A New Family of Proton-Conducting Conducting Materials in Layered Oxides

To identify a good ionic conducting material for use as electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs) remains a big challenge. In this report, we demonstrate that good proton conductor can be obtained in transition element rich intercalation materials such as Li_xAl_0.5Co_0.5O₂. OCV of 1.0 ~ 1.1V was observed for a H₂/air fuel cell at temperature 475 – 575 °C indicating it is nearly a pure ionic conductor under fuel cell operating conditions.  A power density of 173 mW cm^-2 has been achieved at 525 °C with a thick electrolyte (0.79 mm thick) when silver was used as both cathode and anode. The ionic conductivity of LiAl_0.5Co_0.5O₂ was 0.1 S/cm at 500 °C, deduced from the series resistance of the H₂/air fuel cell. This is the highest among known poly-crystalline proton-conducting materials. This study will provide a new approach to discover new proton conducting materials for use in IT-SOFCs. It is expected that an ideal proton-conducting oxide may be identified in layered oxides.

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