In the first part of this study, the characteristics of a La0.5Sr0.5CoO3- cathode are described, including its chemical bulk diffusion coefficient (D-chem), and electrical conductivity relaxation experiments are performed to obtain experimental D-chem measurements of this cathode. The second part of this study describes two methods to improve the single-cell performance of solid oxide fuel cells. One method uses a composite cathode, i.e., a mix of 30wt% electrolyte and 70wt% cathode; the other method uses an electrolyte-infiltrated cathode, i.e., an active ionic-conductive electrolyte with nano-sized particles is deposited onto a porous cathode surface using the infiltration method. In this work, 0.2M Ce0.8Sm0.2O1.9 (SDC)-infiltrated La0.5Sr0.5CoO3- exhibits a maximum peak power density of 1221mW/cm(2) at an operating temperature of 700 degrees C with a thick-film SDC electrolyte (30m), a NiO+ SDC anode (1mm) and a La0.5Sr0.5CoO3- cathode (10m). The enhancement in electrochemical performances using the electrolyte-infiltrated cathode is attributed to the creation of electrolyte/cathode phase boundaries, which considerably increases the number of electrochemical sites available for the oxygen reduction reaction.