The Research On Oxygen Reduction Reaction Performance Of M-N-C Catalysts Based On Porphyrin Framework

The growing energy and environmental concerns drive us to develop environmentally friendly and sustainable energy conversion and storage technologies.To date,clean energy devices（e.g.,fuel cells and metal-air batteries）have been rapidly developed,but their efficiency and commercial application are limited by the slow cathodic oxygen reduction reaction（ORR）.Pt-based catalysts have been widely used as efficient catalysts to promote ORR kinetics,but the large-scale application in fuel cells are limited by their high cost,scarce resource and poor stability.Therefore,it is particularly important to develop cheap and abundant non-noble metal-based catalysts.It is found that transition metal and nitrogen co-doped carbon-based catalysts（M-N-C）are very promising ORR catalysts.They show comparable ORR activity to noble metal catalysts,and they also have good stability and good methanol tolerance.Although great progress have been achieved for the development of M-N-C catalysts,the process of preparing M-N-C catalysts at high temperature is complicated and tedious,and the energy consumption is high.Based on this,we prepare a series of metal porphyrin framework based M-N-C catalysts by using a simple one-pot method.Finally,M-N-C catalysts with high ORR performance were obtained.（1）Preparation of M-N-C catalysts based on metalloporphyrin framework.In this section,four types of metal porphyrin-based M-N-C catalysts were successfully synthesized by one-pot reaction of 2,2’-bithiophene-5,5’-dicarbaldehyde,pyrrole and transition metal ions（Co,Mn,Zn,Ni）acetate.The structure characterization and ORR performance of the four catalysts were investigated.Among a series of M-N-C catalysts prepared in this paper,Co-N-C catalyst shows the best ORR performance with a half-wave potential of 0.758 V（vs.RHE）in 0.1 M KOH.Electrochemical results show that the order of ORR activity of M-N-C catalysts prepared in this paper is Co-N-C>Mn-N-C>Zn-N-C>Ni-N-C.（2）Performance optimization of metalloporphyrin framework-based Co-N-C catalysts.The ORR performance of the Co-N-C catalyst was optimized by adjusting the amount of cobalt acetate added in the catalyst preparation process,adding graphene（enhancing the dispersion and conductivity of the catalyst）,adjusting the amount of graphene,and calcining the catalyst at low temperature.The optimized catalyst（TH₂-Co-G-300）has an excellent ORR performance with a half-wave potential as high as 0.802 V in 0.1 M KOH（vs.RHE）.