The Department of Energy, Office of Science has announced the Pacific Northwest National Laboratory (PNNL) discovered a new metal oxide that allows oxygen ions to move through the material quickly and easily at lower temperatures.

The new metal oxide’s atomic structure includes highly ordered arrays of missing oxygen atoms. This structure allows oxygen ions to move through the material quickly and easily at lower temperatures, close to ~250º C (480º F).

Materials that allow easy movement of oxygen ions are essential for solid oxide fuel cells. The material discovered in this research could enable more efficient solid oxide fuel cells to operate at much lower temperatures than current technology running at ~800°C (1470º F).

The group’s study paper has been published in Nature Communications.

Metal oxides are important materials found in many energy technologies such as fuel cells, superconductors, and thermoelectric systems. Most metal oxides contain oxygen deficiencies or vacancies as point defects which are often uniformly distributed in the material.

Improved Metal Oxide for Fuel Cells. Click image for more info.

Improved Metal Oxide for Fuel Cells. Click image for more info.

A challenging goal is controlled generation and positioning of these oxygen deficiencies to create novel structures and functional properties. PNNL researchers have accomplished just that in their discovery of a new, non-stoichiometric metal oxide SrCrO2.8. While attempting to prepare thin films of stoichiometric SrCrO3.0, they found that a non-stoichiometric form with the composition SrCrO2.8 is formed instead.

This new material contains ordered arrays of SrO2 planes interleaved between layers of tetrahedrally coordinated Cr+4 ions and separated by ~1nm. Moreover, when mildly heated in air, it reversibly transforms from a semiconducting form with rhombohedral (diamond-like) structure to a metallic form with a so-called cubic perovskite structure. The ordered oxygen vacancies in the rhombohedral form allow oxygen ions to diffuse through the material quickly and easily at the lower temperatures.

This property is exceedingly important for solid oxide fuel cell technology which currently requires very high operating temperatures. First-principle calculations provided insights into the formation and stability of the non-stoichiometric SrCrO2.8 and how oxygen ions could move so easily through the material. The aggregation of oxygen vacancy defects into ordered arrays is a property of interest for not only more efficient solid oxide fuel cells but also would be useful for other applications such as thermoelectrics.

Operating temperatures of 800º C (1470º F) coming down to 250º C (480º F) is no small thing and should help a great deal in getting economically viable fuel cells closer to mass market. All the other components in a fuel cells may well be less expensive and last much longer. Hopefully this is a breakthrough that makes a big difference.


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