Electrical properties of (La_(0.9)Ca_(0.1))(Co_(1-x)Ni_x)O_(3-?) cathode materials for SOFCs

摘要

Modified perovskite ceramics (La_(0.9)Ca_(0.1))(Co_(1-x)Ni_x)O_(3-?) (x = 0-0.3) cathodes for solid oxide fuel cells (SOFCs) were synthesized by solid state reaction. The lattice parameters, electrical conductivity, activation energy, and microstructures of these specimens were investigated systematically in this study. The results exhibited that all specimens are rhombohedron structures and their tolerance factors were greater than 0.97, indicating that the perovskite was not distorted by Ni~(2+) cation substitution for the B site of (La_(0.9)Ca_(0.1))(Co_(1-x)Ni_x)O_(3-?). The microstructures of the (La_(0.9)Ca_(0.1))(Co_(1-x)Ni_x)O_(3-?) specimens showed good densification, and were well-sintered, with few pores. The electrical conductivity behavior conformed to the nature of a semiconductor, for all specimens. As x = 0.1, the electrical conductivity reached the maximum value of 750.3 S/cm at 800 °C, and the activation energy calculated from the Arrhenius plot of the electrical conductivity versus the reciprocal of temperature is 7.1 kJ/ inol. The novelty of this study is its introduction of the concept of defect chemistry to explain the relationship between compensation mechanisms and electrical conductivity. The information gleaned regarding charge compensation mechanisms and defect formation may be valuable for a better understanding of the cathode of (La_(0.9)Ca_(0.1))(Co_(1-x)Ni_x)O_(3-?) ceramics used for SOFCs. Moreover, the information about oxygen content versus temperature is useful for expressing the relationship between electrical conductivity and composition. Therefore, we also used thermogravimetric analysis combined with the room-temperature oxygen content which was determined by iodometric titration to investigate the oxygen content from room temperature to high temperature, in air. Based on the experimental results, the (La_(0.9)Ca_(0.1))(Co_(1-x)Ni_x)O_(3-?) specimen shows high electrical conductivity. Consequently, it is identified as a promising candidate for cathode SOFC applications.