Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3-δ) + LaCoO_3 composite cathode for Sm_(0.2)Ce_(0.8)O_(1.9)-electrolyte based intermediate-temperature solid-oxide fuel cells

摘要

A novel Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3-δ) + LaCoO_3 (BSCF + LC) composite oxide was investigated for the potential application as a cathode for intermediate-temperature solid-oxide fuel cells based on a Sm_(0.2)Ce_(0.8)O_(1.9) (SDC) electrolyte. The LC oxide was added to BSCF cathode in order to improve its electrical conductivity. X-ray diffraction examination demonstrated that the solid-state reaction between LC and BSCF phases occurred at temperatures above 950℃ and formed the final product with the composition: La_(0.316)Ba_(0.342)Sr_(0.342)Co_(0.863)Fe_(0.137)O_(3-δ) at 1100℃. The inter-diffusion between BSCF and LC was identified by the environmental scanning electron microscopy and energy dispersive X-ray examination. The electrical conductivity of the BSCF + LC composite oxide increased with increasing calcination temperature, and reached a maximum value of ～ 300 S cm~(-1) at a calcination temperature of 1050℃, while the electrical conductivity of the pure BSCF was only ～ 40 S cm~(-1). The improved conductivity resulted in attractive cathode performance. An area-specific resistance as low as 0.21 Ω cm~2 was achieved at 600℃ for the BSCF (70 vol.%) + LC (30 vol.%) composite cathode calcined at 950℃ for 5h. Peak power densities as high as ～ 700mWcm~(-2) at 650℃ and ～525 mW cm~(-2) at 600℃ were reached for the thin-film fuel cells with the optimized cathode composition and calcination temperatures.