Functional materials at the flick of a switch

The function of materials that have been coated with an ionic liquid can be altered by applying an electric field to shuttle ions in and out. The technique has been used to make materials that have switchable properties. See Letter p.124 Changing to the next phase Materials that change their phase in response to the electrical injection or extraction of an ionic species are harnessed in a wide range of applications, including batteries that can operate in a range of climates and smart windows that can control the amount of light or heat that passes through them. As Nianpeng Lu et al . report, increasing the number of transferrable ionic species can greatly enhance the functionality of the system. Specifically, they report a material system in which the electrical insertion and extraction of oxygen (O 2− ) and hydrogen (H + ) ions can be independently controlled, giving reversible access to three distinct material phases that have very different optical, electrical and magnetic properties. This finding could further broaden the range of potential applications for phase-changing materials.