Sintering composite electrolytes of yttria-doped bismuth oxide and yttria-stabilized zirconia for solid oxide fuel cells

Solid oxide fuel cell (SOFC) with high conversion efficiency has drawn great attention for a sustainable future. Its electrolyte, typically yttria-stabilized zirconia (YSZ), is usually sintered above 1400 °C with commercially available powder materials. To lower the sintering temperature, yttria-doped bismuth oxide (YDB) is investigated in this work as an additive to form composite electrolytes. Dilatometric analysis reveals that the temperature corresponding to the maximum shrinkage rate is decreased from 1260 to 870 °C by YDB. Meanwhile, adding YDB results in the formation of poor conductive second phase monoclinic zirconia (m-ZrO₂), especially when YDB content reaches 3 mol%. Thus, total conductivity decreases and then increases with YDB content. It is noted that the grain boundary conductivity is substantially improved, which is caused by bismuth enrichment at the grain boundary region of the dense composite electrolyte.