Researchers from Japan's Tsukuba University have found that ultraviolet light can modulate oxide ion transport in a perovskite crystal at room temperature.
The performance of battery and fuel cell electrolytes depends on the motions of electrons and ions within the electrolyte. Modulating the motion of oxide ions within the electrolyte could enhance future battery and fuel cell functionality by increasing the efficiency of the energy storage and output. Use of light to modulate the motions of ions - which expands the source of possible energy inputs - has only been demonstrated thus far for small ions such as protons. Overcoming this limitation of attainable ion motions is something the researchers in this study aimed to address.
"Traditionally, transport of heavy atoms and ions in solid-state materials has been challenging," says co-senior author of the study Professor Masaki Hada. "We set out to devise an easy means to do so in a way that seamlessly integrates with sustainable energy inputs."
To do this, the researchers focused on cobalt double-perovskite crystals that are similar to common materials in fuel cell research. They found that shining ultraviolet light on the crystals at room temperature displaces oxide ions without destroying the crystals, meaning that the function of the crystals was retained.
"Electron diffraction results, spectroscopy results, and corresponding calculations confirmed this interpretation," explains Professor Hada. "At a delivered energy of 2 millijoules per square centimeter, approximately 6% of the oxide ions undergo substantial disorder in the crystals within several picoseconds, without damaging the crystal."
Cobalt-oxygen bonds ordinarily dramatically restrict oxide motion, but ultraviolet-light-induced electron transfer can break these bonds. This facilitates oxide ion motion in a way that accesses several states that are pertinent to storing the light energy input.
These results could have diverse applications. A greater understanding of how to use light to manipulate crystal structures that are pertinent to energy storage, in a way that does not damage the crystals, will bring about new possibilities in commercial-scale renewable energy systems.