BICU(TI)VOX AS A LOW/INTERMEDIATE TEMPERATURE SOFC ELECTROLYTE: ANOTHER LOOK

摘要

Bismuth vanadate (Bi2VO_(5.5-δ)) ceramics, stabilized by partial substitution of V~(5+) with transition metal ions, exhibit high ionic conductivity at temperatures below 500°C. For use as SOFC electrolyte, the ceramic has been dismissed by some due to reports of mixed conduction at higher temperature and reducing or low pO2 atmosphere. The two dimensional conductivity of the oxide vacancies within the layered crystal structure also poses challenges. In the current study, an unique processing scheme was used to produce high density and textured polycrystalline Bi2(V_(0.9)Cu_(0.1))O_(5.5-δ) ceramics. Platelet seeds, produced by molten salt synthesis (MSS), were dispersed within a matrix of fine powders to incite templated grain growth (tgg) during hot forging (HF). Bulk ceramics show high oxide ion conductivity (10~(-1) Ωcm~(-1)) at 500°C, and modest texture gives modest anisotropy. Long term stability of the conductivity at this temperature over a range of pO2 was demonstrated, however at lower temperatures (400°C), larger-grained and textured samples exhibit instability associated with oxygen vacancy ordering. Small grain size in conventionally sintered samples appears to mitigate this instability, as does Ti co-doping. Measured themial expansion (16-20 ppm/°C), also showing small anisotropy in textured samples, may be compatible with metals in SOFC design.