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

Abstract

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.

Enhancing the Spectroelectrochemical Performance of WO3 Films by Use of Structure-Directing Agents during Film Growth

“…Less charge is needed to allow a high transmittance modulation for the films with interconnected micropores compared to the compact or just mesoporous films. Such enhancement of CE by using appropriate structure-directing agents is in good accordance with earlier reports [27,31]. The highest obtained values for ∆T 710nm and CE 710nm for the porous films were reached for WO 3| µmp, similar or even better than those measured for commWO 3 , the commercial benchmark sample, speaking in favor of the present films with a combination of mesopores interconnected by micropores.…”

“…Such surface area is compatible with the presence of micropores between grains of the films (Figure 1d). The values of S BET of the WO 3| mp films and WO 3| µmp films turned out in the same range as reported for WO 3 nanoflakes (~10 m 2 /g [55]) and mesoporous WO 3 (~32 m 2 /g [31]). S BET ∼ = 10 m 2 /g determined for the WO 3| mp films thereby confirmed the presence of mesopores within the films but the considerably higher S BET ∼ = 20 m 2 /g of the WO 3| µmp films shows the significantly increased accessibility of the mesopores by the simultaneous presence of micropores serving as interconnecting channels.…”

“…Hence, further previous studies addressed the impact of different nanoscaled porosity on the electrochromic performance. Block copolymers such as polystyrene-block-polyethylene oxide (PS-b-PEO) [31] or Pluronic P123 [32] that are forming micelles allow the formation of mesoporous films with 4-30 nm large pores providing enhanced electrochromic characteristics such as short switching time, high coloration efficiency and large transmittance modulation [31,32]. Note that in diverse previous studies films with spherical mesopores were investigated which inherently suffer from restricted connection between the spherical pores, impeding Li + diffusion [33,34].…”

Electrochromic Inorganic Nanostructures with High Chromaticity and Superior Brightness

“…Furthermore, thicker WO 3 films took longer time to switch, which is expected since Li + needs to be transported through the whole layer. The speed can likely be improved by slightly increasing the amount of nanoholes or by altering the porosity of the WO 3 , 25 but it is already sufficient for display applications where images do not necessarily need to be frequently updated (e.g., advertisement or decorative images). The coloration state is determined by the degree of Li + intercalation, which has an equilibrium state determined by the applied voltage.…”

Two-dimensional WO3 nanosheets for high-performance electrochromic supercapacitors

“…To achieve these goals, enormous efforts have been devoted to tailoring the morphology, and controlling the size and doping of the bifunctional material to enhance the electrochromic and electrochemical performances. [3][4][5][6][7][8][9][10][11] For example, Kim et al 7 reported that mesoporous amorphous WO 3 film showed higher bifunctional performance than dense WO 3 film, owing to its porous structure facilitating rapid ion transport. In addition, building a nanoarray electrode is also an effective method.…”