Insights into nucleation, growth and phase selection of WO3: morphology control and electrochromic properties

Abstract

Electrochromic application of nanoscale WO₃ demands stringent control in terms of phase-purity and morphology. Here, we show that two different phases of WO₃ with distinct morphologies (viz. 2D plates of orthorhombic phase and 1D rods of hexagonal phase) can be obtained by tuning the solvothermal reaction conditions. Control experiments along with density functional theory based ab initio calculations show that the reaction pathway critically depends on the capping agent used in the reaction. Using this concept in conjunction with crystallographic arguments, we rationalize the morphology evolution of the two phases. Furthermore, the synthesized phases exhibit very different electrochromic properties in terms of H⁺ diffusion, which can be rationalized by the calculated trend in the H⁺-intercalation energies.