Preparation And Study Of LSM-LSC Composite Cathodes For Solid Oxide Fuel Cell (SOFC)

The state-of-art cathode material for intermediat-temperature solid oxide fuel cell (IT-SOFC) is strontium doped LaMnO3 and LaCoO3 (LSM and LSC). LSM exhibits a high electronic conductivity and good stability, but it exhibits low oxide ion conductivity. The use of LSC with high ionic conductivity and catalytic activity is inhibited due to its high thermal expansion coefficient. The hybrid of cathode and electrolyte was studied to inhibited the sintering of cathode, enlarge the triple phase boundary, and enhance the catalytic activity of the cathode, but the hybrid of two perovskite cathode was not reported. The composites of La₀.8Sr₀.2MnO₃ (LSM) and La₀ 6Sr₀ 4CoO₃ (LSC) substituted for hybrid of electroyte and electrode were first investigated as cathode materials for intermediate temperature solid oxide fuel cells in this paper. This paper will do the following studies for the hybrid of the two cathode materials.1. The compatibility, electrical conductivity, porosity and catalytic properties were investigated by XRD, 4-DC Point, Archimedes method and temperature-programmed reduction (TPR). The XRD results depicted that the LSM-LSC composites remained good structure compatibility after fired at 1200°C. The sintering ratio for composites is inhibited by each other. The shrinkage ratio and porosity of composites electrical rods reached lowest and highest for LSM-LSC40 (containing 40 wt% LSC). The variation tendency of electrical conductivity for composites is similar to the shrinkage ratio of composites with the LSC content. The TPR results showed that the reduction temperature of Mn(IV) to Mn(III) in the composites shifted to lower temperatures with the LSC content, the easier reduction and large peak areas of Mn(IV) and Co(IV) indicated that the catalytic activity of LSM was improved in the hybrid perovskite materials.2. LSM-LSC composites on YSZ electrolyte were investigated. The powerdensity decreases monotonously with the increase of LSC, the polaron resistance increases with the LSC content. The reason is that the composites react vigorously with YSZ with the increase of LSC and form resistive zirconium compounds. The performance of composites on YSZ electrolyte was not enhanced.3. LSM and LSC have good compatibility with CeC>2 doped with Gd2C?3 (GDC). Because the ohmic resistance of composites is almost same on the YSZ/GDC bilayer electroyte at 800°C, this shows GDC interlayer prohibits entirely the reaction between electrode and electrolyte. Comparing to pure LSM and LSC, the performance of composites was enhanced. The highest power densities for composites are highest on bilayer electrolyte when the LSC content is 40 wt%. Polaron resisrances (Rp) decrease with the LSC content, and then increase. At 800°C, the polaron resistance of LSM-LSC60 is lowest for the whole composites. For the cell with a pure LSM cathode, Rpis 0.79 Qcm2; Rp declines to 0.365 fi cm2 for LSM-LSC60, and then increase to 0.89 Q cm2 for pure LSC.