Structure modulated amorphous/crystalline WO₃ nanoporous arrays with superior electrochromic energy storage performance

In this work, porous bilayer hybrid WO₃ nanoarray devices are constructed in which the active materials are composed of a crystalline WO₃ nanobowl arrays layer modified by a nanoholey amorphous WO₃ layer. The hybrid nanoarrays exhibit outstanding electrochromic performance with high color contrast in both visible and near infrared regions (93.9% at 633 nm, 89.6% at 1500 nm), fast response speed (3.0 s for coloring and 3.6 s for bleaching), exceptional cycling stability (95.4% contrast retention after 10,000 cycles) and decent coloring efficiency (92.3 cm²C^-1) at low colored/bleached potentials (-1.0/1.0 V). In addition, the hybrid nanoarrays display high areal capacitance (47.4 mF/cm²), superior rate capability and cyclic stability (areal capacitance remains 84.0% after 2000 cycles). An electrochromic supercapacitor nanodevice is constructed based on the excellent electrochromic and capacitive performance of the hybrid nanoarrays. The enhanced electrochemical properties can be ascribed to the synergistic effect between the unique top amorphous layer structure and the underlying crystalline WO₃ layer. In addition, oxygen partial pressure plays a crucial role in modulating the microstructure of the amorphous layer as well as electrochemical performance of the nanodevice. The obtained hybrid WO₃ nanoarrays as well as the structure modulation promise great potential in developing high quality smart energy-efficient devices.