Preparation Of Heteroatom-doped Carbon Black-supported Pt Catalyst And Study Of Its Oxygen Reduction Performanc

Due to the increasing energy demand and worsening environmental problems,proton exchange membrane fuel cells（PEMFCs）have attracted wide attention for their advantages of low operating temperature,high specific power,environmental protection and high efficiency.The oxygen reduction reaction（ORR）at its cathode needs electrocatalyst to accelerate the reaction speed because of its slow kinetics.At present,the commercial cathode catalyst of PEMFCs is usually the precious metal platinum（Pt）based catalyst.However,due to the problems of high price,high dosage and poor stability of Pt based catalyst,further optimization is needed.In recent years,researchers have developed heteroatom doping strategies,which successfully doped other heteroatoms into the catalyst system,using the interaction between heteroatoms and Pt to further improve the catalytic activity and stability of the catalyst.In this paper,carbon black-supported Pt catalysts doped with heteroatoms（N,P,S）have been synthesized by a very simple one-pot pyrolysis method.The structure of the catalyst was tested by transmission electron microscopy（TEM）,X-ray diffraction（XRD）and Raman spectroscopy,and the electrocatalytic activity of the catalyst was characterized by cyclic voltammetry（CV）and linear scanning（LSV）.The effect of heteroatomic doping on the catalytic performance of the catalyst was studied.The main research results are as follows:（1）Using melamine（N source）,ammonium dihydrogen phosphate（P source）and thiourea（S source）as dopants and acetoacetone platinum（Pt（acac）₂）as Pt source,the single heteroatom doped carbon black supported Pt catalyst was prepared by high temperature pyrolytic reduction method.The effects of pyrolysis temperature,Pt loading capacity and heteroatom doping amount on the activity and stability of catalysts were investigated.It was found that the catalytic activity of Pt/BP-N₂₅₀-900-20%at 900℃was the best when the ratio of N doped precursor to carbon black was 5:1 and the theoretical Pt loading was 20 wt.%.In addition,the performance of P-doped and S-doped catalysts is poor.TEM data showed that the particle size distribution of the N heteroatom doped catalyst was different,and there were large particles with a particle size of about20nm,and the average particle size was about 3.34nm.N heteroatoms mainly form pyridine nitrogen and graphite nitrogen,and the interaction between them and Pt can promote the catalytic activity of Pt.The catalyst showed excellent ORR catalytic activity under acidic conditions.Its initial potential E_o was 0.931V and half wave potential E_1/2was 0.803V.The catalytic activity was better than that of commercial Pt/C catalyst,but its stability was not good.（2）Carbon black-supported Pt catalysts doped with diheteroatoms（N S、N P、S P）were prepared by pyrolytic reduction method.It is found that the N and S co-doped carbon black-supported Pt catalyst(Pt/BP-N₂₅₀S₂₅₀-900-30%)has the best catalytic performance among the three systems.N,P co-doped and S,P co-doped carbon black-supported Pt catalysts have poor performance.The distribution of metal particles in the catalyst is relatively uniform,the average particle size is about 3.26 nm,and has a large specific surface area and small mesoporous pores,which can further increase the proportion of pyridine nitrogen and graphite nitrogen.At the same time,the doping of S element has an obvious effect on the stability of catalyst.The catalyst showed excellent ORR catalytic activity under acidic conditions,with initial potential E_o of 0.962 V,half-wave potential E_1/2 of 0.821 V,and attenuation of only 40 m V after 5000 CV cycles,both of which were better than commercial Pt/C catalysts.In this paper,a very simple high-temperature pyrolytic reduction method was used to study the effects of single and double heteroatom doping of carbon black support on the composition of Pt-based catalysts and the size of Pt particles,and to explore the effects of different heteroatom types on the performance of catalysts.The process path is simple,effective and easy to scale up,which provides a new idea for the large-scale preparation of fuel cell catalyst.