Tungsten oxide (WO_3) thin film mesophases encompassing a well-organized network of grains with a triclinic phase and pores with diameters in the range of 2-5 nm were generated at room temperature by template-assisted electrodeposition involving a novel combi-nation of ionic and polymeric surfactants. Electron microscopy studies revealed the surface texture of the films annealed at 250 and 500 deg C to be primarily composed of randomly oriented rod and sheet-like shapes and the bulk structure of these films to ensconce fibril-like shapes and distinct spherical nanoparticles, along with elongated pores. Coloration efficiency, transmission modulation and charge density for lithium insertion are greater, switching rates are faster (colors in 8.8 s and bleaches in 1.5 s for a 50 percent transmittance change) and cycling stability is superior for the as-deposited film as compared with the annealed WO_3 films. The superior electrochromic performance characteristics of the as-deposited WO_3 coatings are a direct manifestation of the mesoporosity over multiple length scales, a good lateral organization of grains and pores which facilitate ion insertion and extraction, and a large number of accessible surface sites which ensure a high proportion of W~(5+) color centers in the film upon lithium intercalation. In spite of the retention of a porous structure by the film annealed at 500 deg C, the poor electrochromic response of the annealed films is attributed to the coarse grain rod-, sheet- and liber-like framework, which efficiently obstructs lithium ion movement and uptake.
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