Materials and Cell Designs
Yttria-doped zirconia (YSZ) remains the most widely used material for the electrolyte in SOFCs because of its sufficient ionic conductivity, chemical stability, and mechanical strength. The only drawback of stabilized ZrO2 is the low ionic conductivity in the lower cell operation temperature regime (below about 750oC). Two solutions that have been tried to resolve this problem are to decrease the thickness of the YSZ electrolyte and to find other acceptors to replace Y. Scandia-doped zirconia has higher conductivity than YSZ but high cost of scandium and detrimental ageing effects in scandiadoped ZrO2 make it less attractive in commercializing SOFCs. Gadolinium- or samarium-doped CeO2 materials possess higher oxide ion conductivity (e.g., Ce0.9Gd0.1O1.95: 0.025 Ω-1•cm-1 at 600°C) compared to zirconia based materials (< 0.005 Ω-1•cm-1). However, CeO2 based materials, under reducing conditions at high temperatures, exhibit significant