Synthesis of oriented core/shell hexagonal tungsten oxide/amorphous titanium dioxide nanorod arrays and its electrochromic-pseudocapacitive properties

In this work, well-aligned core/shell hexagonal tungsten oxide/amorphous titanium dioxide nanorod arrays (denoted as core/shell WTNRAs) were synthesized on FTO substrates by a hydrothermal-spin coating approach and has been proved to have enhanced electrochromic-pseudocapacitive properties compared with initial WO3 nanorod arrays (h-WNRAs). The influence of spin-coated amorphous TiO2 (a-TiO2) layer on the microstructure, electrochromic (EC) and pseudocapacitive (PC) properties of the core/shell WTNRAs was intensively investigated. With the suitable a-TiO2 shell, the core/shell WTNRAs presented good EC performance including larger optical modulation (682 nm, 78%), faster response (coloring time 15 s, bleaching time 12 s), higher coloration efficiency (800 nm, 122.3 cm(2).C-1) and good cyclic stability. In the meantime, the core/shell structures achieved excellent PC properties such as higher charge storage capacity (426.8 F.g(-1) at 1 A.g(-1)), good charge-discharge cycle efficiency (81%) and rate performance. The mechanism of improving the bifunctional properties was also discussed. Furthermore, the energy storage stages of the material could be visually monitored by rapid and reversible colour changes at different current densities.