Construction And ORR Performance Of Carbon-supported Platinum-based Binary Alloy Catalyst

Proton exchange membrane fuel cells（PEMFCs）are devices that can directly convert chemical energy into electrical energy.They have some advantages of low operating temperature,fast start-up speed,clean and efficient,which are of great development and utilization value.In PEMFCs,the cathodic oxygen reduction reaction（ORR）kinetics is slow,so a large amount of catalyst is needed to increase the reaction rate.So far,the most commonly used catalyst is still platinum-carbon（Pt/C）catalysts in PEMFCs.But due to the low utilization of Pt and poor durability,the large-scale application of PEMFCs has been greatly restricted.Therefore,enhancing the ORR activity of Pt-based materials and improving the utilization and durability of Pt atoms can effectively promote the commercialization of PEMFCs.Alloying Pt with other metals is a common strategy that takes into account activity,utilization and durability.However,the synthesis of Pt-based alloys often requires high-temperature sintering,which is likely to cause serious agglomeration,and greatly reduces the activity and durability of the Pt-based catalyst.Pt atom utilization.Based on this,this paper has carried out the following two aspects of work:（1）To solve the problem of low utilization rate of Pt atom,a kind of high performance and high dispersion Pt Co/C binary alloy catalyst was prepared by the method of freeze drying and high temperature reduction.In this paper,the reduction temperature and Pt/Co theoretical mole ratio during the preparation process were explored.Meanwhile,characterization and performance analysis were carried out.The morphology characterization of Pt Co/C binary alloy showed that the Pt Co binary alloy prepared by the freeze-drying procedure dispersed uniformly on the support and had no obvious agglomeration phenomenon.Electrochemical performance tests showed the ORR half-wave potential of Pt Co/C-400-3 catalyst was up to 0.945 V in acidic medium,and the positive shift of 31 m V compared with commercial Pt/C catalyst.And it showed high mass activity(0.37 A/mg _Pt)and specific surface activity（1.13 m A/cm²）.The score was2.03 and 4.45 times higher than that of commercial Pt/C.After 20,000 electrochemical cycles,Pt Co/C showed higher stability than commercial Pt/C catalysts.（2）Aiming at the problem of poor durability of Pt-based catalysts,a Pt Ni/Fe NC binary alloy supported on a three-dimensional porous Fe and N co-doped carbon support material was prepared.Through the characterization of the support material,it is found that Fe NC material has a high degree of graphitization,high specific surface area and porous structure,which can improve the conductivity and mass transfer of the catalyst,and its surface Fe and N atoms can effectively anchor Pt and Ni particles,which can enhance the stability of the catalyst.The morphology characterization of the Pt Ni/Fe NC alloy catalyst shows that its dispersion is uniform,and the average particle size is about2.89 nm.The electrochemical performance test shows that the ORR half-wave potential of the Pt Ni/Fe NC binary alloy catalyst in acidic medium reaches 0.915 V,which is 28 m V higher than commercial Pt/C（0.886 V）.And the area specific activity（0.861 m A/cm²）and quality activity(0.518 A/mg _Pt)are 3.6 times and 3.34 times that of commercial Pt/C,respectively.Through the durability test of 10,000 cycles,the attenuation degree of the Pt Ni/Fe NC alloy is less than that of the commercial Pt/C,indicating that the stability of the Pt Ni/Fe NC alloy has been improved to a certain extent.