Professor SHIMAKAWA, Yuichi and his research group “Oxygen diffusion at low temperature in perovskite-structure iron oxides” (Published in “Nature Chemistry” Advanced Online Publications, February 8, 2010)

Professor SHIMAKAWA, Yuichi and his research group

(Laboratory of Advanced Inorganic Synthesis,
Division of Synthetic Chemistry)

 

“Oxygen diffusion at low
temperature in perovskite-
structure iron oxides”

 

A new insight into development of
solid-oxide fuel cells operating at low temperature

Drs. Kawai M, Prof. Shimakawa Y, Mr Inoue S,
and Ichikawa M (from left)

Mr. S. Inoue (alumnus), Drs. M. Kawai (Doctor course student), N. Ichikawa (Assist. Prof.), and Y. Shimakawa (Prof.) in Advanced Solid State Chemistry Laboratory revealed anisotropic oxygen diffusion at low temperature in perovskite-structure iron oxides.  The result gives a new insight into developing future electrolytes in solid-oxide fuel cells operating at low temperature.

Oxygen-ion conduction in transition-metal oxides is exploited in, for example, electrolytes in solid-oxide fuel cells and oxygen-separation membranes, which currently work at high temperatures. Conduction at low temperature is a key to developing further utilization, and an understanding of the structures that enable conduction is also important to gain insight into oxygen-diffusion pathways. We report the structural changes observed when single-crystalline, epitaxial CaFeO2.5 thin films were changed into CaFeO2 by low-temperature reductions with CaH2.
During the reduction process from the brownmillerite CaFeO2.5 into the infinite-layer structure of CaFeO2, some of the oxygen atoms are released from and others are rearranged within the perovskite-structure framework. We evaluated these changes and the reaction time they required, and found two oxygen diffusion pathways and the related kinetics at low temperature. The results demonstrate that oxygen diffusion in the brownmillerite is highly anisotropic, significantly higher along the lateral direction of the tetrahedral and octahedral layers.
The present findings have great impacts on not only research fields of fundamental solid state chemistry but also technological application fields of fuel cells.

The research was done in collaboration with H. Kageyama (Prof.) in Graduate School of Engineering, Kyoto University, and W. Paulus (Prof.) in University Rennes 1, France.  The results were published in Nature Chemistry (Advanced Online Publications, February 8, 2010)