Lithium-ion batteries, fuel cells and many other devices depend on the high mobility of ions to function properly. But there are a number of obstacles to such mobility. A research team led by Jennifer LM Rupp of the Technical University of Munich (TUM) and Harry L. Tuller of the Massachusetts Institute of Technology (MIT) has just shown for the first time that light can be used to increase the mobility of ions and improve the performance of such devices.
A charge can be carried by a material in different ways. The best known is the electrical conductivity of metals, where charge is carried by electrons. In many devices, however, ions carry the charge. An example is lithium-ion batteries in which lithium ions move during charging and discharging. Similarly, fuel cells rely on the transport of hydrogen and oxygen ions to conduct electricity.
Ceramics are currently studied as solid electrolytes for the transport of oxygen ions. But: “What we find is that ionic conductivity – the speed at which ions can move and, therefore, the efficiency of the resulting device – is often markedly degraded by the fact that the ions are stuck at grain boundaries,” says Professor Harry L. Tuller of the Massachusetts Institute of Technology.
Light sets ions in motion
In their current publication, Tuller and his colleague Jennifer LM Rupp, professor of solid-state electrolyte chemistry at the Technical University of Munich, show how light can be used to reduce the barriers encountered by ions at grain boundaries. ceramics.
Many devices based on ionic conductivity, such as solid oxide fuel cells, must operate at very high temperatures for ions to cross intergranular barriers. Operating temperatures of up to 700° Celsius, however, present their own challenges: materials age faster and the infrastructure needed to maintain these high temperatures is costly.
“Our dream was to see if we could overcome the barriers by using something that doesn’t require heat. Could we get the same conductivities with another tool? says lead author and PhD student Thomas Defferriere. This tool turned out to be lightweight, which had never been studied in this context before.
Higher levels of efficiency in energy conversion and storage
“Our research shows that illuminating ceramic materials for fuel cells and possibly batteries in the future can dramatically increase ion mobility,” Rupp says. “In gadolinium-doped cerium oxide, a ceramic used as a solid-state electrolyte in fuel cells, illumination increased grain boundary conductivity by a factor of 3.5.”
This recently discovered “opto-ionic effect” could find a wide range of applications in the future. For example, it could improve the performance of solid-state electrolytes in tomorrow’s lithium-ion batteries and thereby facilitate higher charging speeds, or could pave the way for the development of new electrochemical storage and conversion technologies that operate at lower temperatures and achieve higher efficiency. levels.
Light can also be precisely focused, making it possible to spatially control the flow of ions at exactly defined points or to switch conductivity in ceramic materials.
The research was supported by the US Department of Energy under the Basic Energy Services program, the US National Science Foundation, the Japan Society for the Promotion of Science under the Core-to-Core program, the Swiss National Science Foundation, two Kakenhi Grants-In-Aid for young scientists and Equinor ASA.
Some of the research was conducted at the Materials Research Science and Technology Center at the Massachusetts Institute of Technology, and some at the Center for Nanoscale Systems, which is part of the National Science Foundation’s National Nanotechnology Coordinated Infrastructure Network.
Professor Harry L. Tuller conducts research at MIT’s Materials Research Laboratory and the International Institute for Carbon Neutral Energy Research (I2CNER) at Kyushu University. Jennifer LM Rupp is Associate Professor of Materials Science and Engineering at MIT and Professor of Solid State Electrolyte Chemistry at TUM as well as Technical Director of TUMint.Energy Research GmbH.
The title of the article
Photo-enhanced ionic conductivity across grain boundaries in polycrystalline ceramics
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Conflict of Interest Statement
The authors declare no conflict of interest.
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