Preparation Of Tungsten Carbide Loaded On Carbon Composite And Its Electrocatalystic Performance For Methanol Oxidation

In recent years,tungsten carbide is the promising material to take place of noble metal used in Direct Methanol Fuel Cells(DMFCs)has a wide range of application and development.In this subject,for the ethanol as the dispersing agent,the composite material WC/C by the method "solution grafting-synchronous reduction and carbonization",the mesoporous molecular sieves SBA-15 mixed with tungsten and ordered mesoporous carbon(OMC)as the template and support.The surface topography,phase structure and chemical composition of WC/C is studied by transmission electron microscopy(TEM),X-ray diffraction(XRD),low-temperature N2 adsorption desorption measurement(BET).At the same time,the catalytic properties of methanol electro-oxidation reaction are measured by cyclic voltammetry and in situ FTIR technique.Through the study,the amorphous carbon/tungsten carbide composite material was synthesized using tetraethyl orthosilicate(TEOS)as silica precursor,tungstic acid prepared by tungsten powder and hydrogen peroxide,and EO20PO70EO20(P123)as structure-directing reagent.After temperature-programmed carburization(TPC),the structure of material has been characterized using XRD,BET and TEM.The results show that tungsten carbide exists as a single WC' phase under the 900 ?TPC,some WC inside the framework of SBA-15 and others in aggregate outside the channel surface.The deposit carbons,which are coated WC parcitle surface when preparing WC phase,covered the electro-catalytic active sites so that the catalytic methanol oxidation propriety of WC electrodes was difficult to reach their theoretical value.For the CMK-3 as the template,the composite material WC/OMC,the study found that the best reaction conditions is 50%tungsten thermally reduced in the 900 ? for 3h under the H2/Ar.In this method,OMC acted both as the support and the carbon sources and deposit carbon which covers the active sites can be effectively avoided.Electro-catalytic properties of methanol oxidation on the OMC/WCs electrode have been investigated using cyclic voltammetry and in situ FTIR technique,to study the process of methanol electrocatalystic oxidation on the surface of WC particle.The results showed that there was only one characteristic methanol oxidation peak on about 0.73V during the whole potential scan on the OMC/WCs electrode surface,and an improved CO tolerance of the WC surface.It proved that tungsten carbide had good electro-catalytic property close to that of the Pt-based materials for methanol oxidation and provided a new idea for developing electrode materials in the future.Meanwhile,it also studied that the molecular sieve adsorped Pt4+ ion material(Pt4+-NH2-MCM-41)exhibited catalytic activity in the methanol electro-oxidation.The characterization carried out by X-ray photoelectron spectroscopy,X-ray diffraction,and N2 adsorption desorption measurement pointed out that Pt was adsorbed on the NH2-MCM-41 surface as the oxidation state(Pt4+)and the surface area of Pt4+-NH2-MCM-41 was up to 564 m2/g.It made the dosage of Pt4+ in the composite materials to the minimum.Transmission electron microscopy and elemental mapping indicated a homogeneous distribution of Pt4+ through-out all surface of the mesoporous materials.The results showed that it is first proved that platinum ions had good electro-catalytic property for methanol oxidation and the Pt4+-NH2-MCM-41 electrode exhibited catalytic activity in the methanol electro-oxidation with the apparent activation energy being 49.29 kJ/mol,and the control step of methanol electro-oxidation was the mass transfer process.