Power generation characteristics of a single oxide fuel cell using a c-axis oriented apatite-type (La_0.8Nd_0.2)_9.33Sr_0.37Si_5.7Mg_0.3O_26.065 ceramic electrolyte fabricated using a neodymium magnet

抄録

In solid oxide fuel cells (SOFCs), oxide ion conductors are suitable electrolytes to separate the fuel electrode from the air electrode, and their conductivity has room for improvement. We obtained high oxide ionic conductivity in La_9.7Si_5.7Mg_0.3O_26.25, an oxygen-rich apatite-type lanthanum silicate ceramic involving the partial substitution of Si with Mg in La_9.7Si₆O_26.55. Moreover, partial substitution of La with Sr yielded La_9.33Sr_0.37Si_5.7Mg_0.3O_26.065, which exhibited the highest bulk ionic conductivity (1.9 × 10⁻² S·cm⁻¹ at 500 °C), representing a 1.6-fold increase compared to La_9.7Si₆O_26.55 at 500 °C. To orient La_9.33Sr_0.37Si_5.7Mg_0.3O_26.065 in a magnetic field using a neodymium magnet with c-axis orientation, La was partially replaced by Nd, a trivalent rare earth element with magnetic properties, to prepare (La_0.8Nd_0.2)_9.33Sr_0.37Si_5.7Mg_0.3O_26.065, yielding c-axis oriented products. The ionic conductivity of the bulk parallel to the c-axis (σ//, 5.5 × 10⁻² S·cm⁻¹ at 500 °C) was 1.9 orders of magnitude higher than that of the bulk perpendicular to the c-axis (σ⊥) at 500 °C. An SOFC incorporating (La_0.8Nd_0.2)_9.33Sr_0.37Si_5.7Mg_0.3O_26.065 as the electrolyte [3 % H₂ (Ar balance) | Pt | Sm_0.2Ce_0.8O_1.9 | electrolyte | Sm_0.2Ce_0.8O_1.9 | Pt | air] was fabricated using a 1-mm thick c-axis oriented product. The maximum power outputs at 450, 500, and 550 °C were 29, 60, and 70 mW·cm⁻², respectively.