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3 Materials Science Poland

3 2006

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Oxide-ion conductors for fuel cells

100%

Krok F. , Abrahams I. , Wrobel W. , Kozanecka-Szmigiel A. , Dygas J. R.

Materials Science Poland

2006

tom Vol. 24, No. 1

13--22

The principal materials used in the construction of solid oxide fuel cells (SOFCs) are discussed. Some of the problems encountered with high temperature fuel cells (HT-SOFCs) might be overcome by lowering the operating temperature to 500-700 °C, through the development of suitable materials for intermediate temperature fuel cells IT-SOFCs. Candidate electrolyte materials are discussed, including cerium gallium oxide, lanthanum strontium gallium magnesium oxide, and electrolytes based on doped bismuth oxide. While high ionic conductivities can readily be achieved in these materials at intermediate temperatures, stability in reducing atmosphere is still a problem. This might be overcome by careful chemical design of electrolytes containing stabilising dopants. Two zirconia-doped bismuthate systems are discussed in this respect. In both cases, the obtained materials exhibit different structures - one is Bi3Nb1-xZrxO7-x/2 of the ?-Bi2O3 type, and the other, Bi4V2-2xZrxO11-x, has a layered structure of the Aurivillius type.

Structure and electrical properties of oxide-ion conductors in the Bi3NbO7-Bi3YO6 system

86%

Kozanecka-Szmigiel A. , Krok F. , Abrahams I. , Wrobel W. , Chan S. C. M. , Dygas J. R.

Materials Science Poland

2006

tom Vol. 24, No. 1

31--37

A study of the structure and electrical conductivity of Bi3Nb1-xYxO7-x is presented. X-ray diffraction confirms full solid solution formation in this system, with the adoption of a fluorite-type structure. Superlattice ordering of the anion sublattice is evident in neutron diffraction data, the nature of which varies with composition. At low values of x, long-range ordering is present, whereas above x = 0.4 only local ordering is observed. Arrhenius plots of the total electrical conductivity of all samples containing yttrium show two linear regions with different activation energies, with evidence for a phase transition between 450 and 680 °C.

Bi8V2O17 - a stable phase in the Bi2O3-V2O5 system

86%

Wrobel W. , Krok F. , Abrahams I. , Kozanecka-Szmigiel A. , Malys M. , Chan S. C. M. , Dygas J. R.

Materials Science Poland

2006

tom Vol. 24, No. 1

23--30

Bi8V2O17 is commonly observed as an intermediate phase in the synthesis of compounds in ternary systems of the type Bi2O3-V2O5-MexOy. It is also seen as an end product at particular compositions in these systems. A rhombohedral substructure model for this phase is presented along with electrical parameters. Evidence from the Arrhenius plot suggests a phase transition at around 550 °C. The existence of a limited solid solution of Bi8V2O17 with ZrO2 is also discussed.