Construction And Control Of Transition Metal Phosphide Modified Multi-walled Carbon Nanotube Pt-based Composite Catalyst

In recent years,the lack of energy and environmental pollution are more and more important issues for the sustainable development of human society,and the development of green,efficient,and environmentally friendly new energy sources has become a hot issue in scientific research.Direct methanol fuel cells（DMFCs）are ideal power sources due to their advantages of abundant fuel sources,high theoretical energy ratio,clean environment,and small size.Nowadays,precious metal Pt is still the preferred catalytic material for DMFCs,however some problems including the scarce resources,high cost,weak resistance towards CO poisoning,poor stability and so on hinder the large-scale commercialization of DMFCs.Therefore,improving the support material properties and reducing the amount of precious metals are the main research directions of anode catalysts.Based on the above objectives,we mainly carried out the following basic research work on the basis of the current development status of anode catalysts:Firstly,Pt-MoP/MWCNTs catalysts with small particle size MoP modified Multi-walled Carbon Nanotube Pt-based catalyst were successfully prepared by one-step hydrothermal,phosphating and Na BH4 reduction method.The effects of hydrothermal time,relative content of metal precursor and multiwalled carbon nanotubes on the performance of the catalyst were investigated.TEM indicates that the diameter of the MoP is about 4 nm.And the electrochemical measurements showed that the hydrothermal time is 24 h,and the mass ratio of metal precursor to multiwalled carbon nanotube is 2.5:1.Simultaneously the obtained Pt-MoP/MWCNTs-3 exhibited excellent methanol electrooxidation activity and stability,its mass specific activity was up to 1063 m A mg_Pt^-1,which is 2.7-and 3.8-fold higher than that of commercial Pt/C(393 m A mg_Pt^-1)and homemade Pt-MWCNTs(278 m A mg_Pt^-1)catalysts,respectively.Moreover,the CO-stripping experiments also showed that Pt-MoP/MWCNTs-3 exhibits the lowest onset potential for CO oxidation,with a negative shift of about 0.11 V contrasting with the Pt-MWCNTs catalyst,indicating the composite catalyst has a superior CO tolerance.Secondly,it’s clearly found that MoP could significantly promote the catalytic activity and stability of catalysts in acidic media according to the research in chapter 3,therefore the second metal Ni was introduced into MoP based on the aboved study.Similarly,the hydrothermal time and the mass ratio of（NH₄）₆Mo₇O₂₄·4H₂O and Ni（NO₃）₂·6H₂O were optimized to construct the support material.The electrochemical measurements presented that the molar ratio of Ni salt and Mo salt was 1:1,and the Pt-NiMoP/MWCNTs catalyst prepared under the condition of 180℃hydrothermal reaction for 24 h shows excellent methanol oxidation performance.