Chemical degradation of La1−xSrxMnO3/Y2O3-stabilized ZrO2 composite cathodes in the presence of current collector pastes

The chemical reactivity of current collector pastes, utilized in electrode performance measurements, were investigated with respect to the solid oxide fuel cell composite cathode, (La85Sr15).98MnO3/8 mol% Y2O3-stabilized ZrO2 (LSM/YSZ). Anode substrate single cells were prepared with Pt or Ag paste current collectors applied to the electrodes. Phase purity of the cathodes before and after sintering the current collectors were examined with powder X-ray diffraction (XRD) and the performance of the cells determined with current-potential measurements. XRD experiments provided evidence that Pt paste, containing a bismuth flux, reacted with the composite cathode at temperatures above 800 °C leading to formation of the pyrochlore phase, La2Zr2O7. Cathodes coated with Ag paste, which did not contain a bismuth flux, showed no sign of chemical degradation. Synthesized Bi-subnitrate and commercial Bi2O3 were shown to have similar chemical reactions with LSM/YSZ powders leading to pyrochlore phase formation. Current-potential experiments on single test cells demonstrated that samples prepared with paste containing bismuth flux had a decrease in initial performance.