Preparation And Catalytic Oxygen Reduction Performance Of Polymer Metallo-porphyrin Catalysts

Fuel cells have been receiving much attention in recent years due to a potential energy crisis induced by increasing power demands and due to the increasing importance of protecting the environment. However, at its current stage of technology, high costs have hindered the full commercialization of fuel cells. Thus, developing non-precious cathode catalysts to replace expensive Pt-based cathode catalysts has been one of the major approaches to reducing cost. Among many non-precious cathode catalysts discovered, metalloporphyrin complexes have been investigated for several decades since it is a promising candidate for fuel cell oxygen reduction reaction (ORR). A series of metalloporphyrin complexes have been found to exhibit comparable activity in comparison with Pt-based electrocatalysts.This paper in order to solve the above problem and designed Polytetraphenylporphyrin (PTPPM), because the conjugate structure is outspreaded in the plane. Whole polymer molecular constitute a large ring conjugate system, electronic delocalization energy can be lower than monocylic porphyrin. Therefore, its catalytic activity, selectivity and catalytic stability will be better than commen monocylic porphyrin catalysts.Planar Polytetraphenylporphyrin M (Ⅱ) (PTPPM) is synthesized by polymerizing of the 5,10,15,20-tetra(4-carboxyphenyl)-porphyrin M (Ⅱ) (TCPPM). The polymer is characterized systematically by a variety of means such as UV-Vis, FT-IR, XPS and TG. The result of UV-Vis, FT-IR and XPS shows that PTPPFe obtained is stable below 600℃. The active site of PTPPFe/C is FeN4 in phthalocyanine ring. The dynamic thermogravimetric analysis shows that PTPPFe is stable below 600℃. Oxidation resistance of PTPPFe was measured by refluxing in Fenton reagent for 72 h. The UV-Vis spectra indicate that PTPPM is not decomposed and metal is not exfoliated. Polytetraphenylporphyrin M (Ⅱ) (PTPPM) catalysts with composition varying between PTPPFe and active carbon were prepared by vapor deposition method and the catalysts are characterized by XRD. The results show that PTPPM/C can withstand decomposition upon heat treatment at 600℃. The electrocatalytic properties of catalysts have been evaluated by RDE measurements. The best preparation process for the catalysts is heat-treated at 600℃with loading of 6%, whose initial potential for oxygen reduction in O2-saturated H2SO4 is 0.84V. The kinetic parameters confirm that PTPPFe/C catalyzes O2 reduction mainly through a 4-electron pocess. In O2-saturated NaOH solution PTPPM/C catalyst BanPo potential only lower 0.0005 V than Pt/C catalyst.Cyclic voltammetry, linear sweep voltammetry, and chronoamperometry tests were performed in order to observe the catalyst stability in different conditions. Almost no performance deficiency is observed after 10,000 continuous voltammetric cycles,200 potentiometric cycles, and 60 h of chronoamperometry test. The samples are analyzed by UV-Vis spectral. Results show that PTPPM structure without decomposition, metal ions not fall off. PTPPM/C catalysts display significant chemical stability and electrocatalytic stability. These catalysts may be useful for fuel cells.