Pt-based Catalysts With Hollow Structure As Highly Active Electrocatalysts For Oxygen Reduction Reaction

Proton exchange membrane fuel cells（PEMFCs）are renewable energy devices for automobiles and portable electronic devices,with low operation temperature,high energy conversion efficiency and low pollution emission.At the same time,as the growing demand for renewable energy,fuel cell technology as a substitute to burn energy are of great importance in resolving the present energy crisis.To date,great efforts have focused on reducing the cost,volume,and weight of fuel cells at a rapid pace.One of the key approaches is to develop new techniques for making extremely active and stable cathode catalysts for PEMFCs.The advent of nanoscience and nanotechnology provides new opportunities in the improvement of the activity and durability of electrocatalysts for the oxygen reduction reaction（ORR）.Pt-based nanocatalysts are irreplaceable for proton exchange membrane fuel cells（PEMFCs）for its excellent performance,while the low reserves and high cost of Pt severely impede their commercialization.Tremendous efforts have been devoted to reduce the amounts of precious metals and improve their electrocatalytic performance at the same time.By rationally tuning their size,shape,composition and architecture,noble metal nanocrystals have been developed,as well as highly active ORR nanoelectrocatalysts.The main research contents of this paper are as follows:We synthesized Co nanowires with diameter of about 40 nanometers by modified solvothermal method.Hollow PtCo nanotubes on carbon catalysts were prepared in which chloroplatinic acid was served as displacer and suitable acid as etching agent.The effects of preparation conditions on the structure and electrocatalytic performance of the catalysts were investigated.The results showed that H-PtCo NTs/C catalyst prepared under the conditions of80 min replacement time,4 h etching time,600?L hydrochloric acid and 30℃temperature had good ORR activity.The ORR test and evaluation of the synthesized H-PtCo NTs/C and commercial Pt/C electrocatalyst were carried out.The mass activity and surface activity of the as-synthesized H-PtCo NTs/C electrocatalyst are 0.592 A mg_pt^-1 and 3.900 m A cm^-2,respectively,which are 4.05 times and 16.67 times higher than those of commercial Pt/C.H-PtCo NTs had a high mass activity retention rate after 40 k potential cycles,which is close to80%.Therefore,H-PtCo NTs catalysts with high oxygen reduction activity and stability were prepared in this chapter.We synthesized the sacrificial templates of Co nanostrings with a diameter of about 350nm were prepared by simple ethylene glycol reduction method.Based on the above sacrificial template method,we prepared a series of H-PtCo SSs catalysts under different experimental conditions.The results showed that H-PtCo SSs/C catalyst prepared under the conditions of 80min replacement time,2 h etching time,600?L hydrochloric acid and 30℃temperature had good ORR activity.The ORR test and evaluation of the synthesized H-PtCo SSs/C and commercial Pt/C electrocatalyst were carried out.The mass activity and surface activity of the as-synthesized H-PtCo SSs/C electrocatalyst are 0.431 A mg_pt^-1 and 2.834 m A cm^-2,respectively,which are 2.95 times and 12.11 times higher than those of commercial Pt/C.H-PtCo NTs had a high mass activity retention rate after 40 k potential cycles,which was 82.8%.Therefore,H-PtCo SSs catalysts with high oxygen reduction activity and stability were prepared in this chapter.Both the slightly large size and one-dimensional structure of hollow Pt-Co material prepared in this chapter,can increase the binding force between the Pt atoms and the carbon support,and avoid the agglomeration of Pt particles,so the stability is further improved.To some extent,the hollow structure can improve the utilization rate of platinum and the activities of oxygen reduction reaction.