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In LaNbO 4 , Sm, Gd and Yb were investigated as substitutes to enhance its ion conductivity, for its application in solid oxide fuel cell. La 0.9 M 0.1 NbO 4 (M = Sm, Gd, Yb) was prepared via a solid–state reaction route and single phase was attained by calcining the constituent oxides at 1200 °C for 5 h. The total conductivity of LaNbO 4 was increased by partly replaced La with Sm, Gd and Yb, due to the muti-valences of the substitutions. The highest conductivity (1.76 × 10 −4 S cm −1 ) was achieved for La 0.9 Sm 0.1 NbO 4 at 800 °C in wet air, more than one order higher compared to that of LaNbO 4 . The introduction of Sm, Gd or Yb also slightly increased the ion transport number of LaNbO 4 , indicating that the increase of the total conductivity was mainly contributed by the enhanced ion conductivity, which was beneficial for its application as a pure ion conductor. [ABSTRACT FROM AUTHOR]

Hydration properties and electrical characteristics of the hightemperature proton conductor La27(W0.85Nb0.15)5O55.5-δ are investigated by means of thermogravimetry, impedance spectroscopy, and the electromotive force (EMF) method as a function of temperature, water vapor, and oxygen partial pressures, as well as isotope exchange measurements in order to elucidate the mechanism and thermodynamics of protons formation and transport. The highest proton conductivity, 1.3 3 10-3 S/cm, is achieved at 700°C in wet O2. Proton selfdiffusion coefficients are estimated from thermogravimetric measurements of hydration and conductivity data. Comparison of the conductivity characteristics between nominally pure and Nb-substituted materials reveals that the ionic conductivity increases and the activation energy decreases with Nb doping. These differences are discussed to reflect changes in the structure promoting ionic transport rather than changing the concentration of defects to any large extent. [ABSTRACT FROM AUTHOR]

Hydration properties and electrical characteristics of the hightemperature proton conductor La27(W0.85Nb0.15)5O55.5-δ are investigated by means of thermogravimetry, impedance spectroscopy, and the electromotive force (EMF) method as a function of temperature, water vapor, and oxygen partial pressures, as well as isotope exchange measurements in order to elucidate the mechanism and thermodynamics of protons formation and transport. The highest proton conductivity, 1.3 3 10-3 S/cm, is achieved at 700°C in wet O2. Proton selfdiffusion coefficients are estimated from thermogravimetric measurements of hydration and conductivity data. Comparison of the conductivity characteristics between nominally pure and Nb-substituted materials reveals that the ionic conductivity increases and the activation energy decreases with Nb doping. These differences are discussed to reflect changes in the structure promoting ionic transport rather than changing the concentration of defects to any large extent. [ABSTRACT FROM AUTHOR]

LaNb 1− x Mo x O x with x = 0, 0.10, 0.15, 0.20 and 0.30 were prepared by a step-firing procedure to avoid Mo volatilization, and investigated by X-ray diffraction, thermal expansion and electrical measurements. Doping LaNbO 4 with Mo tended to stabilize the high temperature tetragonal phase to room temperature, at which single tetragonal phase was achieved only in LaNb 0.8 Mo 0.2 O 4 . The total conductivity of LaNb 0.8 Mo 0.2 O 4 was 2.65 × 10 −2 and 8.11 × 10 −2 S cm −1 at 900 °C in air and 5 vol.% H 2 –N 2 , respectively. At temperatures between 500 and 900 °C, the ion transport number of LaNb 0.8 Mo 0.2 O 4 was above 0.95 in the oxidizing atmosphere and below 0.51 in the reducing atmosphere. The high conductivity and mixed conduction in the reducing atmosphere were related to the valence change of some Mo ions from +6 to + δ (≤4). The reduced LaNb 0.8 Mo 0.2 O 4 transformed from the tetragonal to the monoclinic structure, and the tetragonal structure was restored by subsequent oxidation in air. [ABSTRACT FROM AUTHOR]

A newly developed interconnect alloy for solid oxide fuel cells, containing Fe, Cr, Mn and Mo as well as other minor elements and designated as FeCM, is investigated on its poisoning effect on (La 0.8 Sr 0.2 ) 0.95 MnO 3−δ (LSM) cathode by electrochemical impedance spectroscopy and microstructure observation. Compared with commercial SUS430 stainless steel, which is usually used as a essential interconnect in the SOFCs stacks, the FeCM alloy as the interconnect reduces the ohmic of the cell (R Ω ) and polarization resistance of the cathode (R P ) and increases the electrochemical performance of the cathode. At 850 °C the R Ω remains almost unchanged at a level slightly above 2.0 Ω cm 2 and the R P decreases from 5.76 to 1.68 Ω cm 2 within 20 h, while the cathode potential at 200 mA min −1 is virtually stabilized at below 1.0 V and the overpotential is decreased from 0.43 to 0.16 V. Based on the evidence of a narrower oxide deposition zone on the electrolyte surface near the cathode and a deposition-free cathode/electrolyte interface, this improvement is attributed to the reduced degree of volatilization of oxide scale formed on the surface of the FeCM alloy. [ABSTRACT FROM AUTHOR]