A device that functions as both a self-powered electrochromic smart window and a self-recharging battery is reported in Nature Communications this week. This device may have future applications in the green building industry.

Electrochromic smart windows are designed to change their transparency when voltage is applied to them. However, conventional electrochromic smart windows and rechargeable batteries still need external power sources to operate, whereas the end goal for many green building developers is zero-energy consumption.

Xiao Wei Sun and colleagues design a new electrochromic smart window that uses aluminium and Prussian blue electrodes. The blue colour of the device can be made transparent (into Prussian white) by connecting the electrodes. Disconnecting the electrodes in the presence of an aqueous solution allows the Prussian white to revert back to Prussian blue, a reaction that stores energy like a battery. Several aspects of the devices performance will need to be improved before it will be commercially viable.