Synthesis And Properties Of Non-precious Metal Oxygen Reduction Catalysts Based On Metal Porphyrin Organic Porous Polymers

As a new type of energy conversion and storage device,fuel cells have attracted wide attention from researchers all over the world due to their high efficiency and cleanliness.However,the slow kinetics of the cathodic oxygen reduction reaction（ORR）seriously affects fuel cell efficiency,and the development of an efficient oxygen reduction catalyst is an urgent problem to be solved.Platinum-based catalysts have been proved to be the best catalysts for oxygen reduction catalytic performance,but platinum metal resources are scarce and costly,and they are susceptible to methanol poisoning when used in methanol fuel cells,reducing oxygen reduction catalytic performance and restricting platinum,restricting the large-scale production of base catalysts.Therefore,the development of non-precious metal oxygen reduction catalysts which can replace noble metal platinum with low cost,strong stability and methanol poisoning ability is an effective way to promote the commercialization of fuel cells.Metal nitrogen-doped carbon materials derived from organic porous polymers（POPs）are currently the most promising platinum-based precious metal electrocatalyst replacements.POPs have the advantages of large specific surface area and porosity specific surface area,high chemical stability and thermal stability,and structural adjustment,and the metal nitrogen-doped carbon materials prepared by high temperature pyrolysis can still maintain the porosity of the precursor.The structure,the prepared active sites of the catalyst are generally uniformly distributed on the surface of the carbon layer.In this paper,Fe-POPs,Co-POPs or Fe/Zn-POPs polymers are used as catalytic precursors to prepare metal nitrogen-doped carbon catalytic materials by high-temperature calcination in an inert gas atmosphere,and then oxygen is determined by various physical characterization methods.The structure and active sites of the oxygen reduction catalyst were determined by various physical characterization methods.The electrochemical reduction method was used to study the oxygen reduction catalytic performance of these materials.Meanwhile,the effects of different carbonization temperatures and different central metal species on the oxygen reduction catalytic performance of the prepared metal nitrogen-doped carbon materials were also investigated.The first chapter and the second chapter,briefly summarize the progress of porphyrin structure and its synthesis,and explain the mechanism of cathode oxygen reduction reaction of fuel cell and the current types of oxygen reduction catalyst.The characterization methods used in the experimental part are introduced,and the design ideas of this paper are proposed.In the third chapter,the catalytic precursors based on metal Fe porphyrin polymer were synthesized by using brominated styrene and magnesium powder as raw materials.The carbon-supported Fe-N-C catalyst was prepared by high temperature pyrolysis under high purity nitrogen.The three-electrode system was used to test the ORR performance of the catalyst in 0.1 M KOH and 0.5 M H₂SO₄ electrolytes,respectively.The results show that the Fe-N-C catalyst prepared at 900°C has the best ORR catalytic performance,and the half-wave potential of the polarization curve is E_1/2=0.82 V.In addition,the stability of the material and the resistance to methanol poisoning were evaluated.The chronograph current of the Fe-N-C-900 material after 2400 s of operation was only attenuated by 25%,while the Pt/C catalyst was attenuated by 40%in 1200 s.Therefore,the Fe-N-C catalyst exhibits superior stability to commercial Pt/C.In the fourth chapter,the catalytic precursors of two different central metals were synthesized by Friedel-Craft alkylation reaction,and the carbon-supported CoTCP@Cs and FeTCP@Cs catalysts were prepared by high temperature pyrolysis under high purity nitrogen.According to their ORR catalytic performance test results in 0.1 M KOH electrolyte,the CoTCP@Cs half-wave potential of the catalyst is 20 mV compared with FeTCP@Cs,and both catalysts have superior stability and resistance to methanol poisoning.In the fifth chapter,based on the third chapter experiment,we prepared Zn（II）when preparing the catalytic precursor,and prepared the bimetallic reaction catalyst Fe/Zn@C-900by pyrolysis at 900℃under inert gas atmosphere.According to the electrochemical test results in 0.1 M KOH electrolyte,the presence of Zn can improve the ORR catalytic performance of the material,and still maintain good stability and resistance to methanol poisoning.