Low-Temperature Planar Oxygen Generator with (Bi_1.50Y_0.50)_0.98Zr_0.04O_3+δ/Bi_1.71Nb_0.25Ba_0.04O_3+δ Dual-Layer Electrolyte Membrane

In this study, a low-temperature planar solid electrolyte oxygen generator (SEOG) based on a (Bi_1.50Y_0.50)_0.98Zr_0.04O_3+δ (BYO)/Bi_1.71Nb_0.25Ba_0.04O_3+δ (BBNO) dual-layer electrolyte membrane was developed. The SEOG device consisted of a Ag (10 µm)/BBNO (13 µm)/BYO (710 µm)/BBNO (13 µm)/Ag (10 µm) cell sandwiched between a pair of modular planar SUS 316 interconnects with a web-type gas flow channel using a ZnO-SiO₂-Al₂O₃ glass sealant. The BYO layer had high oxygen-ion conductivity at low temperatures, while the BBNO layer provided good adhesion to the high-fire Ag electrode. The leakage value of the SEOG device tested at an operating temperature of 550°C was less than 0.005 (standard cubic centimeters per minute) sccm/cm. The device had excellent hermetic performance and mechanical integrity, thereby verifying the feasibility of the SEOG configuration. The oxygen flux produced by the SEOG device linearly increased with current density, reaching 0.72 cm/min at a current density of 0.20 A/cm², slightly deviated from the Faraday relation at 0.25 A/cm², and then began to level off beyond 0.25 A/cm². The Faradaic efficiency of the device was 96.3% at up to 0.20 A/cm² and dropped rapidly to 66.6% at 0.37 A/cm². The rapid degradation of the oxygen production at high current density was caused by the reduction of the BYO/BBNO electrolyte and the concentration polarization at the electrodes. As the applied voltage driving the current density was higher than the BYO/BBNO decomposition voltage of 0.58 V at 550°C, it triggered the instability of the Ag/BBNO/BYO/BBNO/Ag cell and thus, that of the SEOG device.