Extremely fast electrochromic supercapacitors based on mesoporous WO₃ prepared by an evaporation-induced self-assembly

Mesoporous metal oxides consisting of fully interconnected network structures with small pores (20–50 nm) have high surface areas and decreased ion intercalation distances, making them ideal for use in high-performance electrochromic supercapacitors (ECSs). Evaporation-induced self-assembly (EISA), which combines sol-gel chemistry and molecular self-assembly, is a powerful method for the fabrication of mesoporous metal oxides through a solution phase synthesis. Herein, we introduce ultrafast sub-1 s ECSs based on an amorphous mesoporous tungsten trioxide (WO₃) that is prepared by EISA. Compared to that of a compact-WO₃ film-based device, the performances of an ECS with mesoporous WO₃ exhibits a large optical modulation (76% at 700 nm), ultrafast switching speeds (0.8 s for coloration and 0.4 s for bleaching), and a high areal capacitance (2.57 mF/cm²), even at a high current density (1.0 mA/cm²). In addition, the excellent device stability during the coloration/bleaching and charging/discharging cycles is observed under fast response conditions. Moreover, we fabricated a patterned mesoporous WO₃ for ECS displays (ECSDs) via printing-assisted EISA (PEISA). The resulting ECSDs can be used as portable energy-storage devices, and their electrochromic reflective displays change color according to their stored energy level. The ECSDs in this work have enormous potential for use in next-generation smart windows for buildings and as portable energy storage displays.