Electrochemical behavior of Ba0.5Sr0.5Co0.2-xZnxFe0.8O3-delta (X=0-0.2) perovskite oxides for the cathode of solid oxide fuel cells

Abstract

Zinc-doped barium strontium cobalt ferrite (Ba0.5Sr0.5Co0.2-xZnxFe0.8O3-delta (BSCZF), x = 0, 0.05, 0.1, 0.15, 0.2) powders with various proportions of zinc were prepared using the ethylenediamine tetraacetic acid (EDTA)-citrate method with repeated ball-milling and calcining. They were then evaluated as cathode materials for solid oxide fuel cells at intermediate temperatures (IT-SOFCs) using XRD, H-2-TPR, SEM, and electrochemical tests. By varying the zinc doping (x) from zero to 0.2 (as a substitution for cobalt which ranged from zero to 100%), it was found that the lowest doping of 0.05 (BSCZF05) resulted in the highest electrical conductivity of 30.7 S cm(-1) at 500 degrees C. The polarization resistances of BSCZFO5 sintered at 950 degrees C were 0.15 Omega cm(2), 0.28 cm(2) and 0.59 cm(2) at 700 degrees C, 650 degrees C and 600 degrees C, respectively. The resistance decreased further by about 30% when Sm0.2Ce0.8O2-delta (SDC) electrolyte particles were incorporated and the sintering temperature was increased to 1000 degrees C. Compared to BSCF without zinc, BSCZF experienced the lowest decrease in electrochemical properties when the sintering temperature was increased from 950 degrees C to 1000 degrees C. This decrease was due to an increase in thermal stability and a minimization in the loss of some cobalt cations without a decrease in the electrical conductivity. Using a composite cathode of BSCZFO5 and 30 wt.% of SDC, button cells composed of an Ni-SDC support with a 30 mu m dense SDC membrane exhibited a maximum power density of 605 mW cm(-2) at 700 degrees C.