Solid oxide cells with zirconia/ceria Bi-Layer electrolytes fabricated by reduced temperature firing
Anode-supported solid oxide cells (SOCs) with thin bi-layer Y0.16Zr0.92O2−δ (YSZ)/Gd0.1Ce0.9O1.95 (GDC) electrolytes were prepared by a reduced-temperature (1250 °C) co-firing process enabled by the addition of a Fe2O3 sintering aid. The Fe2O3 amounts in the layers affected the formation of voids at the GDC/YSZ interface; the case with 1 mol% Fe2O3 in the YSZ layer and 2 mol% Fe2O3 in the GDC layer yielded minimal interfacial voids, presumably because of optimized shrinkage matching between the electrolyte layers during co-firing. The best cells yield fuel cell power density at 0.7 V in air and humidified hydrogen of 1.74 W cm−2 (800 °C) and 1.0 W cm−2 (700 °C). Under electrolysis conditions, i.e., air and 50 vol% H2O–50 vol% H2, the best cell area specific resistance is 0.12 Ω cm2 at 800 °C and 0.27 Ω cm2 at 700 °C. This excellent cell performance was explained by a number of factors related to the reduced firing temperature: (1) low electrolyte resistance due to minimization of YSZ/GDC interdiffusion; (2) minimal zirconate phase formation between the YSZ and the La0.6Sr0.4Fe0.8Co0.2O3 (LSFC) cathode because of the dense GDC barrier layer; (3) high three phase boundary density in the Ni–YSZ anode functional layer; and (4) good pore connectivity in the Ni–YSZ support. Preliminary life testing under fuel cell and electrolysis operation shows promising cell stability.