Electrochemical Performance of Cobalt-Free Nb and Ta Co-Doped Perovskite Cathodes for Intermediate-Temperature Solid Oxide Fuel Cells

摘要

This work characterizes a series of Ta and Nb co-doped cobalt-free perovskite oxides with the compositions of SrNb0.2-xTaxFe0.8 O3-delta (x=0, 0.05, 0.1, 0.15, and 0.2) for intermediate-temperature solid oxide fuel cell (IT-SOFC) applications. Their electronic conductivities displayed semiconducting behavior (i. e. increase with temperature rise) between 300 and 500 degrees C and metallic behavior (i.e. decrease with temperature rise) from 500 to 900 degrees C. SrNb0.1Ta0.1Fe0.8O3-delta provided the highest electrical conductivity that reaches 300 S cm(-1) at 500 degrees C. The thermal expansion coefficients for SrNb0.2-xTaxFe0.8O3-delta were lower than those reported for cobalt-containing perovskite cathodes. They varied from 12.83 x 10(-6) to 16.31 x 10(-6) K-1 between 30 and 810 degrees C. Among the five tested cathodes, SrNb0.1Ta0.1Fe0.8O3-delta exhibited the lowest area-specific resistance between 550 and 750 degrees C, with a minimum of 0.046 Wcm(2) at 750 degrees C, when tested in its symmetric cell configuration of cathode vertical bar Sm0.2Ce0.8O1.9 (SDC)vertical bar cathode. A peak power density of 1223 mWcm(-2) was achieved on a SrNb0.1Ta0.1Fe0.8O3-delta vertical bar SDC vertical bar yttria-stabilized zirconia (YSZ) vertical bar Ni-YSZ anode-supported fuel cell at 700 degrees C. This work highlights the opportunity to create new perovskite cathode compositions with improved electrochemical performance through a co-doping strategy.