Development of Layered Perovskites as high-performance cathodes for Intermediate Temperature Solid Oxide Fuel Cells

Abstract

Since the energy resources are much more important in the future, demand of Electrochemical conversion systems have received number of attentions due to their sustainable and eco-friendly properties to prevent drawbacks of fossil-fuel based combustion systems including emission of pollutant, depletion of fossil fuels, and acceleration of global warming. Solid oxide fuel cells (SOFCs) are promising power generation systems because of their high energy conversion efficiency, low pollutant emission, and fuel flexibility. The high operating temperature of primary SOFCs (800–1000 oC), however, leads to crucial problems such as high cost, thermal stress, and incompatibility between the components. In response, numerous research groups have focused on lowering the operating temperature to intermediate temperatures (500–700 oC) to develop reliable SOFC systems. However, the reduced operating temperature results in poor ionic conductivity and low electrocatalytic activity for the oxygen reduction reaction (ORR) at the cathode. Therefore, it is necessary to develop an alternative cathode that has high ionic conductivity and enhanced electrocatalytic activity for the ORR even at intermediate or low temperatures. Co-rich layered perovskites, LnBaCo2O5+, have received widespread attention because of their fast oxygen kinetics and favorable electrochemical properties. Herein, I investigated several approaches to enhance the electrochemical performance of the layered perovskite electrode in intermediate or low operating temperatures. A brief overview of the dissertation follows. At first, the effects of various Ln ions on Sr and Fe co-doped layered perovskites, LnBa0.5Sr0.5Co1.5Fe0.5O5+ (Ln = Pr, Sm, and Gd), are discussed in terms of the oxygen kinetics, crystalline structure, and electrical and electrochemical properties because type of Ln ions is important to determine the characteristics of the electrode material. The crystal structure along with the A and/or B site cations play a significant role in determining the electrical and ionic properties of PrBaCo2O5+ (PBCO) perovskite oxides. Herein, I report the improvement of electrochemical performance by Sc3+ doping into the layered perovskite, PBCO. It is necessary to reduce the sintering temperature of cathode material for Metal-support SOFC. However, reduced sintering temperature would not be optimized to provide enough porous microstructure, resulting in lower electrochemical. In these regards, I modify the microstructure on the screen-printed cathode by the infiltration.