Potential Gradient Electrolyte System Design for Fast and Stable Self-Switching Electrochromic Energy-Storage Device

Electrochromic (EC) smart windows are promising for both energy-savings and energy-storage in buildings. However, conventional EC devices require external power to operate. Herein, we propose a potential-gradient electrolyte composed of KCl and K2S2O8 solutions that are separated by a cation exchange membrane (CEM), which is sandwiched between Zn and Prussian blue (PB) electrodes to achieve a self-powered EC device, where large potential-differences between Zn and PB and between PB and K2S2O8 can be built. Therefore, the device can be chemically self-discharged and self-recharged by the potential-difference-driven spontaneous redox reaction between PB and Prussian white (PW), enabling fast self-bleaching/self-coloration time of 3.6/10.3 s by connecting/disconnecting the Zn and PB electrodes. Moreover, the CEM is capable of preventing the Zn electrode from being dissolved and corroded by K2S2O8 solution, endowing the device with a stable self-switching feature. Our strategy of a potential-gradient electrolyte system design paves the new way for developing stable and fast self-switching EC energy-storage devices.