Artistic illustration of the bi-functional device of self-powered electrochromic window and self-rechargeable transparent battery. (Credit: Xiao Wei Sun)
Smart windows that change color to provide more shade when an electrical current is applied could keep buildings cool and reduce the energy burden of using air conditioning. However, the fact that they need electricity to operate diminishes their efficiency. But now scientists have developed a smart window that can also serve as a battery: It recharges upon with oxygen, allowing it to power its own electrochromic activity.
The device consists of glass coated with a transparent electrically conductive material and a film of . When this film is connected to both an aluminum electrode and a liquid electrolyte, an electric current flows and turns the Prussian blue into a transparent mineral known as Prussian white. When disconnected, the Prussian white chemically reacts with nearby oxygen and reverts to Prussian blue.
The Prussian blue film and the aluminum electrode can also serve as a battery's positively and negatively charged terminals, respectively, and can even power a device they are hooked up to. When this battery runs out of juice, the Prussian blue turns into colorless Prussian white. Once again, when the Prussian white is exposed to oxygen, it transforms back into Prussian blue and the battery gets recharged.
In theory, the smart window can work without consuming any extra electricity, though in practice it may need an outside power source depending on how frequently it switches its transparency on and off. Future research needs to explore how reliable the device is and how long it can last, says study co-author , an electronic engineer at Nanyang Technological University in Singapore. Sun and his colleagues detailed in the journal Nature Communications.