Physical and Electrochemical Characterization of La0.25Sr0.25Ca0.40Ti0.95Ni0.05-xSnxO3–δ (x=0...0.05) Reversible Solid Oxide Cell Fuel Electrode

Abstract

Redox stability and sulfur- or carbon tolerance of solid oxide fuel cell electrodes are deeply defined by the chemical composition of the materials 1-3. Therefore, much effort is invested in finding more chemically stable and electrochemically active materials. Generally, mixed ionic electronic conductor (MIEC) fuel electrodes offer better stability at the expense of lower electrocatalytic activity towards H2 and CO oxidation, whereas, exsolution of catalytically active nanoparticles may help increase the latter 4. Recently, excellent electrocatalytic performance has been demonstrated for lanthanum and calcium doped strontium titanate based MIEC materials in fuel cell and electrolysis modes 5,6.In this study, chemical stability and electrochemical performance of tin and nickel co-doped strontium titanate MIEC electrode materials (La0.25Sr0.25CaxTi0.9Ni0.50-ySnyO3–δ) were studied. Preliminary characterization included chemical stability studies followed by electrochemical characterization of most stable materials.All studied fuel electrode materials were synthesized using standard nitrate combustion method. All the single cells were prepared using commercially available 250 μm thick Zr0.89Sc0.10Ce0.01O2- d (10Sc1CeSZ, Kerafol) electrolyte support and La0.6Sr0.4CoO3- δ (LSC) oxygen electrode. Fuel and oxygen electrodes were sintered for 5 hours at 950°C and 900°C, respectively. Scanning electron microscopy, X-ray diffraction, FIB-TOF-SIMS and ICP-MS methods were used to characterize materials. Electrochemical characterization was carried out at temperature range from 700 to 850 °C in various H2O, CO2, H2 and Ar inlet concentrations.The chemical stability was greatly influenced by the A-site deficiency and B-site composition of the material as confirmed by comparing the FIB-TOF-SIMS data of as-synthesized and 100 hours reduced fuel electrode materials. Furthermore, as expected, a variation in Ni and Sn content resulted in large variations in studied single cell’s performances. Finally, the stability to the sulphur impurities in fuel electrode gas was investigated for some studied materials.