Preparation And Electrochemical Properties Of Pt/WC/MWCNTs Nanocomposite Catalysts

Direct methanol fuel cell（DMFC）is a new energy conversion device that directly converts chemical energy into electrical energy by using liquid or gaseous methanol as fuel.It is considered to be ideal power sources for portable electronic devices and automobiles because of its high energy densities,affluent fuel sources,environmentally friendly and easy operation.Presently,Platinum（Pt）is still the most commonly used catalyst for both anode and cathode in DMFC.Pt resources are limited and expensive,and the coverage of platinum surface active sites leads to the reduction of catalytic efficiency,which greatly limits the commercial development and application of DMFC.The arrangement of atoms on the main crystal surface of Transition metal carbides（TMCs）is similar to that of Pt.This kind of surface electronic structure makes part of TMCs display a Pt-like catalytic behavior,so there’s a lot of attention in the field of fuel cell catalyst supports.The traditional method of synthesizing Pt/TMCs can not make sufficient contact between Pt and TMCs,which leads to catalytic activity of TMCs,no evident synergistic catalytic effect and low activity of the catalyst.In view of the above problems,Pt/WC/MWCNTs nanocomposite catalyst was prepared by using a controllable synthesis process as a DMFC catalyst in this paper.The main research contents can be summarized as follows:（1）The Pt/（WC）_x/MWCNTs nanocomposite catalysts with different mass fractions of tungsten carbide（WC）were prepared by"one-step"in situ reduction.Their structure,morphologies and composition were characterized by X-ray diffraction（XRD）,transmission electron microscopy（TEM）,Scanning Electron Microscopy（SEM）and Raman measurements.The results show that CO adsorbed on Pt surface is easier to be removed when Pt atoms and WC molecules are in full contact.The more active sites of Pt and WC are exposed,the higher the catalytic activity.When the mass fraction of WC is 15%,the surface particle size of Pt/（WC）₁₅/MWCNTs is the smallest and uniform,the particle sizes are about 4.62 nm.The electrochemical performance test results show that Pt/（WC）₁₅/MWCNTs exhibit excellent electrocatalytic performance and stability for methanol and ethanol electrooxidation compared with commercial catalyst Pt/C（ETEK）and other prepared catalysts.（2）The same molar ratio of Pt/WC/MWCNTs and Pt/WMoC/MWCNTs nanocomposite catalysts were prepared by"one-step"in situ reduction.Their structure and morphologies were characterized by XRD,TEM and SEM measurements.The results show that the grain size can be refined by adding the doping element Mo.The surface particles of Pt/WMoC/MWCNTs are small and uniform,with the average particle sizes are about 7.41 nm,while the average particle sizes of Pt/WC/MWCNTs are about 16.51 nm.Grain size refinement helps to increase catalytic active area,thus improving the catalytic activity in electrochemical reactions.The electrochemical performance test results show that the electrochemically active aurface area of Pt/WMoC/MWCNTs is 2.4 and 3.1 times higher than that of ETEK and Pt/WC/MWCNTs,respectively.Meanwhile,Pt/WMoC/MWCNTs demonstrates excellent stability and high resistance to CO poisoning for methanol and ethanol electrooxidation.