Highly conductive barium zirconate-based carbonate composite electrolytes for intermediate temperature-protonic ceramic fuel cells

摘要

Two-phase composite materials consisting of a BZY matrix phase and a binary eutectic carbonate (Li-0.5Na)_2CO_3 phase are designed in order to promote the densification and ionic conductivity of BaZr_(0.85)Y_(0.15)O_(3-δ) (BZY) proton conductors at intermediate temperature. In the presence of carbonate phase, a considerable change in microstructure for the densification of BZY electrolytes sintered at 670 °C for 4 h is clearly visible in SEM analysis. This sintering effect is due to the formation of molten phase associated with carbonates at low temperature (495 °C) by TG-DTA analysis. The conductivity of composite electrolytes is significantly higher than that of BZY over the entire temperature and atmo sphere range studied by AC impedance and DC four-probe methods. In addition, the change of the carbon ate content in the composite electrolyte presents a great influence on the conductivity. The composite containing 25 wt.% (Li-0.5Na)_2CO_3 shows the highest ionic conductivity of 0.176 S cm~(-1) at 550 °C and lowest activation energy of 0.127 eV in the temperature range of 500-650 °C.