Preparation And Study Of Transition Metal Complexe Catalyst For Oxygen Reduction Reaction Of Cathode In Pemfc

In the current area of PEMFC cathode catalyst, Pt-based catalysts still enjoy the best quality and receive more attentions on study. However, Pt-based materials and other noble metals, have limited fuel-cell commercialization due to their high cost and scarcity. Therefore, non-noble metal catalysts known for their high efficiency and low cost ought to be a long-term choice, among which the transition metal complexe catalyst for oxygen reduction corresponding with high activity and selectivity under acidic conditions, has become a hot issue in the worldwide fuel cell communities.(1) In this paper,2,6-Diaminopurine was used as a ligand to prepare Fe-Hdap complexes for the development of a new oxygen reduction reaction (ORR) catalyst. The prepared Fe-Hdap complexes were then heat-treated at600,700,800and900℃to optimize their activity for ORR. It was found that the800℃heat-treatment yielded the most active Fe-Nx/C catalyst. Fe-Nx/C catalyst with several Fe loadings (3,4,5,6,7wt%) were also synthesized and a4.7wt%Fe loading yielded the best catalytic ORR activity. XRD, TG, TEM, XPS and line-scan voltammograms techniques were used to characterize the structural changes in these catalyst after heat-treatment, including the catalyst composition, structure, morphologe, and the electrochemical activity. As observed by XRD, when the heat-treatment temperature or Fe content was too high, Fe3O4could be produced. This would lead to a decrease in ORR activity. XPS analysis revealed that the catalyst surface consists of0.61wt%N (largely pyrrolic-like). The ORR activities of catalysts synthesized using ligands with different structures were studied. The result indicated that the catalyst prepared using the compound containing more pyridinic N as ligand had enhanced activity, and the S element in ligand could improve the activity of Fe-Nx/C catalyst. The stability of This Fe-Nx/C catalyst in the voltage region having ORR kinetic limiting was tested by fixing a electrode potential to record the change in current density with time. The obtained degradation rates for this catalyst was0.0048mA/cm2/h. Further work will attempt to diagnose such a degradation mechanism. Binary FeCo-N catalyst synthesized using the polymer of Hdap as ligand is a promising catalyst having enhanced activity and stability towards the ORR.(2) In this paper, various transition metal complexe catalysts for oxygen reduction were synthesized through ball milling the mixture of tripyridyl triazine (TPTZ) and graphite supported by carbon with immersion method. FT-IR and BET techniques were used to characterize the structural and superficial changes in graphite mixed with TPTZ milled for various times, also the morphologe and composition of the sample milled for12h were analysed by TEM and XPS. The ORR activity of various catalysts were tested and the G2-BM catalysts performance affected by different content of graphite were studied by line-scan voltammograms technique. The result indicated that graphite and TPTZ were not oxidated and only suffered mild structural damages during the ball-milling process. The N atoms didn't dope into graphite lattices to form graphitic nitrogen active sites. With the increase of ball-milling time, BET surface areas of the ball-millded product decreased firstly and then raised, which had a sharp decline during0-3h, and G1-BM catalyst showed the best ORR activity when ball milling for12h. When the graphite accounts for10%of total carbon support, G2-BM catalysts exhibited an excellent quality, as reduced conductivity or specific surface areas would weaken their properties.