Crystalline WO3 nanowires array sheathed with sputtered amorphous shells for enhanced electrochromic performance

Rational construction of crystalline/amorphous tungsten trioxide core/shell nanowire arrays have been obtained by combing solvothermal and magnetron sputtering techniques. High resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) characterization results reveal that the core/shell nanowires are composed of single crystal hexagonal tungsten trioxide nanocores sheathed with amorphous tungsten trioxide nanoshells. By the well-controlled sputtering technique, the thickness of the amorphous WO3 nanoshell can be precisely modulated which determines evidently electrochromic properties of the core/shell nanostructure. The optimized core/shell nanowires display exceptional electrochromic properties of high optical contrast (84.5% at 633 nm and 80.0% at 1500 nm), fast switching speeds (1.2 s for bleaching and 3.6 s for coloring), high coloration efficiency (83.6 cm(2)/C at 633 nm) and exceptional cycle stability (91.9% after 3000 cycles). The enhanced performance can be attributed to the complementary advantages of the crystalline nanocores and the well-defined amorphous nanoshells as well as their interface interaction. The strategy of synthesizing crystalline/amorphous core-shell nanoarrays proposes a reliable solution to produce high performance electrochromic materials and devices such as energy saving smart window, outdoor static displays and other energy-efficient applications.