Multivalent oxygen sponge that works at 200°C
A team of scientists have managed to create an oxygen ‘sponge’ that can absorb and shed oxygen atoms at temperatures as low as 200°C. The process was developed by a research team from U.S. Department of Energy’s Oak Ridge National Laboratory (ORNL).
‘Typically, most elements have a stable oxidation state, and they want to stay there,’ said ORNL’s Ho Nyung Lee, who led the project. ‘So far there aren’t many known materials in which atoms are easily convertible between different valence states. We’ve found a chemical substance that can reversibly change between phases at rather low temperatures without deteriorating, which is a very intriguing phenomenon.’
Valence switching is often referred to as a reduction-oxidation (redox) reaction. The characteristic of altering oxidation states is useful in a wide range of devices, including rechargeable batteries, sensors and gas converters. Platinum-based metals are commonly used in catalytic converters. There are cheaper valence switching alternatives but these come with a different price. Typically they require temperatures of at least 600°C to spark a redox reaction. Obviously this rules them out of many potential applications.
‘We show that our multivalent oxygen sponges can undergo such a redox process at as low as 200°C, which is comparable to the working temperature of noble metal catalysts,’ Lee said. ‘Granted, our material is not coming to your car tomorrow, but this discovery shows that multivalent oxides can play a pivotal role in future energy technologies.’
The material consists of strontium cobaltite. The common crystalline form of this is brownmillerite – but through an epitaxial stabilization process the team discovered how to synthesise the material to perovskite form.
‘These two phases have very distinct physical properties. One is a metal, the other is an insulator. One responds to magnetic fields, the other does not and – we can make it switch back and forth within a second at significantly reduced temperatures,’ Lee added.
Image credit: U.S. Department of Energy, Oak Ridge National Laboratory