Solid oxide fuel cells with YSZ-BNO Bi-layer electrolyte film deposited by magnetron sputtering

Bi-layer electrolyte films of Zr0.84Y0.16O1.92 (YSZ)- 0.79Bi2O3-0.21Nb2O5 (BNO) were deposited by RF magnetron sputtering on NiO-SDC anode substrates. The stoichiometry of the BNO electrolyte film was found strongly dependent on the ratio of Ar and O2 during sputtering, and the BNO film deposited at a mixture of 31 sccm Ar and 7 sccm O2 appeared to be the closest to the target composition. When deposited at 300 °C and subsequently annealed at 700 °C, the BNO electrolyte emerged to be crack free and dense with some scattering closed pores. The XRD patterns of the film are indexed to the cubic Fm 3¯ m structure of Bi3NbO7. The as-deposited film was well-crystalline and consisted of fine grains and random orientation microstructures. For electrolyte thicknesses of approximately 4.0 μm YSZ and 1.5 μm BNO layers, the open circuit voltage (OCV) and the maximum power density of the single cell with Ag cathode read respectively 0.94 V and 10 mW/cm2 at 600 °C. These OCV values are lower than the expected theoretical value due to the high partial electronic conductivity.