts based on the other carbons （MWCNTs, SWCNTs, and Vulcan XC-72carbon black）. It wasfound that the Pd/graphene composites had better catalytic activity than the other catalysts towardformic acid oxidation. In order to enhance the wetting ability of graphene, the graphene with aminophenyl groups is successfully synthesized as catalyst-supports by a nucleophilic ring-openingreaction between graphene oxide （GO） and p-phenylenediamine （PPD）. The modified graphene sheetswere used as support materials for Pd NPs, and the assemblies’ electrochemical properties for formicacid oxidation were investigated. Palladium nanoparticles with a diameter of4.2nm were depositedon modified graphene. The electrochemical results showed Pd catalysts supported on modifiedgraphene for formic acid oxidation exhibite an especially high current density of112.36mA mg^-1, itwas1.6times higher than that of Pd on untreated graphene. Therefore, the stability of Pd catalystssupported on modified graphene was also significantly improved by introducing aminophenyl groupsgroups to graphene systems.2. The electrode material based on graphene nanosheets-MWCNTs （GNS-CNTs） composites wassynthesized by in situ reduction methods. Then, palladium nanoparticles （NPs） supported onGNS-CNTs by a microwave-assisted polyol process. The relationship between the different ratios ofGO to CNTs and the electrode activity was optimized. Compared to either Pd/Vulcan XC-72carbon,Pd/GNS, or Pd/CNTs catalysts, the Pd/GNS-CNTs catalysts exhibit excellent catalytic activity andstability for formic acid electro-oxidation when the weight feed ratio of GO to CNTs is5:1. Thesuperior performance of Pd/GNS-CNTs catalysts may arise from possess large surface areasutilization for NPs and the greatly increased electronic conductivity of the supports.3. The novel electrode material based on GO-polypyrrole （PPy） composites was synthesized by insitu chemical oxidation polymerization. Palladium nanoparticles （NPs） with a diameter of4.0nmwere loaded on the reduced graphene oxide （RGO）-PPy composites by a microwave-assisted polyolprocess. The activity and stability of influence has been evaluated the regularity of components forformic acid oxidation. Microstructure analysis showed that a layer of coated PPy film withmonodisperse Pd NPs is present on the RGO surface. The relationship between the different ratios ofGO to PPy and the electrode activity was optimized. The Pd/RGO-PPy catalysts exhibit excellentcatalytic activity and stability for formic acid electro-oxidation when the weight feed ratio of GO topyrrole monomer is2:1. The superior performance of Pd/RGO-PPy catalysts may arise fromutilization of heterogeneous nucleation sites for NPs and the greatly increased electronic conductivityof the supports.4. We have developed a solvothermal reduction method from an organic solution system inN-methyl-2-pyrrolidone （NMP） for the synthesis of the monodisperse palladium nanoparticlesdispersed on the reduced graphene oxide （RGO） sheets. While the detailed mechanism have discussed,the TOP、OAm and GO are recognized to be critical for attaining the monodisperse palladium NPs inthis organic solution system. This system was tested for potential use as an anode material through the electrooxidation of formic acid. The palladium nanoparticles with a diameter of3.8nm were loadedon RGO. The catalytic activity of Pd/RGO catalyst is1.4times higher than the Pd/Vulcan XC-72catalyst for the oxidation of formic acid. Moreover, both the stability of Pd/RGO catalysts and theability of CO tolerance were better than Pd/C catalysts.Using the same method, we prepared dendriticPd nanoparticles （DPNs） and small Pd nanoparticles （PNPs） supported on graphene with two degreesof reduction. In addition to being a commonplace substrate, GO plays a more important role relied onits surface groups, which serves as a shape-directing agent to direct the dendritic growth. In contrast,small Pd nanoparticles supported on RGO were formed. As a result, the catalytic activity ofDPNs/RGO catalyst is1.5times higher than the PNPs/RGO catalyst for the oxidation of formic acid.Moreover, both the stability of DPNs/RGO catalysts and the ability of CO tolerance were improved.5. We synthesized highly active Pd nanocube catalysts using graphene as supports via ahigh-pressure colloidal method by a novel two-step approach. The particle sizes of the catalysts arearound8nm with high dispersion. While the detailed mechanism have discussed, I-is recognized tobe critical for attaining the monodisperse Pd nanocube in this organic solution system. In contrast,small Pd sphere particles supported on RGO were formed by changing the etching agent. Theelectrochemical results indicated the catalytic activity of Pd nanocube/RGO catalyst is1.8timeshigher than the Pd sphere/RGO catalyst for the oxidation of formic acid.