Yttria-stabilized Zirconia Electrolyte Layer Research Articles

Effect of densification processes on the properties of plasma-sprayed YSZ electrolyte coatings for solid oxide fuel cells

Atmospheric plasma spraying (APS) was employed to deposit yttria-stabilized zirconia (YSZ) electrolyte for cermet supported tubular solid oxide fuel cells (SOFCs) to reduce manufacturing cost. A post-spray densification process was conducted for the APS-sprayed YSZ coating in order to achieve a required coating density for gas tightness and improved electrical conductivity. The deposition of the YSZ layer was carried out at ambient atmosphere using commercial ZrO 2–8 wt.% Y 2O 3 powder. The densification of the YSZ coating was attained through impregnating yttrium and zirconium nitrate solutions into the porous coating, followed by thermal decomposition of nitrates within the pores of the coating through annealing treatment. The effects of impregnation number on gas permeability and electrical conductivity of the YSZ electrolyte have been examined. It was found that the gas permeability of the YSZ electrolyte layer after the densification treatment reaches a level of 2×10 −7 cm 4 gf −1 s −1, which is a necessary value for practical operation of SOFCs. The test cell yielded an open circuit voltage of 1.0 V at 930 °C. Furthermore, the anisotropy of the electrical conductivity of the YSZ coating is clearly elucidated by comparing the present result to the reported data. The electrical conductivity of the as-sprayed YSZ coating showed a value of 0.53 S m −1 from the through-thickness direction at 900 °C. The post-densification treatment using nitrate solution improved the electrical conductivity of the YSZ layer by ∼30%.

Performance of YSZ electrolyte layer deposited by atmospheric plasma spraying for cermet-supported tubular SOFC

Yttria-stabilized zirconia (YSZ) was deposited by plasma spraying to develop a cost-effective processing method for the fabrication of electrolyte layer in solid oxide fuel cells (SOFCs). A densification process to plasma-sprayed YSZ coating was conducted with the aim of achieving a dense coating of necessary gas-tightness and an improved ionic conductivity. The densification of ZrO 2–4.5 mol% Y 2O 3 electrolyte, which was produced by atmospheric plasma spray, was performed by impregnating yttrium and zirconium nitrate solution into the coating followed by heat-treatment. The results show that the YSZ layer of the gas permeability comparable to that of fully sintered one can be formed through plasma spraying followed by impregnation densification. The test cell yielded an OCV of 1.04 V and a maximum output power density of 101 mW/cm 2 at 930°C. Those results show that the combination of plasma spraying with post-impregnation is a feasible process to fabricate YSZ electrolyte layer used in SOFC.

High-temperature mechanical properties of anode-supported bilayers

Abstract Mechanical properties of a porous substrate of 40 vol.% Ni–60 vol.% yttria-stabilized zirconia (YSZ), a Ni–YSZ functional layer, and a YSZ electrolyte layer were measured in compression from 1000 to 1200 °C. The anode-supported bilayer is brittle for temperatures

Reactions of (La,Ca)CrO3 sealants in yttria-stabilized zirconia-(La,Ca)CrO3 planar solid oxide fuel cell (SOFC) stacks

Flat yttria-stabilized zirconia (YSZ) films were prepared by the doctor blade technique. The joining of the solid oxide fuel cell (SOFC) stack was carried out using La0.7Ca0.3 + xCrO3 (x = 0.03 and 0.06) green films as sealants between the YSZ electrolyte layer and the La0.8Ca0.2 + yCrO3 (y = 0.02 and 0.03) separator. Reactions between the component layers of the stack were examined in terms of elemental diffusion. The YSZ film produced by the doctor blade technique yields about the same electrical conductivity as the YSZ pellet. During the joining, the Ca in the sealant diffused and dissolved into YSZ and La0.8Ca0.23CrO3, and the sealants reacted with YSZ to form CaZrO3 phase at the interface. The joining was accomplished by the formation of thick CaZrO3 layers at the interface.