Low-Polarization Composite Cathodes Based on Nanocatalysts and Oxygen Ion Conductor for Solid Oxide Fuel Cell (SOFC) Applications

SOFCs have shown apparent advantages over other types of fuel cells, including relatively less expensive materials, tolerance to impurities containing in the fuel, long life and high efficiency. However, low-temperature operation also slows down the electrode kinetics and induces large interfacial polarization resistances. Moreover, the cathode polarization is the main obstacle to achieving high power densities at temperatures lower than 700°C.

An ideal cathode may be made of highly conducting ionic and electronic conductor with desired nanostructure. Thus, the objective of this work is to develop high performance composite cathode consisting of an oxygen ion conductor and metallic and/or nonmetallic catalysts with nanostrcutrures. A one-step synthesis method is developed to form colloidal Ag nanocatalysts by reducing silver ions with sodium borohydride (NaBH₄) using adequate capping and stabilizing agents. As a result, a composite cathode made of Bi₂O₃-based ionic conductor and well-dispersed Ag nanocatalysts is obtained at the temperature as high as 600 °C. The commonly used composite cathode, LSM-YSZ, is also investigated for comparison. The crystal structure, microstructure, and electrical/electrochemical properties of the developed composite cathode are investigated using XRD, FESEM, TEM, and impedance spectroscopy.