Characteristics of La0.85Sr0.15MnO3-δ powders synthesized by a glycine-nitrate process

The amount of glycine added, i.e. the glycine/oxide molar ratio, k, is optimized for the synthesizing La0.85Sr0.15MnO3-delta (LSM) powders by a glycine-nitrate process. The specific surface area of the resultant LSM powders increased with this ratio, which indicates the deviation of the required glycine from the stoichiometric reaction. The powder is further characterized as a precursor for LSM-SDC (samarium-doped ceria) composite electrodes for solid oxide fuel cells. The electronic conductivity of the LSM-SDC composite increases with increases in the glycine/oxide ratio. In addition, the ratio has an effect on the interfacial polarization resistance of the LSM-SDC electrodes, as determined wit symmetric cells using AC impedance spectroscopy. The lowest resistance is achieved using a LSM powder prepared with 20% more glycine than the stoichiometric requirement (k = 1.2). The activation energies for electrochemical oxygen reduction are about 1.3 eV, when the ratio is below 1.2, and about 1.0 eV, when it exceeds 1.2. The activation energy suggests that oxygen ion transfer is the rate determining process for the LSM-SDC electrode when k >= 1.2, whereas both mass transfer and charge transfer are the rate limiting steps when k < 1.2.