Construction of doped-rare earth (Ce, Eu, Sm, Gd) WO3 porous nanofilm for superior electrochromic and energy storage windows

Electrochromic capacitors are attracting a huge attention due to their dual functions in energy-saving and energy storage. Electrochromic and energy storage performance of the films could be effectively improved through regulating their physical phase and morphology. In the present work, the physical phase and morphology of the WO 3 nanofilms were regulated by doping RE ions (RE = Ce, Eu, Sm, Gd) using one-step hydrothermal technology. The three-dimensional (3D) urchin-like crystal WO 3 nanofilm would transfer into the 3D nest-like WO 3 (WO 3 -RE) nanofilms that consisted of crystal and amorphous phase by doping RE ions. Compared with the pure WO 3 nanofilm, the WO 3 -RE nanofilms exhibited higher optical contrast, faster switching speed, longer cyclic stability, and larger areal capacitance owing to faster ions transfer rate and more stable film structure. The optical contrast of WO 3 -Eu and WO 3 -Sm nanofilms were 76.3% and 73.8% at 633 nm, 75.5% and 74.6% at 900 nm wavelength, respectively. Notably, the WO 3 -Eu and WO 3 -Sm nanofilms could retain 99.6% and 99.1% of their original optical contrasts after 1000 cycles, respectively. Additionally, the areal capacitance of ECDs based on the WO 3 /PB, WO 3 -Ce/PB, WO 3 -Eu/PB, WO 3 -Sm/PB, and WO 3 -Gd/PB were 26.15, 49.27, 58.23, 71.46, and 79.52 mF/cm 2 at 0.3 mA/cm 2 , respectively. ECDs based on the WO 3 -RE/PB are promising for energy-saving and energy storage dual functional smart windows.