Structure engineering in hexagonal tungsten trioxide/oriented titanium dioxide nanorods arrays with high performances for multi-color electrochromic energy storage device applications

• A novel porous structure of WO 3 /TiO 2 was fabricated by a hydrothermal method. • Superior transmittance modulation and fast Li + ions insertion kinetics was obtained. • V 2 O 5 is chosen as counter electrode based on the strategy of color superposition. • EESD can supply six multi-color modulation modes and light up a LED. A novel porous structure of hexagonal WO 3 /oriented TiO 2 nanorods arrays ( h -WO 3 /TiO 2 NRAs) hybrid film was successfully prepared by a facile hydrothermal method. Benefiting from elaborately structure engineering, the hybrid film exhibited large transmittance modulation (ΔT 633nm = 73.45%), high coloration efficiency (69.2 cm 2 ·C -1 ), fast Li + ions insertion kinetics (6.6 s/2.0 s for t c / t b ), stable cyclic stability (maintains 92.9% of initial ΔT after 2000 cycles) as well as areal specific capacitance of 10.93 mF·cm −2 at the current density of 0.1 mA·cm −2 . An electrochromic energy storage device (EESD) with six multi-color modulation modes (light gray, dark olive green, yellow green, lime green, dark green and dark blue) was successfully assembled by h -WO 3 /TiO 2 NRAs hybrid film and electrodeposited-V 2 O 5 film. Based on the excellent electrochromic and pseudocapacitive properties, the EESD promised a smart visual monitoring of the energy storage level and can light up a LED after charging, indicating a good energy storage application prospect.