Scientists from the U.S. Department of Energy Office of Science’s Argonne and Oak Ridge national laboratories, Northwestern University, and Hokkaido University (Japan) have developed a new oxygen “sponge” that can easily absorb or shed oxygen atoms at low temperatures. Materials with these novel characteristics would be useful in devices such as rechargeable batteries, sensors, gas converters, and fuel cells.
Materials containing atoms that can switch back and forth between multiple oxidation states are technologically important but very rare in nature. Typically, most elements have a stable oxidation state, and they want to stay there. So far there are not many known materials in which atoms are easily convertible between different valence states. This research group found a chemical substance that can reversibly change between phases at rather low temperatures without deteriorating, which is a very intriguing phenomenon.
Many energy storage and sensor devices rely on this valence-switching trick, known as a reduction-oxidation or “redox” reaction. For instance, catalytic gas converters use platinum-based metals to transform harmful emissions such as carbon monoxide into nontoxic gases by adding oxygen. Less expensive oxide-based alternatives to platinum usually require very high temperatures — at least 600 to 700 degrees Celsius — to trigger the redox reactions, making such materials impractical in conventional applications.
The team’s material consists of strontium cobaltite, which is known to occur in a preferred crystalline form called brownmillerite. Through an epitaxial stabilization process, the ORNL-led team discovered a new recipe to synthesize the material in a more desirable phase known as perovskite. The researchers have filed an invention disclosure on their findings.
The new multivalent oxygen sponges can undergo such a redox process at as low as 200º Celsius, which is comparable to the working temperature of noble metal catalysts. The material is not coming to cars tomorrow, but this discovery shows that multivalent oxides can play a pivotal role in future energy technologies.
The international team’s design and testing of this novel advanced material from scratch required multidisciplinary expertise and sophisticated tools for advanced synthesis and characterization of novel materials, including the X-ray Science Division beamline 4-ID-C of the DOE-SC’s Advanced Photon Source at Argonne and Center for Nanophase Materials Science at ORNL.
Reference: Hyoungjeen Jeen,Woo Seok Choi, Michael D. Biegalski, Chad M. Folkman, I-Cheng Tung, Dillon D. Fong, JohnW. Freeland, Dongwon Shin, Hiromichi Ohta, Matthew F. Chisholm, and Ho Nyung Lee*, “Reversible redox reactions in an epitaxially stabilized SrCoOx oxygen sponge,” Nat. Mater., advance on-line publication,( 25 August 2013). DOI:10.1038/NMAT3736