An FeNbO₄-based oxide anode for a solid oxide fuel cell (SOFC)

The advantage of n-type semiconductor for an anode of solid oxide fuel cells (SOFCs) lies in its higher electronic conductivity in reducing atmosphere than in air. In this study, n-type FeNbO₄-based oxides that can be reduced at temperatures below 700 °C for a conductivity above 1 S cm⁻¹ are explored as anode materials for a ceria-based SOFC utilizing liquefied-petroleum-gas (LPG) fuel apart from pure H₂. Fe_0.8Nb_1.2O₄ with 20 at.% Fe deficiency was founded in the sample sintered at 1250 °C. The structure stability of FeNbO₄ under reducing atmosphere can be improved by its solid solution with a less-reducible TiO₂ that also stabilizes the high-temperature α-PbO₂ type structure with mixed Fe³⁺ and Nb⁵⁺ cation. In particular, a full cell employing Ti_0.36(Fe_0.985Nb_1.015)_0.84O₄, a stable and electrically conductive (1 S cm⁻¹) oxide in 5% H₂, as anode shows a powder density of 180 mW cm⁻² at 700 °C if 0.5 wt% Pd is impregnated to increase the electrocatalysis and the electric loss is mostly from the electrolyte. The oxide anode showed a degradation (20% during the 5–26 h aging) and the carbon deposition is slight after 5-h operation under an LPG fuel.