Tailoring the surface of perovskite oxide for enhanced oxygen exchange kinetics

Nanocrystalline perovskite structured La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) considered as a promising cathode material for solid oxide fuel cells (SOFCs). The performance of LSCF electrode is limited by the transport of oxygen ions at the oxide surface, which is the rate determining step of oxygen reduction reaction (ORR). To enhance the oxygen surface exchange process of LSCF electrode, a composite electrolyte is introduced at the surface, which substantially improves the electrochemical performance. The electrical conductivity relaxation (ECR) technique is used to study the surface exchange kinetics of bare LSCF and coated with a mixture of Ce_0.8Sm_0.2O_2-δ (SDC) and La₂Mo₂O₉ (LMO) nano-powders in three different weight ratios, SDC:LMO = 0.5:1, 1:1, 1:0.5. The oxygen surface exchange coefficient (kchem) of surface modified specimens were derived by assuming constant oxygen diffusion coefficient (D_chem). The results show that the kchem of LSCF is predominantly affected by the surface coating of SDC-LMO and the average kchem values of SDC-LMO coated LSCF increases by a factor 5 to 10 from 650 °C to 850 °C, respectively. It has been concluded that the high ionic conductive oxide coating improves the surface exchange kinetics of underlying LSCF mixed conducting oxide and consequently enhances the performance of electrochemical devices such as SOFC and oxygen separating membranes.