Polypyrrole Constructs “Hybrid Rare Earth Oxide-carbon Layer Core-shell” System For Electrocatalytic Application

For high price and low stability, the commercialization process of fuel cells is hindered by noble metal catalyst seriously. This makes the development and construction of catalyst system with low price and high efficient significant. Hybrid metal oxide has potential application in electrocatalytic reaction of fuel cells. However, the conductivity of rare earth oxide is relatively poor. Consequently, it needs to be modified by carbonized coating. Specially, because of large specific surface area and good electrical conductivity, polypyrrole is considered to be an ideal coated modified material to construct “hybrid rare earth oxide-carbon layer core-shell” system.Hence, the thesis mainly focuses on the construction of “rare earth hybrid oxide-carbon layer core-shell system” through polypyrrole. Firstly, the promoting effect of hybrid metal oxide was investigated to palladium in ethanol oxidation reaction. Subsequently, the “rare earth oxide-carbon layer core-shell” system was constructed by polypyrrole, and the synergistic effect between this system and platinum was also investigated in oxygen reduction reaction（ORR）. Finally, polypyrrole successfully constructed “hybrid rare earth oxide-carbon layer core-shell” system for ORR. In these three parts, the structures of as-prepared catalysts were characterized by physical measurements. And their electrocatalytic performances were also studied by electrochemical test methods. The thesis is consists of three parts as follows: Part I: Hybrid Ni Co Ox oxide promoting Pd nanoparticles for ethanol oxidationPd nanoparticles were supported on as-prepared hybrid Ni Co Ox oxide by polyol method, and the electrocatalytic performance was studied for ethanol oxidation reaction. Physical characterization shows Ni Co Ox is closely adjacent to Pd nanoparticles in Pd-Ni Co Ox/C catalyst, which produces more contact interfaces, leading to strong interactions, in favor of the electrocatalytic effect. And the results of electrochemical measurement indicate that, the introduction of Ni Co Ox would improve the electrocatalytic performance of Pd/C catalyst for ethanol oxidation significantly. Part II: Carbonized polypyrrole coated CeO₂ promoting Pt nanoparticles for oxygen reductionPt-CeO₂@CN was successfully prepared by coating polypyrrole layer and further carbonizing onto CeO₂ obtained through hydrothermal method. In this catalyst, polypyrrole could not only enhance the electrical conductivity of CeO₂, but also improve the stability as Pt nanoparticle support. Compared with Pt/C catalyst, the Pt-CeO₂@CN composed of “rare earth oxide-carbon layer core-shell” system has better electrocatalytic activity for ORR. Meanwhile, it also has better stability. In addition, ORR mechanism was also studied on the catalyst. It is found that Pt-CeO₂@CN catalyst follows a 4e- pathway for ORR Part III: Carbonized polypyrrole coated hybrid CeNiO_x oxide for oxygen reductionBased on the experiments of the first two parts, a series of carbonized polypyrrole coated hybrid CeNiO_x oxide（CeNiO_x@CN-n） catalyst was prepared. The influences of bimetal component and polypyrrole layer thickness on the electrocatalytic performance were explored in the “hybrid rare earth oxide-carbon layer core-shell” system. The results show that when the atomic ratio of Ce : Ni is 1 : 1, the corresponding catalyst presents the best ORR activity. And molar ratio of polypyrrole : oxide = 1 : 1 is the optimal layer thickness. As an ideal non-noble metal catalyst, CeNiO_x@CN-4 catalyst follows a 4e- pathway for ORR. Moreover, it has good electrocatalytic activity and stability. Specially, its anti-methanol poisoning is stronger than Pt/C catalyst. X-ray photoelectron spectroscopy（XPS） displays that graphitization nitrogen plays a dominant role in the CeNiO_x@CN-4 catalyst with “hybrid rare earth oxide-carbon layer core-shell” system, which would benefit its improved electrocatalytic activity.