Proton and Redox Couple Synergized Strategy for Aqueous Low Voltage-Driven WO₃ Electrochromic Devices

Aqueous electrolytes possess non-combustible and eco-friendly features compared to organic electrolytes, leading them to be more suitable for application in smart windows for daily use. However, limited by the narrow electrochemical window of water (1.23 V), its use in conventional electrochromic devices (ECDs) would result in irreversible performance loss, which arises from decomposition caused by high voltage. Here, we propose a synergistic scheme combining a redox couple-catalytic counter electrode (RC-CCE) strategy with protons as guest ions. With the help of the intelligent matching of the reaction potentials of the RC and amorphous WO₃ electrochromic electrodes and the highly active and fast kinetic features of protons, it successfully reduces the working voltage range of the device to 1.1 V. The assembled HClO₄-ECD can possess an overall modulation rate (350-1200 nm) of 0.43 and 0.94 at -0.1 and -0.7 V, respectively, and a modulation of 66.8% at 600 nm at -0.7 V. Moreover, compared with other guest ions, the proton-based ECD exhibits higher coloration efficiency, a broader color modulation capability, and better stability. In addition, the house model equipped with the proton-based ECD effectively blocks solar radiation, which provides a potential solution for the design of aqueous smart windows.