Performance Enhancement of Intermediate Temperature SOFC Cathode by Nano-Composite Coating

The La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF) is categorized as a mixed ionic-electronic conducting oxide has found significant attention as cathode material in solid oxide fuel cells (SOFCs) operating at intermediate temperatures, 500-850 degrees C. The performance of LSCF electrode is limited by the oxygen ion transport process at the surface, which is the rate determining step of oxygen reduction reaction. To enhance the oxygen surface exchange process of LSCF electrode, a nano-composite electrolyte is introduced at the surface, which substantially improves the electrochemical performance. The electrical conductivity relaxation technique (ECR) has been used to study the oxygen surface exchange kinetics of bare LSCF and coated with a mixture of Ce0.8Sm0.2O2-delta (SDC) and ZrO2 center dot Y2O3 (Yttria-stabilized zirconia YSZ) nano-powders in three different weight ratios, SDC:YSZ = 0.5:1, 1:1, 1:0.5. The chemical oxygen surface exchange coefficient kchem of surface modified specimens were derived with a one-parameter fitting process. The results show that the oxygen surface exchange kinetics of LSCF is affected by the SDC-YSZ coating and the average kchem values of SDC-YSZ coated LSCF increases by a factor 2 to 8 from 650 to 850 degrees C, respectively. It has been concluded that the high ionic conductive oxide coating improves the oxygen surface exchange kinetics of underlying LSCF mixed conducting oxide and consequently enhances the performance of electrochemical device such as solid oxide fuel cell.