Preparation Of The Metal Organic Complexes Based Catalysts And Their Oxygen Reduction/Evolution Performances

Li-air battery, which is environment friendly, light-weight and has high theoretical energy density, has been considered as a promising secondary battery. However, the oxygen reduction reaction (ORR) occurring during discharging process and the oxygen evolution reaction (OER) during charging process are kinetically sluggish, leading to high overvoltage and low performance of the battery. Therefore, it is needed to develop catalysts with low price and excellent property to accelerate the ORR/OER, thus improving the performance and promoting the commercialization of Li-air battery. In recent years, metal-organic complexes as a kind of excellent catalytic materials have aroused great attention in the field of electrocatalysis because of their high specific surface areas, tunable pore structures and flexibility to be easily functionalized. In this dissertation, we prepared several metal-organic complex catalysts, such as [C3H5N2]2[Co(H2O)6][Co(BTC)2·4H2O], M-PTA-4,4-bpy, Prussian blue analogues, and their derivatives, and studied their structures and performance toward ORR/OER.The catalyst triclinic purple crystal [C3H5N2]2[Co(H2O)6][Co(BTC)2-4H2O] was prepared through a hydrothermal method by using cobaltous acetate as precursors and using imidazole and trimesic acid as organic ligands. The catalyst shows good crystalline structures and unique parallel ?-? structures. The distance of the adjacent two layers is found to be 3.0727 A. In an alkaline electrolyte, the catalyst shows excellent bifunctional catalytic activities towards ORR/OER. At 0.8 V (vs. Ag/AgCl), its OER current density is 24.16 mA·cm-2, its ORR half-wave potential is -0.31 V, and its ORR current retention after 15800 s stability test is about 80%.Hydrothermal synthesis was used to prepare eight different samples, which can be mainly divided into two classes, by using metal acetate as precursors, and using 1,4-dicarboxybenzene (PTA), tetrachloroterephthalic acid (H2BDCCl4) and 4,4'-Bipyridine (4,4-bpy) as organic ligands. The catalysts not only show good crystallization, but also possess abundant pores. Co-PTA-4,4-bpy shows the best bifunctional catalytic activities towards ORR/OER among the M-PTA-4,4bpy samples. For the Co-PTA-4,4-bpy sample, at 0.8 V (vs. Ag/AgCl), the OER current density is 17.50 mA·cm-2, and the ORR half-wave potential is -0.30 V. Co-BDCCl4-4,4-bpy shows the best bifunctional catalytic activities towards ORR/OER among the M-BDCCl4-4,4-bpy samples. For Co-BDCCl4-4,4-bpy, at 0.8 V (vs. Ag/AgCl), the OER current density is 89.04 mA·cm-2, and the ORR half-wave potential is -0.31 V.Two different kinds of Prussian blue analogues were prepared by using cobalt nitrate as precursors and using potassium hexacyanocobaltate (?) as organic ligands. Then a series of Prussian blue analogous-derived catalysts were obtained through pyrolysis in inert or oxygen environment. The OER/ORR catalytic activities of Prussian blue analogous-derived catalysts treated in oxygen treatment were decreased compared with the pristine samples. While the OER/ORR catalytic activities of the catalysts treated in inert environment were increased significantly. Especially a Prussian blue analogue (Co)-derived catalyst treated in nitrogen at 500 ? has the best ORR/OER catalytic performance. At 0.8 V (vs. Ag/AgCl), its OER current density of OER is 62.70 mA·cm-2, its ORR half-wave potential is -0.16 V, and its bifunctional stability is excellent. The surface Co2+ and Co3+ species on the catalyst may play a key role in the catalytic performance of the catalyst.