Low temperature ac electric field-assisted sintering of unitary anode-supported solid oxide fuel cell

Abstract

Unitary planar solid oxide fuel cells (cathode La0.84Sr0.16MnO3 thin film/solid electrolyte ZrO2:8 mol% Y2O3 thin film/anode ZrO2:8 mol% Y2O3/NiO 55/45 vol.% 5.0 x 5.0 x 1.5 mm3 thick pellet) were prepared by electric field-assisted sintering. The application of multiple 300 V.cm-1 pulses at 1 kHz with 1-5 A limiting current at 1100 oC for 10 min produced single SOFC devices with dense electrolyte and porous anode and cathode. The electrical conductivity of the cells, measured at 590 oC by the impedance spectroscopy technique in the 5 Hz-13 MHz range in a HP4192A impedance analyzer, showed the increase in the electrical conductivity in comparison with the conventionally sintered cell. The microstructure of cross sections of the cells was observed in a scanning electron microscope. The images of the electric field-assisted sintered cells showed dense electrolyte and porous anode and cathode. Joule heating, provoked by the AC electric current pulses resulting from the application of the AC voltage, promoted NiO reduction at the anode, detected by EDX analysis in its intergranular region. L/L0 dilatometry shrinkage curves, J x t electric current pulses, Z'() x Z''() impedance plots and scanning electron microscopy micrographs show how anode-electrolyte-cathode ceramic cells can be sintered at temperatures lower than the usually required.