A Study On Perovskite Bi-functional Oxygen Electrodes

In this dissertation, the electrochemical performances of perovskite bi-functional oxygen electrodes are studied. A series of novel nano-level perovskite electro-catalysts are prepared by doping on B and A site of LaNiO3, a metallic perovskite oxide, and further applied in the novel and very promising air-metal hydride secondary batteries. By means of the physical and chemical examinations and electrochemical methods, the optimization of sol-gel preparation method of catalysts and process of bi-functional oxygen electrodes, the effect on catalytic activities of perovskite electro-catalysts with different doped elements, site and ratio, and the cycle life and performance of the oxygen electrodes by using them in rechargeable air-metal hydride batteries are particularly researched. A series of nano-level La1-xSrxNi1-yCo(Fe)yO3 crystals are synthesized by sol-gel method which is confirmed by TG-DAT, XRD, particle size distribution and SEM analysis. The component recipe of bi-functional oxygen electrodes is optimized with examining and comparing the electrochemical performances. XPS, polarization and CV curves examination, electrochemical impedance spectroscopy, decomposition reaction rate of H2O2 catalyzed by perovskite catalysts, and mathematic simulation of polarization curves are used to research the electro-catalytic activities on oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) of perovskite bi-functional oxygen electrodes. It can be concluded that partial displacement of Ni with Fe and Co in LaNiO3 can largely enhance the activities and they exceed the activities of LaNiO3 and La0.6Ca0.4CoO3, a popular good catalysts. LaNi0.8Co0.2O3 and LaNi0.8Fe0.2O3 show the best performance. The former shows a higher activity and the latter shows a better stability. Further doping Sr2+ ions on A site of LaNi0.8Co0.2O3 and LaNi0.8Fe0.2O3 could impair the activities because the increase of ordering level of oxygen vacancy result in the increase of electrode resistance. The polarization resistance of oxygen electrode is mainly caused by the slow Nernstian diffusion of O2 and HO2-and charge transfer resistance. The hypothesis of electro-catalytic mechanism is also suggested. The bi-functional oxygen electrodes used LaNi0.8Fe0.2O3 and LaNi0.8Co0.2O3 catalysts are examined in air-metal hydride rechargeable batteries. Both oxygen electrodes show good performances during 152h charge and discharge cycles. The power densities of batteries using the electro-catalysts mentioned above respectively exceed the power density of batteries using La0.6Ca0.4CoO3. The battery using LaNi0.8Co0.2O3 has a better performance and the battery using LaNi0.8Fe0.2O3 has a smaller capacity decay.