Solid-state electrolytes have been the focus of much research in the fields of lithium-ion (Li-ion) batteries and hydrogen fuel cells because they are safer and less toxic than liquid electrolytes. But there’s a hold-up, literally. Ionic conductivity – the rate at which ions move and, therefore, how efficient a device can be – is hampered by the fact they get blocked at granular boundaries in the material.
In the case of solid-oxide fuel cells, operating them at high temperatures (up to 700°C) helps the ions to transverse the boundaries, but heating is expensive and unsustainable, as it degrades the material. To solve this problem, an international team from the Technical University of Munich (TUM) and the Massachusetts Institute of Technology (MIT) in the US have been experimenting with using light to assist ion transport – and the results are promising.
“Our research shows that illumination of ceramic materials for fuel cells and possibly for batteries in the future can significantly increase ion mobility,” says Jennifer Rupp, professor for solid-state electrolyte chemistry at the TUM in a . “In gadolinium-doped cerium oxide, a ceramic used as a solid-state electrolyte in fuel cells, illumination increased conductivity at the grain boundaries by a factor of 3.5.”
When light is used as an accelerator, it can be focused precisely to control the flow of ions at specific points, or to improve conductivity in ceramic materials, offering a clear advantage over thermal techniques. This newly discovered “opto-ionic” effect could be used in a number of applications from solid-state Li-ion to electrochemical storage and conversion technologies to achieve higher efficiency rates at lower temperatures.