Preparation of BiMeVO_x (Me = Cu, Ti, Zr, Nb, Ta) compounds as solid electrolyte and behavior of their oxygen concentration cells

A group of complex metal oxides, BiMeVO_x, which a fraction (x) of V in Bi₄V₂O₁₁ is replaced by foreign metal, has been reported to be oxide-ionic conductors. The various kinds of oxides in this group, Me = Cu (x = 0.1), Zr (x = 0.1), Ti (x = 0.4), Nb (x = 0.15) and Ta (x = 0.15), were investigated for electrochemical characterization based on oxygen concentration battery. The powders of BiMeVO_x, their structural phases to the high temperature phase (γ) of Bi ₄V₂O₁₁, were obtained by calcining at 700-850 °C. Each sample was compacted into a disk, and installed into an oxygen concentration cell. The oxygen concentration cells using the resulting disks of BiMeVO_x, especially Me = Cu, were found to work as an oxygen sensor fairly well at 700 °C: the number of reaction electrons (n) associated with the reduction of O₂ was close to the theoretical one (4). With lowering operating temperature, however, the O₂-responding properties degraded rather quickly: it was far larger at 500 °C. Such degradation was confirmed to be owing to decrease the rate of electrode reactions through the measurement of Faraday efficiency of oxygen pumping current. As a result, the performances of the cells were found to depend very much on the kinds of electrode materials. The use of a perovskite-type oxide, La_0.6Sr _0.4Co_0.8Fe_0.2O₃, instead of Pt as a electrode was found to enable the cell to work at 400 °C and above.