Structure And Performance Of Platinum-metal Nitride Catalysts Supported On Carbon Nanotubes For Oxygen Reduction Reaction

The efficiency of fuel cell is mainly determined by the catalyst on the electrode.At present,the commercial Pt/C catalyst has the disadvantage that the combination of the carbon support and the metal active component platinum is not strong.In the long run of the fuel cell,carbon black is easily corroded,resulting in the aggregation or falling off of the Pt catalyst,which leads to the decline of the service life of the catalyst.Therefore,it is necessary to develop new catalysts with high activity,high stability and corrosion resistance and study their catalytic mechanism.In view of the disadvantages of high cost and poor stability of the current fuel cell cathode catalyst,this paper focuses on the research of platinum based catalysts from three aspects: synthesis method,promoter addition and support selection,and discusses the relationship between catalyst composition and catalyst performance.The specific contents are as follows:1.In this paper,CoCl₂·6H₂O,TiCl₄ as raw materials,CNT as the support,the CNT loaded multi component metal oxide precursors were prepared by the sol-gel method,and the catalyst for the preparation of Co-Ti-N/CNT was successfully prepared by high temperature reduction in NH3 atmosphere.The study shows that a series of Co-Ti-N/CNT catalysts with different cobalt and titanium ratio and carbon nanotube support were prepared by sol-gel method and ammonia reduction sucessfully.The active component is Co-N of cobalt metal nitride,at the same time,the reaction also produces nitrogen compounds of titanium,which is supported on carbon nanotubes as a co-catalysts.In the reaction process,carbon nanotubes can combine with nitrogen to form C-N structure.The oxygen reduction peak potential of theseries of catalysts is about 0.4 V?vs.RHE?,and the onset potential is about 0.7 V?vs.RHE?.Among Co-Ti-N/CNT catalysts,the activity of n Co: n Ti=1:10 sample changed little before and after acid treatment,and the onset potential of oxygen reduction was maintained at about 0.73 V,and the catalyst activity was better than other Co-Ti-N/CNT catalysts.The process of oxygen reduction catalyzed by Co-Ti-N/CNT catalyst is mainly controlled by two electron reaction paths.2.The Pt-Co supported on Ti N-CNT catalyst Pt-Co/Ti N-CNT prepared by NaBH₄ reduction method has good oxygen reduction activity.From the SEM diagram we can see that the catalyst surface was uniform.XRD showed that platinum and cobalt are in alloy form loading on Ti N-CNT.According to the onset potential of catalyst,the activity size can be ordered as: Pt1Co3/Ti N-CNT>Pt3Co1/Ti N-CNT>Pt/Ti N-CNT>Pt1Co1/Ti N-CNT.The oxygen reduction reaction of the series of catalysts is mainly a four electron reaction process.Compared with 40 wt% commercial Pt/C,the catalyst prepared has a relatively high activity while using a smaller amount of Pt.3.H₂ PtCl₆·6H₂O,CoCl₂·6H₂O,TiCl₄ and CNT were used as raw materials,citric acid were added as complexing agents and undering heat treatment in ammonia atmosphere.This method was first applied to the preparation of Pt-Co/Ti N-CNT catalysts.The SEM and TEM spectra showed us that there are homogeneous particles on the surface of CNT in Pt-Co N/Ti N-CNT samples.Combined with XRD,TEM and XPS analysis,the uniform micro particles are nanoparticles of Pt,Co N and Ti N.The oxygen reduction onset potential of the Pt0.3Co N/Ti N-CNT catalyst is 0.812 V?vs.RHE?,and the one of 40 wt% commercial Pt/C is0.789 V,while the Pt loading in Pt0.3Co N/Ti N-CNT is only 22.5 wt%.Through the K-L curve,the electron transfer number of each sample is calculated.The number of electron transfer of the catalyst in Pt-Co N/Ti N-CNT is close to four.The oxygen reduction reaction on the surface of the catalyst is a four electron reaction path,and the oxygen is directly reduced to H₂ O.The results of Tafel curve analysis show that the tafel curve slope of Pt-Co N/Ti N-CNT catalysts are close to theoretical value-60 m V·dec-1in low current density region.At the same time,the stability test of acid and methanol shows that the methanol resistance of Pt0.3Co N-Ti N-CNT and Pt0.5Co N-Ti N-CNT samples are superior to commercial Pt/C,and the promoter Co N and Ti N have an important role in improving the tolerance of methanol.