Study of cobalt-based perovskite cathodes for intermediate temperature-operating solid oxide fuel cell

Abstract

This thesis describes the effect of Sr substitution on the structure and properties of complex perovskite, and layered perovskite to apply cathode materials for Intermediate Temperature-operating Solid Oxide Fuel Cell (IT-SOFC). Significantly, Sr doped layered perovskites showing as $LnBa_{0.5}Sr_{0.5}Co_2O_{5+δ}$ were studied to determine the factors that drive cathode material for IT-SOFC. For complex perovskite as $Ln_{1-x}Sr_xCoO_3$ (Ln: Pr, Nd, Sm and Gd), the X-ray photoelectron spectroscopy (XPS) analysis shows surface characteristics composed of oxygen lattice and chemisorbed site on the surface of the complex perovskite oxide. These properties are correlated with cathodic reaction in cathode material for IT-SOFC. The Co state and inter-atomic distance properties in complex perovskite are analyzed by using Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES) experiments in order to investigate the energy state of complex perovskite. According to the surface and electronic analysis, these investigations can be related with cathode performance in Co and Sr doped complex perovskite. The electrochemical properties of complex perovskite oxides are investigated for cathode materials of IT-SOFC. For $Ln_{1-x}Sr_xCoO_3$ oxides, substitution of 0.5 mole in A-site of complex perovskite shows the lowest area specific resistance(ASR). Layered perovskite oxides showing as the chemical form of $LnBaCo_2O_{5+δ}$ have been investigated in the field of colossal magneto resistance (CMR) due to the high oxygen diffusivity and superior surface kinetics. In this thesis, the electrochemical analysis of layered perovskite oxide has been focused on the application of cathode materials in IT-SOFC. Especially, the cathode polarization of Sr doped layered perovskite oxide, $LnBa_{0.5}Sr_{0.5}Co_2O_{5+δ}$, has been investigated in order to show the impact of Sr substitution in layered perovskite. The ASR from the form of composite...